Monday, August 16, 2010

Molluscs - Phylum Mollusca

Molluscs - Phylum Mollusca

Molluscs (Phylum Mollusca) are invertebrates that include animals such as squid, octopuses, cuttlefish, nudibranchs, snails, slugs, limpets, sea hares, mussels, clams, oysters, scallops, as well as many lesser known creatures. There are an estimated 100,000 species of molluscs making them second largest phylum in the animal kingdom, having fewer species than only the Phylum Arthropoda.
Molluscs have soft bodies that consist of three basic parts, a foot, a visceral mass, and a mantle. Because molluscs are very diverse and come in many different shapes and sizes it is difficult to make too many generalizations about the group's anatomical structure beyond these three basic parts.
The foot functions in locomotion and in molluscs that posses a shell, the foot can often be drawn inside. The visceral mass, located above the foot, contains the digestive system, the heart, and other internal organs. Finally, the mantle is a layer of tissue that covers the visceral mass and in many molluscs it contains glands which secrete a hard shell.
The majority of marine molluscs begin their life as ciliated, free-swimming larvae that later develop into adult form. Freshwater and terrestrial snails develop within the egg and emerge as tiny but fully-formed versions of the adult form. Molluscs are most diverse in marine habitats but also inhabit freshwater and terrestrial habitats.

Classification:

  • Kingdom: Animalia
  • Phylum: Mollusca
    The Phylum Mollusca contains the following subgroups:
    • Class: Aplacophora (solenogasters, deep-sea wormlike creatures)
    • Class: Bivalvia (clams, oysters, scallops, mussels)
    • Class: Cephalopoda (squid, octopodes, nautilus, cuttlefish)
    • Class: Gastropoda (nudibranchs, snails, slugs, limpets, sea hares, and relatives)
    • Class: Monoplacophora (deep-sea limpet-like creatures)
    • Class: Polyplacophora (chitons)
    • Class: Scaphopoda (tusk shells)

 

Gastropods (Class Gastropoda) include a wide variety of organisms such as terrestrial snails and slugs, sea slugs, sea hares, sea butterflies, canoe shells, conchs, whelks, limpets, periwinkles, oyster borers, coweries, nudibranchs, and many others. The Gastropoda group is the largest of all mollusc groups, with approximately 40,000 living species and fossil evidence of over 15,000 extinct species.
The unifying characteristics of gastropods include:
  • most have a single spirally coiled shell
  • undergo torsion during development
  • posess a mantle cavity and mantle
  • posess a muscular foot
  • most are dioecious but some (such as snails) are hermaphroditic

Classification:

  • Kingdom: Animalia
  • Phylum: Mollusca
  • Class: Gastropoda
    The Class Gastropoda contains the following subgroups:
    • Subclass: Opisthobranchia (opisthobranchs)
    • Subclass: Prosobranchia

 Structure of a Snail Shell

Helix Garden Snail (Helix pomatia)
Photo © Elisa Locci / Shutterstock.

Shell Structure

A snail's shell is secreted by glands in its mantle rim and consists of three layers:
  • hypostracum - the innermost layer, closest to the snail's body
  • ostracum - middle, shell building layer, consists of prism-shaped calcium carbonate crystals and organic (proteid) molecules
  • periostracum - outermost layer, consists of conchin (a mixture of organic compounds), gives the shell color

Shell Function

The snail's shell serves to protect its internal organs, prevent water loss, provide shelter from cold, and protect the snail from predators.


Snail Classification

A Natural History of Terrestrial Snails

Photo © Milos Luzanin / Shutterstock.

About Snails

Snails are invertebrates, which means they lack a backbone. They belong to a large and highly diverse group of invertebrates known as the Phylum Mollusca (also known more commonly as 'mollusks'). The Phylum Mollusca includes slugs, clams, oysters, mussels, squids, octopuses, and nautiluses, in addition to snails.

Scientific Classification

In scientific terms, snails are classified into the following hierarchy of animal groups:

What Classification Reveals About Terrestrial Snails

Each of these levels of classification tells us a bit about snails in increasingly specific terms. For example, because snails are animals, they possess the characteristics shared by most animals: they are multicellular and are heterotrophs.
Since terrestrial snails are classified as mollusks and gastropods, they posses the typical characteristics of those groups too. They have a single, often spirally coiled shell (univalve), they undergo a developmental process called torsion, and they possess a mantle and a muscular foot used for locomotion.
Finally, because terrestrial snails are grouped with terrestrial slugs into the Order Stylommatophora, they share some similarities with terrestrial slugs. Because sea slugs and sea hares are in a different order, terrestrial snails have less in common with sea slugs and sea hares than they do with terrestrial slugs. Members of the Order Stylommatophora are characterized by having eyes on the top of tentacles (sea snails have eyes at the base of their tentacles).

Pulmonates

Terrestrial snails belong to a group within the Order Stylommatophora called the 'pulmonates'. This classification level is as yet unassigned (it is not officially a family) but the term pulmonate is used to refer to air-breathing land snails.

Snail Diet and Feeding Habits

A Natural History of Terrestrial Snails

Photo © Sándor Kárpisz / Shutterstock.

Diet

Terrestrial snails are herbivorous. They feed on plant material (such as leaves, stems, and soft bark), fruits, and algae.

Mouthparts

Snails have a rough tongue called a radula that they use to scrape bits of food into their mouths. They also have rows of tiny teeth made of chiton.

Calcium

Snails need calcium to build their shells. Snails obtain calcium from a variety of sources such as dirt and rocks (they use their radula to grind bits from soft stones such as limestone). The calcium snails ingest is absorbed during digestion and is used by the mantle to create the shell.

Snail Habitat / Adaptation

A Natural History of Terrestrial Snails

Photo © Marcos Teixeira de Freitas / Shutterstock.

Habitat

Snails first evolved in marine habitats and later expanded into freshwater and terrestrial habitats. Terrestrial snails live in moist, shady environments such as forests and gardens.

Adaptation

A snail's shell provides it with protection from changing weather conditions. In arid regions, snails have thicker shells that help them retain their body moisture. In humid regions, snails tend to have thinner shells. Some species burrow into the ground where they remain dormant, waiting for rain to soften the ground. In cold weather, snails hibernate.

How Snails Move

Natural History of Terrestrial Snails

Photo © Lee Ruff / Shutterstock.

How Snails Get Around

Terrestrial snails move using their muscular foot. By creating an undulating wave-like motion along the length of the foot, a snail is able to push against a surface and propel its body forward, albeit slowly. At top speed snails cover a mere 3 inches per minute. Their progress is slowed by the weight of their shell. In proportion to their body size, the shell is quite a load to carry.

A Trail of Slime

To help them move, snails secrete a stream of slime (mucus) from a gland located at the front of their foot. This slime enables them to glide smoothly over many different types of surface and helps to form a suction that helps them cling to vegetation and even hang upside down.

Refs:

For a list of sources used in the creation of this visual guide, please see the Recommended Reading page.

Snail Life Cycle / Development

A Natural History of Terrestrial Snails

Photo © Milos Luzanin / Shutterstock.

From Egg to Adult

Snails start life as an egg buried in a nest a few centimeters below the surface of the ground. Snail eggs hatch after about two to four weeks depending on the weather and environmental conditions (most importantly, temperature and soil moisture). After hatching, the newborn snail sets out on an urgent search for food.
The young snails are so hungry, they feed on the leftover shell and any nearby eggs that have not yet hatched. As the snail grows, so does its shell. The oldest part of the shell is located at the center of the coil while the most recently added parts of the shell are at the rim. When the snail matures after a few years, the snail mates and lays eggs, thus completing the full life cycle of a snail.

Snail Senses

A Natural History of Terrestrial Snails

Photo © Milos Luzanin / Shutterstock.

Sight

Terrestrial snails have primitive eyes (referred to as 'eyespots') that are located on the tips of their upper, longer pair of tentacles. But snails don't see in the same way we do. Their eyes are less complex and provide them with a general sense of light and dark in their surroundings.

Touch

The short tentacles located on a snail's head are very sensitive to touch sensations and are used to help the snail build a picture of its environment based on feeling nearby objects.

Hearing

Snails don't have ears but instead use their bottom set of tentacles to pick up sound vibrations in the air.


Evolution of Snails

Natural History of Terrestrial Snails

Photo © Dragos Constantinescu / Shutterstock.

Early Snails

The earliest known snails were similar in structure to limpets. These creatures lived in shallow sea water and fed on algae and they had a pair of gills. The most primitive of the air-breathing snails (also called pulmonates) belonged to the Family Ellobiidae. Members of this family still lived in water (salt marshes and coastal waters) but they went to the surface for air. Today's land snails evolved not from this group but from the Family Endodontidae, a group of snails that had similar characteristics to the Family Ellobiidae.

Tendencies in Snail Evolution

When we look back through the fossil record, we can see various tendencies in how snails changed over time. In general the following patterns emerge:
  • the process of torsion becomes more prominant
  • the shell became increasingly conical and spirally coiled
  • there is an evolutionary tendency among pulmonates towards the entire loss of a shell
Snail Estivation and Hibernation

A Natural History of Terrestrial Snails

Photo © Alexey Biryukov / Shutterstock.

Estivation

Snails are usually active in the summer, but if it gets too warm or too dry for them, they enter a period of inactivity known as estivation. They find a safe place—such as a tree trunk, the underside of a leaf, or a stone wall—and suction themselves onto the surface as they retreat into their shell. Thus protected, they wait until the weather becomes more suitable. Occasionally, snails will go into estivation on the ground. There, they go into their shell and a mucous membrane dries over the opening of their shell, leaving just enough space for air to get inside allowing the snail to breath.

Hibernation

In late fall when temperatures drop, snails go into hibernation. They dig a small hole in the ground or find a warm patch, buried in a pile of leaf litter. It is important that a snail finds a suitably protected place to sleep to ensure its survival through the long cold months of winter. They retreat into their shell and seal its opening with a thin layer of white chalk. During hibernation, the snail lives on the fat reserves in its body, built up from a summer of eating vegetation. When spring comes (and with it rain and warmth), the snail wakes and pushes the chalk seal to open the shell once again. If you look closely in spring, you may find a chalky white disc on the forest floor, left behind by a snail that has recently come out of hibernation.

How Large Do Snails Grow?

Natural History of Terrestrial Snails

Photo © Fernando Rodrigues / Shutterstock.

Snail Size

Snails grow to a variety of different sizes depending on the species and individual. The largest known land snail is the Giant African Snail (Achatina achatina). The Giant African Snail has been known to grow to lengths of up to 30cm.

Snail Anatomy

A Natural History of Terrestrial Snails

Photo © Anette Linnea Rasmussen / Shutterstock.

Parts of the Body

Snails are very different from humans so when we think about body parts, we're often at a loss when relating the familiar parts of a human body to snails. The basic structure of a snail consists of the following body parts:
  • foot
  • head
  • shell
  • visceral mass
The foot and head are the parts of the snail's body that we can see outside its shell, while the visceral mass is located within the snail's shell and includes the snail's internal organs.

Internal Organs

A snail's internal organs include:
  • a lung
  • digestive organs (crop, stomach, intestine, anus)
  • a kidney
  • a liver
  • reproductive organs (genital pore, penis, vagina, oviduct, vas deferens)

Nervous System

A snail's nervous system is made up of numerous nerve centers that each control or interpret sensations for specific parts of the body:
  • cerebral ganglia (senses)
  • buccal ganglia (mouthparts)
  • pedal ganglia (foot)
  • pleural ganglia (mantle)
  • intestinal ganglia (organs)
  • visceral ganglia
Reproduction in Snails

A Natural History of Terrestrial Snails

Photo © Hannu Liivaar / Shutterstock.

Reproduction

Most terrestrial snails are hermaphroditic which means that each individual possesses both male and female reproductive organs. Although the age at which snails reach sexual maturity varies among species, it may be up to three years before snails are old enough to reproduce. Mature snails begin courtship in early summer and after mating both indivudals lay fertilized eggs in nests dug out of moist soil. It lays several dozen eggs and then covers them with soil where the stay until they are ready to hatch.
Vulnerability of Snails

A Natural History of Terrestrial Snails

Photo © Jean Schweitzer / Shutterstock.

Living in a Dangerous World

Snails are small and slow. They have few defenses. They must retain enough moisture so their tiny bodies don't dry out, and they must obtain enough food to give them energy to sleep through the long cold winter. So despite living in tough shells, snails are, in many ways, quite vulnerable.

Smart Ways Snails Protect Themselves

The good news is that snails are quite clever and are well adapted to deal with the threats they face. Their shell provides them with good, impenetrable protection from weather variations and some predators. During the daylight hours, they usually hide. This keeps them out of the way of hungry birds and mammals and also helps them conserve moisture.

Battling Humans

Snails aren't too popular with some humans. These little creatures can to quickly eat their way through a carefully tended garden, leaving a gardener's treasured plants all but bare. So some people leave poisons and other snail-deterents around their yard, making it very hazardous for snails. Also, since snails don't move quickly, they are frequently in danger of crossing paths with cars or pedestrians. So be careful where you step if your walking on a moist evening when snails are out and about

Snail Strength

A Natural History of Terrestrial Snails

Photo © Maxim Amelin / Shutterstock.

Slow but Strong

Snails can haul up to 10 times their own weight when crawling up a vertical surface. When gliding along horizontally, they can carry up to 50 times their weight.

Longevity of Snails

A Natural History of Terrestrial Snails

Photo © Milos Luzanin / Shutterstock.

How Long Do Snails Live?

Snails live on average 5 to 10 years, though some have been known to live up to 15 years.

Predators

A Visual Guide to Terrestrial Snails

Photo © Teo / Shutterstock.

Predators

Snails must try their best to steer clear of a wide variety of predators. Animals that feed on snails include birds (such as blackbirds and song thrushes) and mammals (including rats, mice, moles, rabbits, hedgehogs, foxes, and humans).

Malacology

A Visual Guide to Terrestrial Snails

Photo © Jean Schweitzer / Shutterstock.

What is Malacology?

Malacology is the study of mollusks. A malacologist is a scientist whose research focuses on mollusks (and this includes the study of snails).

Glossary of Snail Terms

Natural History of Terrestrial Snails

Photo © Ajt / Shutterstock.

Glossary

The following list of words highlights the terms used in this visual guide used to describe different aspects of snails:
Recommended Reading

A Visual Guide to Terrestrial Snails

Photo © Erik Reis / Shutterstock.

Recommended Reading

If you would like to learn more about snails, I'd highly recommend the book Life of the Snail by Theres Buholzer. Though written for a young adult audience, it is packed with facts that are suited for youngsters and adults alike. The book follows the lives of a group of snails throughout an entire year and integrates a wide range of facts with an approachable writing style.
If you're looking for a resource on the Web that's packed with information about snails, I highly recommend The Trail of the Snail by Arno Brosi.

References:

The following books and websites were used in the creation of this visual guide:
  • Allen J, Humphries T. 2000. Are You a Snail? New York: Kingfisher.
  • Brosi A. The Trail of the Snail. March 24, 2006.
  • Buholzer T. 1987. Life of the Snail. Minneapolis: Carolrhoda Books Inc.
  • Hickman C, Roberts L, Larson A. Integrated Principles of Zoology. McGraw Hill. 2001.
  • Snail. Wikipedia. March 26, 2006.
  • A special thanks to Shutterstock.com and its photographers for the wonderful photos used to illustrate this visual guide. For information about individual image owners, please refer to the copyright information posted just below each photo.




 

Sponges - Phylum Porifera

Sponges - Phylum Porifera

Sponges (Phylum Porifera) are a group of simple aquatic invertebrates that include glass sponges, demisponges, and calcareous sponges. Adult sponges are sessile animals that live attached to hard rocky surfaces, shells, or submerged objects. The larvae are cilliated, free-swimming creatures. Most sponges inhabit marine environments but a few species live in freshwater habitats. 
 

Evidence of Early Sponges Discovered in Oman

Wednesday February 11, 2009
Scientists studying sedimentary rocks in south Oman have discovered high concentrations of steroids that they believe were produced by ancient, multicelluar animals. The team proposes that the fossilized steroids, which date back 635 million years, were produced by sponges, one of the most basic forms of animal life on Earth.
Sponges (Phylum Porifera) are a diverse group of aquatic animals, with about 5000 known species worldwide. Sponges are primarily marine creatures but there are also a few species of freshwater sponges. Sponges are sessile animals that attach themselves to the sea floor and feed by filtering food from the surrounding water.
The discovery of the ancient sponge steroids in Oman suggests that multi-celled animals were present on Earth 100 million years prior to the Cambrian Explosion, a period in our planet's history when animal life diversified rapidly. The steroids that were discovered are of a type present in the cell membranes of sponges. They function to provide the sponge with structural support.
The research team included scientists from University of California, Riverside, Massachusetts Institute of Technology, and other institutions. The study was headed by Gordon Love, an assistant professor of Earth sciences from MIT. Love hopes to focus future study efforts on analyzing sedimentary rocks that are between 850 and 635 million years old. He hopes that by studying these ancient sediments, he and is colleagues will be able to further their understanding of the first multicellular animals to have inhabited Earth.
 

Echinoderms - Phylum Echinodermata

Echinoderms - Phylum Echinodermata

Echinoderms (Phylum Echinodermata) are a diverse group of marine invertebrates comprising approximately 6000 species. Subgroups of echinoderms include starfish, sea lilies, feather stars, brittlestars, sea cucumbers, and sea urchins.

Cnidarians - Phylum CnidariaCnidarians

Cnidarians - Phylum Cnidaria

 

Cnidarians (Phylum Cnidaria) are a group of aquatic animals that includes jellyfish, corals, sea anemones, and hydras. The basic form of the cnidarian body is quite simple and consists of a gastrovascular cavity with a single opening through which food is ingested and waste is released. Cnidarians are radially symmetrical and they have tentacles that encircle their mouth.
The body wall of cnidarians consists of an outer layer or epidermis, an inner layer or gastrodermis, and a middle layer or mesoglea. Cnidarians lack organs and posses a primitive nervous system known as a neural net.
Cnidarians exhibit two basic structural forms, a medusa and a polyp. The medusa form is a free-swimming structure which consists of an umbrella-shaped body (called a bell), a fringe of tentacles that hang from the edge of the bell, a mouth opening located on the underside of the bell, and a gastrovascular cavity.
The polyp is a sessile form which attaches to the sea floor and often forms large colonies. The polyp structure consists of a basal disc that attaches to a substrate, a cylindrical body stalk, inside of which is the gastrovascular cavity, a mouth opening located on the top of the polyp, and numerous tentacles which radiate out from around the edge of the mouth opening.
Most cnidarians are carnivorous and feed on small crustacans. Prey becomes entagled in the tentacles and stinging structures embedded within the tentacles fire barbs and threads into the prey which secrete venom and paralyze the victim. The tentacles then bring the prey into through the mouth into the gastrovascular cavity where it is digested.

Classification:

  • Kingdom: Animalia
  • Phylum: Cnidaria
    The Phylum Cnidaria contains the following subgroups:
    • Class: Cubozoa (sea wasps or box jellyfish)
    • Class: Scyphozoa (cup animals and jellyfishes)
    • Class: Anthozoa (anemones and corals)
    • Class: Hydrozoa (hydrazoans)

    Characteristics:

    Basic Cnidarian Anatomy - Cnidarian Anatomy and Structure

    Basic cnidarian anatomy.
    This assortment of cnidarians show the group's basic anatomical features (radial symmetry, tentacles, and two body forms, polyp and medusa).
    Photos © iStockphoto.
    Cnidarians are diverse and come in many shapes and sizes but there are some basic features of their anatomy that most share in common. Cnidarias have an internal sac for digestion which is called the gastrovascular cavity. The gastrovascular cavity has only one opening, a mouth, through which the animal takes in food and releases waste. Tentacles radiate outward from the rim of the mouth.
    The body wall of a cnidarian consists of three layers, an outer layer known as the epidermis, a middle layer called the mesoglea, and an inner layer referred to as the gastrodermis. The epidermis contains a collection of different types of cells. These include epitheliomuscular cells which contract and enable movement, interstitial cells that give rise to many other cell types such as egg and sperm, cnidocytes which are specialized cells unique to cnidarians which in some cnidarians contain stinging structures, mucus-secreting cells which glandular cells that secrete mucus, and receptor and nerve cells which collect and transmit sensory information.

    Radial Symmetry

    Radial symmetry.
    The radial symmetry of these jellyfish is apparant when they are viewed top-down.
    Photo © Shutterstock.
    Cnidarians are radially symmetrical. This means that their gastrovascular cavity, tentacles, and mouth are aligned such that if you were to draw an imaginary line through the center of their body, from the top of their tentacles through the base of their body, you could then turn the animal about that axis and it would look roughly the same at each angle in the turn. Another way to look at this is that cnidarians are cylindrical and have a top and bottom but no left or right side.
    There are several sub-types of radial symmetry that are sometimes defined depending on the finer structural details of an organism. For example, many jellyfish have four oral arms that extend below their body and their body structure can therefore be divided into four equal parts. This type of radial symmetry is referred to as tetramerism. Additionally, two groups of cnidarians, corals and sea anemones, exhibit six- or eight-fold symmetry. These types of symmetry are referred to as hexamerism and octamerism, respectively.
    It should be noted that cnidarians are not the only animals to exhibit radial symmetry. The echinoderms also display radial symmetry. In the case of the echinoderms, they possess five-fold radial symmetry which is referred to as pentamerism.



  • Medusa

    Medusa.
    These medusa are free-swimming jellyfish.
    Photo © Phdpsx / iStockphoto.
    Cnidarians take on two basic forms, a medusa and a polyp. The medusa form is a free-swimming structure which consists of an umbrella-shaped body (called a bell), a fringe of tentacles that hang from the edge of the bell, a mouth opening located on the underside of the bell, and a gastrovascular cavity. The mesoglea layer of the medusa body wall is thick and jelly-like. Some cnidarians only exhibit the medussa form throughout their life while others first pass through other phases before maturing into the medussa form.
    The medusa form is most commonly associated with adult jellyfish. Although jellyfish pass through planula and polyp stages in their life cycle, it is the medusa form that is most recognized with this group of animals.


  • Polyp

    Polyp colony.
    This closeup of a colony of hydrazoans shows the individual polyps.
    Photo © Tims / Wikipedia.
    The polyp is a sessile form which attaches to the sea floor and often forms large colonies. The polyp structure consists of a basal disc that attaches to a substrate, a cylindrical body stalk, inside of which is the gastrovascular cavity, a mouth opening located on the top of the polyp, and numerous tentacles which radiate out from around the edge of the mouth opening.
    Some cnidarians remain a polyp for their entire life, while others pass through the medusa body form. The more familiar polyp cnidarians include corals, hydras, and sea anemones.



  • Cnidarian Characteristics

    By , About.com Guide

    5 of 10

    Cnidocytes

    The tentacles of cnidarians have cnidocytes embedded within them. The cnidocytes of this jellyfish contain stinging nematocysts.
    Photo © Shutterstock.
    Cnidocytes are specialized cells located in the epidermis of all cnidarians. These cells are unique to cnidarians, no other organism possesses them. Cnidocytes are most concentrated within the epidermis of the tentacles.
    Cnidocytes contain organelles called cnidea. There are several types of cnidea which include nematocysts, spirocysts, and ptychocysts. The most notable of these is the nematocysts. Nematocysts consist of a capsule containing a coiled thread and barbs known as stylets. Nematocysts, when discharged, deliver a stinging venom that serves to paralyze prey and enable the cnidarian to ingest its victim. Spirocysts are cnidea found in some corals and sea anemones that consist of sticky threads and help the animal capture prey and adhere to surfaces. Ptychocysts are found in members of a group of cnidarians known as the Ceriantaria. These organisms are bottom dwellers adapted to soft substrates into which they bury their base. They eject ptychocysts into the substrate which help them establish a secure hold.
    In hydras and jellyfish, the cnidocytes cells have a stiff bristle that projects out from the surface of the epidermis. This bristle is called a cnidocyl (it is not present in corals and sea anemones, which instead possess a similar structure called a ciliary cone). The cnidocyl serves as a trigger to release the nematocyst.





  • Diet and Gas Exchange

    The mouth of a cnidarian.
    The mouth of a cnidarian is located on the top (polyp) or under the bell (medusa) and is surrounded by tentacles.
    Photo © Dang Thang / iStockphoto.
    Most cnidarians are carnivorous and their diet consists mainly of small crustaceans. They capture prey in a rather passive manner—as it drifts through their tentacles the cnidarian discharge stinging nematocysts that paralyze the prey. They use their tentacles to draw the food into their mouth and gastrovascular cavity. Once in the gastrovascular cavity, enzymes secreted from the gastrodermis break down the food. Small hair-like flagella that line the gastrodermis beat, mixing enzymes and food until the meal has been fully digested. Any no-digestable material that remains is ejected through the mouth with a swift contraction of the body.
    Gas exchange takes place directly across the surface of their body and waste is released either through their gastrovascular cavity or by diffusion through their skin.

Jellyfish

Sea Nettle Jellyfish.
Sea Nettle Jellyfish.
Photo © Shooter1247 / iStockphoto.
Jellyfish belong to the Class Scyphozoa. There are approximately 200 species of jellyfish that are subdivided into the following five orders:
  • Order Coronatae
  • Order Rhizostomeae
  • Order Rhizostomatida
  • Order Semaeostomeae
  • Order Stauromedusae
A jellyfish begins its life as a free-swimming planula which after a few days drops to the sea floor and attaches itself to a hard surface. It then develops into a polyp which buds and divides to form a colony. After further development, the polyps shed tiny medusa which mature into the familiar adult jellyfish form which goes on to reproduce sexually to form new planulae and complete their life cycle.
The more familiar species of jellyfish include the Moon Jelly (Aurelia aurita), the Lion's Mane Jelly (Cyanea capillata) and the Sea Nettle (Chrysaora quinquecirrha).

Corals

Mushroom coral.
Mushroom coral.
Photo © Mbz1 / Wikipedia.
Corals belong to a group of cnidarians known as the Class Anthozoa. There are many types of coral and it should be noted that the term coral does not correspond to a single taxonomic class. Some groups of corals include:
  • Order Alcyonacea (soft corals)
  • Order Antipatharia (black corals and thorny corals)
  • Order Scleractinia (stony corals)
Stony corals make up the largest group of organisms within the Class Anthozoa. Stony corals produce a skeleton of calcium carbonate crystals which they secrete from the epidermis of the lower part of their stalk and basal disc. The calcium carbonate they secrete forms a cup (or calyx) in which the coral polyp sits. The polyp can retract into the cup for protection. Stony corals are the key contributors to coral reef formation and as such provide the main source of calcium carbonate for the construction of the reef.
Soft corals do not produce calcium carbonate skeletons like those of stony corals. Instead, the contain tiny cacareous spicules and grow in mounds or mushroom shapes. Black corals are plant-like colonies that form around an axial skeleton that has black thorny structure. Black corals are found primarily in deep. tropical waters.

Sea Anemones

Pink-Tipped Surf Anemone.
Pink-Tipped Surf Anemone.
Photo © Kwerry / iStockphoto.
Sea anemones, like corals, belong to the Class Anthozoa. Within the Class Anthozoa, sea anemones are classified in the Order Actiniaria. Sea anemones remain polyps for their entire adult life, they never transform into the medusa form as jellyfish do.
Sea anemones are capable of sexual reproduction, though some species are hemaphroditic (a single individual has both male and female reproductive organs) while other species have individuals of separate sexes. Egg and sperm are released into the water and the resulting fertilized eggs develop into a planulae larva which attaches themselves to a solid surface and develop into a polyp. Sea anemones can also reproduce asexually by budding new polyps from existing ones.
Sea anemones are, for the most part, sessile creatures which means they remain attached to one spot. But if conditions grow inhospitable, sea anemones can detach from their home and swim off in search of a more suitable location. They can also slowly glide on their pedal disc and can even crawl on their side or by using their tentacles.

Hydrozoa

Flower Hat Jelly (Olindias formosa).
Flower Hat Jelly (Olindias formosa).
Photo © Fred Hsu / Wikipedia.
The Class Hydrozoa includes about 2,700 species. Many hydrozoa are very small and have a plant-like appearance. Members of this group include the hydra and the portuguese man-o-war.
  • Order Actinulida
  • Order Hydroida
  • Order Hydrocorallina
  • Order Siphonophora
  • Order Trachylina



 

 

Arthropods - Phylum Arthropoda

Arthropods - Phylum Arthropoda

Arthropods (Arthropoda) includes insects, spiders, crustaceans, scorpions, and centipedes. Arthropods are bilaterally symmetrical and have segmented bodies. Their body is covered with an exoskeleton and many arthropods have compound eyes.

Readers Respond: What Arthropod Gives You a Fright?

rthropods are a highly successful group of animals. They evolved more than 500 million years ago and are still going strong. But despite their diversity and unconventional beauty, many arthropods can make us jump and scream. From scorpions to spiders to millipedes, what arthropods are most sure to make you go running for the hills?

 

 

Arthropod Pictures:

Cucumber Green Spider

Photo © Pixelman / Shutterstock.
The cucumber green spider (Araniella cucurbitina) is an orb-web spinning spider native to Europe and parts of Asia.

African Yellow Leg Scorpion

Photo © EcoPic / iStockphoto.
The African yellow leg scorpion (Opistophthalmus carinatus) is a burrowing scorpion that inhabits southern and eastern Africa. Like all scorpions, it is a predatory arthropod.

Horseshoe Crab

Photo © ShaneKato / iStockphoto.
The horseshoe crab (Limulus polyphemus) is closer kin to spiders, mites and ticks than it is to other arthropods such as crustaceans and insects. Horseshoe crabs live in the Gulf of Mexico and northward along the Atlantic coast of North America.

Jumping Spider

Photo © Pixelman / Shutterstock.
Jumping spiders (Family Salticidae) are a group of spiders that includes about 5,000 species. Jumping spiders are visual hunters and have acute vision. The are skilled jumpers and secure their silk to the surface before the leap, creating a safety tether.

Lesser Marbled Fritillary

Photo © Shutterstock.
The lesser marbled fritillary (Brenthis ino) is a small butterfly native to Europe. It belongs to the Family Nymphalidae, a group that includes about 5,000 species.

Ghost Crab

Photo © EcoPrint / Shutterstock.
Ghost crabs (Genus Ocypode) are translucent crabs that live on shores around the world. They have very good eye sight and a wide field of vision. This enables them to spot predators and other threats and scurry out of sight quickly.

Katydid

Photo © Cristi Matei / Shutterstock.
Katydids (Family Tettigoniidae) have long antennae. They are often confused with grasshoppers but grasshoppers have short antennae. In Britain, katydids are called bush crickets.

Millipede

Photo © Jason Poston / Shutterstock.
Millipedes (Class Diplopoda) are long-bodied arthropods that have two pairs of legs for each segment, with the exception of the first few segments behind the head which have no leg pairs or only one leg pair. Millipedes feed on decaying plant matter.

Porcelain Crab

Photo © Dan Lee / Shutterstock.
This porcelain crab (Family Porcellanidae) is not really a crab at all. In fact, it belongs to a group of crustaceans that are more closely related to squat lobsters than to crabs. Porcelain crabs have a flat body and long antennae.

Rosy Lobsterette

Photo © / Wikipedia.
The rosy lobsterette (Nephropsis rosea) is a species of lobster that inhabits the Caribbean Sea, Gulf of Mexico and northward to the waters around Bermuda. It inhabits waters of depths between 1,600 and 2,600 feet.

 

 

Ivnvertebrates


Invertebrates

Invertebrates are an extraordinarily diverse group of animals that include over 30 phyla. Invertebrates do not have a backbone, nor a bony skeleton. This large group of animals includes sponges, cnidarians, flatworms, roundworms, segmented worms, molluscs, echinoderms, and arthropods.

10 Facts About Invertebrates

Understanding Animals Without Backbones

 

Invertebrates are one of the six basic groups of animals. Katydids, spiders, sea squirts, octopuses, earthworms, starfish, beetles, hydras, dragonflies, sponges, corals, snails, and jellyfish are a handful of the invertebrates alive today. There are many more. In fact, there are far more living species of invertebrates—animals that lack a backbone—than there are backboned animals (vertebrates).
The term invertebrate does not correspond to a true taxonomic class the way the terms "bird" or "mammal" do. Instead it is an informal term that refers to any taxonomic class of spineless animals: sponges, cnidarians, flatworms, molluscs, arthropods, insects, segmented worms and echinoderms, to name some of the better known groups.
1. The term "invertebrate" refers to an informal collection of a very large number of animals.
Although vertebrates all fall within a single taxonomic group, invertebrates occupy more than 30 groups of animals. These include sponges, cnidarians, flatworms, molluscs, arthropods, insects, segmented worms, and echinoderms as well as numerous minor phyla such as brachiopods, arrow worms, bryozoans, hemichordates, peanut worms, rotifers, water bears, ribbon worms, velvet worms, spoonworms, horseshoe worms and a handful of others.
2. Invertebrates were the first animals to evolve.
The first animals had soft bodies and for this reason they left little fossil evidence of their existence. Scientists have discovered fossilized burrows and tracks in sediments that date back nearly 1 billion years. The oldest fossil of an invertebrate dates back to the late Precambrian, about 600 million years ago.
3. The first invertebrates evolved from single-celled, food-eating microorganisms.
Scientists are still uncertain exactly how the first invertebrates evolved. Most experts agree that the first invertebrates evolved from single-celled, food-eating microorganisms. Scientists think that these microorganisms formed permanent symbiotic groups and in doing so, they were no longer single-celled, they had become multicellular. When this happened, animals had evolved.
4. Invertebrates are often most noted for what they lack: a backbone and a bony skeleton.
Invertebrates do not have bones, a bony skeleton, or a backbone. Instead, they gain structural support for their bodies in different ways. For example, sea anemones have a hydrostatic skeleton that produces support via sheets of muscles and an internal cavity filled with fluid. Other invertebrates such as insects and crustaceans have a hard outer shell or exoskeleton.
5. Invertebrates account for 97 percent of all known species.
An estimated 97% of all species are alive today are invertebrates. Of all invertebrates, the insects are by far the most numerous. There are so many species of insects that scientists have yet to discover them all, let alone name or count them. Estimates of the total number of insect fall in the range of 1 to 30 million. There are also some 10,000 species of sponges, 9,000 species of cnidarians, 100,000 species of mollusks, and 75,000 species of arachnids in addition to tens of thousands of species belonging to other lesser known groups.
6. The simplest invertebrates, in fact the simplest animals, are sponges.
Sponges are sessile animals that live in marine and freshwater habitats. Sponges feed by siphoning water into their body and filtering out food particles. Water enters their body through small pores ou their outer surface. The water then passes into a central cavity and is expelled through a large opening called the osculum. Although the cells in the body of a sponge perform specialized functions, they are not organized into true tissues or organs as they are in other animals.
7. Most invertebrates change form as they grow, going through a process known as metamorphosis.
Metamorphosis is a process by which organisms change form as they mature. Young are sometimes very different from adult forms and may feed on different resources and inhabit different niches. Metamorphosis can enable a species to disperse with greater ease at certain times during its life cycle, find different food resources, or prepare for breeding. The changes involved in metamorphosis are controlled by hormones and may proceed quickly or gradually.
8. Some species of invertebrates form large colonies.
Colonies are groups of animals of the same species that remain together throughout most of their life cycle. Members of a colony are often closely related and benefit from living together by dividing up the work of obtaining food, protecting themselves, and reproducing. Invertebrate colonies are most common in marine habitats where the members of the colony are often physically joined. Marine invertebrate colonies include corals, hydrozoans, Portuguese man-of-war, and sea squirts. Invertebrate colonies that occur on land have individuals that are separated. The best known terrestrial colonial invertebrates are the social insects—bees, ants, termites, and wasps.
9. Invertebrates will eat almost anything that was or is alive.
There are herbivores, carnivores, and detritivores in the invertebrate world. They go about obtaining food in a multitude of ways. Some aquatic invertebrates such as sponges are filter feeders while others such as starfish actively hunt prey. On land, spiders build elaborate webs that snare their prey. Leaf-cutter ants slice and dice foliage from trees and cart it back to their nest where they use it as fertilizer to grow great fungal gardens that feed their colony.
10. Many of the world's parasites are invertebrates.
Ticks, tapeworms, leeches, and roundworms are just a few of the parasites in the animal kingdom and all are invertebrates. Some parasites live on the external surfaces of their hosts while others live in the digestive tract or tissues of their hosts. Parasites often go through an elaborate series of steps in their life cycle during which time they may pass from one to several other hosts.

Animal classification is a matter of sorting out similarities and differences, of placing animals in groups and then breaking those groups apart into subgroups. The whole endeavor creates a structure—a hierarchy in which the large high-level groups sort out bold and obvious differences, while the low-level groups tease apart subtle, almost imperceptible, variations. This sorting process enables scientists to describe evolutionary relationships, identify shared traits, and highlight unique characteristics down through the various levels of animal groups and subgroups.
Among the most basic criteria by which animals are sorted is whether or not they possess a backbone. This single trait places an animal into one of just two groups: the vertebrates or the invertebrates and represents a fundamental division among all animals alive today as well as those that have long ago disappeared. If we are to know anything about an animal, we should first aim to determine whether it is an invertebrate or a vertebrate. We'll then be on our way to understanding its place within the animal world.

What are Vertebrates?

Vertebrates (Subphylum Vertebrata) are animals that possess an internal skeleton (endoskeleton) that includes a backbone made up of a column of vertebrae (Keeton, 1986:1150). The Subphylum Vertebrata is a group within the Phylum Chordata (commonly called the 'chordates') and as such inherits the characteristics of all chordates:
  • bilateral symmetry
  • body segmentation
  • endoskeleton (bony or cartilaginous)
  • pharyngeal pouches (present during some stage of development)
  • complete digestive system
  • ventral heart
  • closed blood system
  • tail (at some stage of development)
In addition to the traits listed above, vertebrates possess one additional trait that makes them unique among chordates: the presence of a backbone. There are a few groups of chordates that do not possess a backbone (these organisms are not vertebrates and are instead referred to as invertebrate chordates).
The animal classes that are vertebrates include:
  • Jawless fish (Class Agnatha)
  • Armored fish (Class Placodermi) - extinct
  • Cartilaginous fish (Class Chondrichthyes)
  • Bony fish (Class Osteichthyes)
  • Amphibians (Class Amphibia)
  • Reptiles (Class Reptilia)
  • Birds (Class Aves)
  • Mammals (Class Mammalia)

What are Invertebrates?

 

Invertebrates are a broad collection of animal groups (they do not belong to a single subphylum like the vertebrates) all of which lack a backbone. Some (not all) of the animal groups that are invertebrates include:
  • Sponges (Phylum Porifera)
  • Jellyfish, hydras, sea anemones, corals (Phylum Cnidaria)
  • Comb jellies (Phylum Ctenophora)
  • Flatworms (Phylum Platyhelminthes)
  • Molluscs (Phylum Mollusca)
  • Arthropods (Phylum Arthropoda)
  • Segmented worms (Phylum Annelida)
  • Echinoderms (Phylum Echinodermata)

Fishes

Fishes

Fishes are a highly diverse group of vertebrates. They include the cartilaginous fishes (sharks, skates, rays, chimera), the ray-finned fishes (paddlefishes, spoonfishes, pipefishes, seahorses, sturgeons, to name just a few), and the lobe-finned fishes (coelacanths and lungfishes).

10 Facts About Fish

Fish are one of the six basic groups of animals. Fish are cold-blooded, aquatic animals that have scales, gills and fins. They were the first backboned animals to evolve and are today the most diverse of all vertebrate groups. The earliest known fish were the ostracoderms, a now-extinct group of jawless fish that appeared in the Cambrian Period, about 510 million years ago. fish include animals such as sharks, skates, rays, chimera, paddlefish, herrings, lanternfish, sea dragons, cavefish, spoonfish, pipefish, seahorses, sturgeons, coelacanths and lungfish to name just a few.
1. Fish are divided into three basic groups which include cartilaginous fish, bony fish, and lobe-finned fish.
Cartilaginous fish (Class Chondrichthyes) are so named because instead of bony skeletons, their body frame consists of cartilage. Tough and flexible, cartilage provides enough structural support to enable these fish to grow to incredible sizes. Cartilaginous fish include sharks, rays, skates and chimaeras.
Ray-finned fish (Class Actinopterygii) are the most diverse of the three groups of fish. The group includes mor than 23,000 species such as salmon, trout, lanternfish, cavefish, cods, anglerfish, tarpon, herrings, electric eels and many others. In contrast to cartilaginous fish, the skeleton of ray-finned fish is composed of true bone.
Lobe-finned fish (Class Sarcopterygii) are a group of bony fish that have paired fins that are at their base fleshy lobes. Ancient lobe-finned fish are thought to be the ancestors of the first four-legged land vertebrates or tetrapods. Modern lobe-finned fish include lungfish and coelacanths.
2. Fish were the first animals to evolve backbones.
The earliest known fish were the ostracoderms, a now-extinct group of jawless fish that appeared in the Cambrian Period, about 510 million years ago. These primitive fish had a notochord but no jaw bones or teeth. Other early fish-like animals include the conodonts and the agnanthans (the hagfish and the lamprey).

3. The ray-finned fish are the largest group of fish.
There are nearly 24,000 species of ray-finned fish which are divided into 431 families.

4. Some species of fish migrate between freshwater and marine environments to spawn.
Such species are referred to as diadromous. They are further described by the direction of their migration. Fish that migrate from the sea into freshwater rivers to spawn (for example, salmon) are described as anadromous. Fish that migrate from a freshwater environment to the sea to spawn (for example, freshwater eels) are described as catadromous.

5. Fish move by creating a wave motion that moves the length of its body.
This wave motion begins at the head and moves to the tale where the resulting side to side motion produces thrust to move the fish through the water.

6. Fish are cold-blooded (ectothermic) animals.
Their internal body temperature is therefore the same as the surrounding water.

7. Many species of cichlids brood their eggs in their mouth.
After the eggs hatch the parent continues to use their mouth to provide shelter for their young.

8. There are two groups of jawless fish alive today.
Once a diverse group of fish that appeared over 500 million years ago, jawless fish are today represented only by lampreys and hagfish.

9. Cartilaginous fish include the sea's largest and most skilled marine predators.
These include sharks, skates, rays, and chimeras. These fish have skeletons made from cartilage, not bone. The cartilaginous skeletons are more flexible than bone.

10. The lateral line system on some fish detects variations in water pressure.
This helps fish detect prey and avoid predators.

 

The 3 Basic Fish Groups

An Introduction to the Main Fish Groups

2. Ray-finned Fishes

Ray-finned fish (Class Actinopterygii) are the most diverse of the three groups of fish. The group includes mor than 23,000 species such as salmon, trout, lanternfish, cavefish, cods, anglerfish, tarpon, herrings, electric eels and many others. In contrast to cartilaginous fish, the skeleton of ray-finned fish is composed of true bone.

3. Lobe-finned Fish

Lobe-finned fish (Class Sarcopterygii) are a group of bony fish that have paired fins that are at their base fleshy lobes. Ancient lobe-finned fish are thought to be the ancestors of the first four-legged land vertebrates or tetrapods. Modern lobe-finned fish include lungfish and coelacanths.
 

Lobe-finned Fishes - Class Sarcopterygii

 

Lobe-finned Fishes - Class Sarcopterygii.
Photos courtesy Wikipedia.
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  Lobe-finned fishes (Class Sarcopterygii) are a group of bony fishes that have paired fins that are at their base fleshy lobes. They are one of two main groups of vertebrates, the other being the Class Arctinopterygii, commonly known as the ray-finned fishes. Lobe-finned fishes hold special interest to evolutionary biologists because members of this group are thought to have given rise to the first four-legged land vertebrates (tetrapods). Modern lobe-finned fishes include lungfishes and coelacanths.

Global Warming Could Be Linked to Dwindling Fish Stocks

Friday January 11, 2002
Scientists are investigating what role climate change plays in the decline of fish stocks throughout the North Atlantic. Previously, overfishing has been cited as the primary reason for dwindling fish stocks but now scientists are investigating another, potentially greater threat that could be contributing to stock decline.
Zooplankton levels have fallen by 90 percent during the last 40 years (National Geographic). And because it provides a vital food source for many fish species including cod and haddock, declining zooplankton could be responsible for the recently observed population crashes in fish stocks.
Plankton are microscopic organisms that drift on the oceans' currents. They include organisms such as diatoms, dinoflagillates, krill, and copepods as well as the microscopic larva of crustaceans, sea urchins, and fish. Plankton also include tiny photosynthetic organisms that are so numerous and productive that they are responsible for generating more oxygen than all other plants on Earth combined.
Plankton are categorized into the following groups based on their trophic role (the role they play within their food web):
  • phytoplankton - Phytoplankton are the primary producers of the planktonic world. They are photosynthetic plankton and include organisms such as diatoms, dinoflagellates, and cyanobacteria.
  • zooplankton - Zooplankton are the consumers of the planktonic world. As such, they feed on other plankton to obtain the energy and nutrients they need to survive. Zooplankton include the larvae of fish, crustaceans.
  • bacterioplankton - Bacterioplankton are the recyclers of the planktonic world. They are free-floating bacteria and archaea that serve to break-down and recycle waste material in the seas.
Plankton can also be categorized by whether or not it spends its entire life as a microscopic organism:
  • holoplankton - Holoplankton are organisms that are planktonic for the entirety of their life cycle.
  • meroplankton - Meroplankton are organisms that are planktonic for only part of their life cycle, for example, only during the larval stage of their development.
Zooplankton and phytoplankton together form the basis of many marine food webs, so if they experience a decline, it will be reflected further up the food chain. If global warming is indeed affecting levels of plankton in the world's oceans, it could mean there will be far reaching effects felt at every trophic level in the oceans' food webs.

 

 

Birds

10 Facts About Birds

Facts About Our Feathered Friends

Birds (Class Aves) are one of the six basic groups of animals. Birds, best known for their ability to fly, are unmatched in their command of the skies. Albatrosses glide long distances over the open sea, hummingbirds hover motionless in mid-air, and eagles swoop down to capture prey with pinpoint accuracy. But not all birds are aerobatic experts. Some species such as kiwis and penguins, lost their ability to fly long ago in favor of lifestyles suited more for land or water.

Although there are numerous different classification systems for birds, on this website, we recognize that there are 29 groups of birds, though this is by no means the only manner in which birds have been classified. Of all the groups of birds, the one group that contains the most species is the Passeriformes, also known as the perching birds.
2. There are 9,865 species of birds alive today, according to the IUCN.
Of the 9,865 bird species, 1,227 species are considered threatened with extinction, 838 species are near threatened, 7,735 species are considered to be of least concern, and 65 species lack the data to determine their status. 133 species of birds are known to have gone extinct since 1500. There are also four species of birds that are classified as extinct in the wild. The last living members of those species survive only in captivity.
3. The earliest known bird, Archaeopteryx lithographica, lived about 150 million years ago during the Jurassic Period.
Archaeopteryx possessed a blend of reptilian and avian characteristics. It had feathers and wings but instead of a bill it had a reptilian snout. Archaeopteryx did not have a keeled breastbone, a key feature for flight, so scientists are uncertain whether it was capable of true flight or if it merely glided. A total of ten Archaeopteryx fossil specimens have been unearthed over the years. All of these fossils were recovered from the limestone deposits in quaries near Solnhofen, Germany. The first Archaeopteryx skeleton, now known as the "London Specimen", was discovered in 1861.
4. Evolutionary biologists remain uncertain as to the origin of birds.
The fossil record for early birds lacks suffcient detail for evolutionary biologists to determine with much certainty which group of reptiles gave rise to birds. Research currently supports the view that birds evolved from a group of dinosaurs known as theropods during the Mesozoic Era. Modern birds share many characteristics with theropods. Both have hollow bones, a pelvis bone that points backward, a wishbone, and a three-toed foot.
5. Feathers are unique to birds.
Feathers are a defining characteristic of the group, meaning simply that if an animal has feathers, then it is a bird. Feathers serve many functions in birds but most notable is the critical role feathers play in enabling birds to fly. In addition to helping to enable flight, feathers also provide protection from the elements. Feathers provide birds with waterproofing and insulation and even block harmful UV rays from reaching birds' skin.
6. Birds are not the only animals that are capable of flight.
Flight is not a characteristic restricted to birds. Bats, which are mammals, fly with great agility and insects, which are arthropods, were fluttering through the air several million years before birds took to the wing.
7. All birds reproduce by laying eggs.
Eggs vary in size and color depending on species. Although there is a wide range of egg colors, only two pigments contribute to the color of the shell. The first pigment is derived from hemoglobin and the second from bile. Most species lay their eggs in a nest. Nests may vary in size, shape, and construction material, but the most common nest shape is cup-shaped.
8. Many birds undertake seasonal migrations between their breeding and wintering grounds.
Many species of birds migrate to high latitudes to breed during the spring and summer. Then during the fall and winter months they migrate to regions of lower latitude. Many species follow similar routes each year when migrating. These routes are referred to as migratory flyways.
9. Birds do not have teeth.
Instead they have bills that are made of the protein keratin. Bird bills come in a variety of shapes and sizes and are adapted to the particular diet of each species. Herons, for example, have a sharp, pointed bill that enable them to capture fish. Finches on the other hand have a short, conical bill that is well-suited for cracking open seeds (Burnie and Wilson 2001, 261).
10. The largest of all birds is the ostrich.
Ostriches are flightless birds that have a large body, small head, long legs, and a long neck. Although they cannot fly, they are remarkable runners, able to run at speeds of up to 45 mph for half an hour. Adult ostriches weigh between 220 and 350 pounds and measure between 7 and 9 1/4 feet in height.


Bird
Definition: A bird is an animal that belongs to the Class Aves. Birds are a diverse group of vertebrates that evolved from reptiles during the Mesazoic Era about 150 million years ago. Today, an estimated 300 billion birds belonging to more than 9000 species inhabit virtually every terrestrial habitat on the planet (Gill 1990). There are even many species of birds that are at home in the water as skilled swimmers and divers. Birds range in size from the massive Ostrich (Struthio camelus) to the minute Bee Hummingbird (Mellisuga helenae). Birds, best known for their ability to fly, are unmatched in their command of the skies. Albatrosses glide long distances over the open sea, hummingbirds hover motionless in mid-air, and eagles swoop down to capture prey with pinpoint accuracy. But not all birds are aerobatic experts. Some species such as kiwis and penguins, lost their ability to fly long ago in favor of lifestyles suited more for land or water.
Birds are the only group of animals to posess feathers. Feathers are used in flight but also provide birds with other benefits such as temperature regulation and coloration (for display and camouflage purposes). Feathers are made of a protein called keratin, a protein that is also found in mammalian hair and reptilian scales.

Characteristics of Birds

Feathers, Furculas, and More

Birds are an amazing and diverse group of animals. Birds, best known for their ability to fly, are unmatched in their command of the skies. Albatrosses glide long distances over the open sea, hummingbirds hover motionless in mid-air, and eagles swoop down to capture prey with pinpoint accuracy. But not all birds are aerobatic experts. Some species such as kiwis and penguins, lost their ability to fly long ago in favor of lifestyles suited more for land or water.
Birds are vertebrates, which means that they are among those animals that posess a backbone. They range in size from the minute Cuban Bee Hummingbird (Calypte helena) to the grand Ostrich (Struthio camelus). Birds are endothermic and on average, maintain body temperatures in the range of 40°C-44°C (104°F-111°F), though this varies among species and depends on the activity level of the individual bird.
Birds are the only group of animals to posess feathers. Feathers are used in flight but also provide birds with other benefits such as temperature regulation and coloration (for display and camouflage purposes). Feathers are made of a protein called keratin, a protein that is also found in mammalian hair and reptilian scales.
The digestive system in birds is simple but efficient (enabling them to pass food through their system quickly to minimize the extra weight of undigested food and the time it takes to extract energy from their food). Food travels through the parts of a bird's digestive system in the following order before it is excreted:
  • esophagus - narrow tube that carries food to the crop
  • crop - a sack-like widening of the digestive tract where food can be stored temporarily
  • proventriculus - the first chamber of a bird's stomach where food is broken down by digestive enzymes
  • gizzard - the second chamber of a bird's stomach where food is ground up by muscular action and small stones or grit (ingested by the birds)
  • intestines - tubes that continue to extract nutrients from food after it has passed through the gizzard

 

10 Facts About Birds

Facts About Our Feathered Friends

Birds (Class Aves) are one of the six basic groups of animals. Birds, best known for their ability to fly, are unmatched in their command of the skies. Albatrosses glide long distances over the open sea, hummingbirds hover motionless in mid-air, and eagles swoop down to capture prey with pinpoint accuracy. But not all birds are aerobatic experts. Some species such as kiwis and penguins, lost their ability to fly long ago in favor of lifestyles suited more for land or water.
1. Birds are divided into 29 groups.
Although there are numerous different classification systems for birds, on this website, we recognize that there are 29 groups of birds, though this is by no means the only manner in which birds have been classified. Of all the groups of birds, the one group that contains the most species is the Passeriformes, also known as the perching birds.
2. There are 9,865 species of birds alive today, according to the IUCN.
Of the 9,865 bird species, 1,227 species are considered threatened with extinction, 838 species are near threatened, 7,735 species are considered to be of least concern, and 65 species lack the data to determine their status. 133 species of birds are known to have gone extinct since 1500. There are also four species of birds that are classified as extinct in the wild. The last living members of those species survive only in captivity.
3. The earliest known bird, Archaeopteryx lithographica, lived about 150 million years ago during the Jurassic Period.
Archaeopteryx possessed a blend of reptilian and avian characteristics. It had feathers and wings but instead of a bill it had a reptilian snout. Archaeopteryx did not have a keeled breastbone, a key feature for flight, so scientists are uncertain whether it was capable of true flight or if it merely glided. A total of ten Archaeopteryx fossil specimens have been unearthed over the years. All of these fossils were recovered from the limestone deposits in quaries near Solnhofen, Germany. The first Archaeopteryx skeleton, now known as the "London Specimen", was discovered in 1861.
4. Evolutionary biologists remain uncertain as to the origin of birds.
The fossil record for early birds lacks suffcient detail for evolutionary biologists to determine with much certainty which group of reptiles gave rise to birds. Research currently supports the view that birds evolved from a group of dinosaurs known as theropods during the Mesozoic Era. Modern birds share many characteristics with theropods. Both have hollow bones, a pelvis bone that points backward, a wishbone, and a three-toed foot.
5. Feathers are unique to birds.
Feathers are a defining characteristic of the group, meaning simply that if an animal has feathers, then it is a bird. Feathers serve many functions in birds but most notable is the critical role feathers play in enabling birds to fly. In addition to helping to enable flight, feathers also provide protection from the elements. Feathers provide birds with waterproofing and insulation and even block harmful UV rays from reaching birds' skin.
6. Birds are not the only animals that are capable of flight.
Flight is not a characteristic restricted to birds. Bats, which are mammals, fly with great agility and insects, which are arthropods, were fluttering through the air several million years before birds took to the wing.
7. All birds reproduce by laying eggs.
Eggs vary in size and color depending on species. Although there is a wide range of egg colors, only two pigments contribute to the color of the shell. The first pigment is derived from hemoglobin and the second from bile. Most species lay their eggs in a nest. Nests may vary in size, shape, and construction material, but the most common nest shape is cup-shaped.
8. Many birds undertake seasonal migrations between their breeding and wintering grounds.
Many species of birds migrate to high latitudes to breed during the spring and summer. Then during the fall and winter months they migrate to regions of lower latitude. Many species follow similar routes each year when migrating. These routes are referred to as migratory flyways.
9. Birds do not have teeth.
Instead they have bills that are made of the protein keratin. Bird bills come in a variety of shapes and sizes and are adapted to the particular diet of each species. Herons, for example, have a sharp, pointed bill that enable them to capture fish. Finches on the other hand have a short, conical bill that is well-suited for cracking open seeds (Burnie and Wilson 2001, 261).
10. The largest of all birds is the ostrich.
Ostriches are flightless birds that have a large body, small head, long legs, and a long neck. Although they cannot fly, they are remarkable runners, able to run at speeds of up to 45 mph for half an hour. Adult ostriches weigh between 220 and 350 pounds and measure between 7 and 9 1/4 feet in height.


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Nestling

Definition: (noun) A young, recently hatched bird that has not yet grown any flight feathers and is unable to fly. They may lack feathers entirely or could be covered with a light down, depending on the species. Nestling birds are entirely dependent on their parents for food and protection, though the length of that dependency varies for each bird species from just a few days to several weeks. One or both parents may feed the young birds and stay with them to help regulate their body temperature until they acquire thicker plumage.
As birds mature and begin to grow their adult flight feathers, they are no longer called nestlings and instead are referred to as fledglings.
Pronunciation: NEST-leeng
Also Known As: Baby Bird (noun), Hatchling (noun), Chick (noun)
 
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