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General Characteristics of the Phylum Cnidaria
Characteristic of this phylum is that these organisms' bodies are organized around a central point, a feature known as radial symmetry. When you observe an anemone, you notice that its tentacles are organized in a circle surrounding its mouth. If a radially symmetrical organism were cut like a pie, each slice should have similar parts. While cnidarians do not have brains, they have a very primitive nervous system. When one part of the animal is stimulated, the entire animal reacts through its nerve net.
Classification of Phylum Cnidaria

Class Scyphozoa (sky-pho-ZO-uh)

This class includes the jellyfish, which are found all over the world from polar to tropical seas. They are most common in tropical and subtropical waters. Jellyfish, of course, are mis-named-they are not fish, but invertebrates. Between the two cell layers, Scyphozoans have a jelly-like substance called mesoglea, which has a low density and allows the animals to float. Scyphozoans are characterized by their umbrella shape, called a medusa. The medusa contracts and expands, allowing the jellyfish to move, but because of its inability to move against ocean processes like currents and tides, jellyfish are still considered to be zooplankton. While it is mostly the tentacles that capture prey, the medusa is often sticky, catching plankton and other small organisms.

Class Cubozoa

The cubozoans, or "box jellies," are named for their cubic shape, observable when viewed from above. Once classified as scyphozoans, these organisms have more recently been classified into a new class due to differences in structures during their life cycle. In addition, cubozoans are strong swimmers and often contain nasty venom that can be deadly to humans. Despite having only a nerve net, like all cnidarians, cubozoans have complex eyes.

Class Anthozoa (an-tho-ZO-uh)

Anthozoans include sea anemones and corals. Their body structure can be likened to an upside-down jellyfish, with the mouth and tentacles facing up. This body form is called a polyp.

Sea anemones attach to substrates using a muscular foot. They use their nematocysts to stun prey, and tentacles to move prey into the mouth. Anemones are often recognized for their symbiotic relationship with fish, which live among their tentacles.

Unlike sea anemones, corals live in large groups that are attached to one another. They are colonial organisms. Each individual coral polyp looks similar to a sea anemone, but is connected to other members of the colon by a thin membrane through which nutrients and other substances are shared.

Class Hydrozoa (high-dro-ZO-uh)

Hydrozoans are a very diverse group of invertebrates. This class includes organisms like the freshwater hydra, colonial hydroids, and jellyfish-like organisms such as the Portuguese Man of War. Colonial hydrozoans are often mistaken for plants or algae, and have a feathery or flowery appearance. They grow on substrates such as rocks, piers, and the shells of mollusks or arthropods.

Examples:
Jellyfish, Anthozoa, Sea anemone

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General Characteristics of the Phylum Annelida
Annelids have a one-way digestive tract, in which food passes in one direction, in through the mouth and out through the anus. These worms exhibit bilateral symmetry, which means that their left and right sides are very similar. Many annelids have both male and female sex organs; they are hermaphrodites.
Classification of Phylum Annelida

Polychaeta - these organisms are found in the marine environment and include free-swimming and worms that live in tubes.

Hirudinea - leeches, which normally have a sucker on their mouth, with which they grab onto prey. Leeches prey on a wide variety of organisms including snails, fish, and even humans.

Oligochaeta - includes earthworms and their aquatic relatives, such as sandworms.

Pogonophora - "beard worms," which include the giant tube worms found in the deep sea near hydrothermal vents. Once considered their own phylum, most scientists now classify these worms as a class within Phylum Annelida.

Examples:
Earthworm, Oligocheate, Polychaete

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General Characteristics of the Phylum Nematoda

The phylum Nematoda are commonly called roundworms and have unsegmented bodies and a layer of cuticle that is secreted by the hypodermis underneath the skin. Nematodes lack a coelum and instead have a small, fluid-filled cavity containing their reproductive organs and intestine.
Classification of Phylum Nematoda

Phylum - Aschelminthes

Class - Nematoda

Class - Nematomorpha

Class - Rotifera

Class - Gastrotricha

Class - Kinorhyncha

Examples:
Ascaridida, Secernentea, Chromadorea,

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General Characteristics of the Platyhelminthes
1)Bilaterally symmetrical.
2)Body having 3 layers of tissues with organs and organelles.
3)Body contains no internal cavity.
4)Possesses a blind gut (i.e. it has a mouth but no anus)
5)Has Protonephridial excretory organs instead of an anus.
6)Has normally a nervous system of longitudinal fibres rather than a net.
7)Generally dorsoventrally flattened.
8)Reproduction mostly sexual as hermaphrodites.
9)Mostly they feed on animals and other smaller life forms.
10)Some species occur in all major habitats, including many as parasites of other animals.
Classification of Platyhelmintes
Class Turbellaria
Class Monogenea
Class Trematoda
Class Cestoda

Examples:
Tape worms, Flukes, Turbellaria, Monogenea

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General Characteristics of the Echinoderms
The skin covers an internal skeleton. Like cnidarians (e.g., jellyfish and corals), the bodies of echinoderms are organized around a central point; they exhibit radial symmetry. Interestingly, their larvae are not radially symmetrical-they have a left and right side, or bilateral symmetry. The radial symmetry of echinoderms is five-parted, meaning that if an organism were sliced like a pizza in five slices, each slice would look similar and contain similar features. This five-part symmetry is very unique.

Another unique characteristic of echnioderms is a network of water-filled tubes called a water vascular system

Classification of Echinoderms

Class Asteroidea - (ast-er-OY-dee-uh)- This class includes the sea starts, which are often incorrectly called starfish. Of course, they are not fish, but invertebrates. Sea stars have five or more arms that radiate from a central disk. In most sea stars, if an arm is cut off and includes part of the central disk, the organism can regenerate itself. Although they are slow-moving, most sea stars are predators, preying upon mollusks like clams and mussels by using their tube feet to pry the animal's shells apart. They then eject their stomach through their mouth into the mollusk-digesting it externally!

Class Ophiuroidea (oh-fee-uh-ROY-dee-uh) includes the brittle and basket stars. They are similar in appearance to true sea stars, but have long, thin arms that often have feathery projections. Those projections help the animals to capture particles, such as phytoplankton and zooplankton, suspended in the water. Brittle and basket starts tend to be filter feeders.

Class Echinoidea (eck-in-OY-dee-uh) includes the sea urchins and sand dollars. Many species of sea urchins are voracious grazers of kelp and other seaweeds, using their well-developed sharp mouthparts. Most have long spines that extend from their internal skeleton, often called a shell or test.

Class Holothuroidea (ho-lo-thoo-ROY-dee-uh) includes the sea cucumbers. These echinoderms are elongated and sausage-shaped, and use tube feet to move along the bottom. Most are detritus feeders. The spines of these echinoderms are much smaller than their cousins, the sea stars and sea urchins.

Class Crinoidea (cry-NOY-dee-uh) - The crinoids include the feather stars and sea lilies, and are often mistaken for plants. These are the most ancient of the echinoderms; dominating the fossil record from the Paleozoic Era, from about 570 to 225 million years ago. Many of these organisms have stalks with which they attach to the substrates.

Examples:
Sea star , Sea urchin, Sea cucumber

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General Characteristics of the Molluscs

1. Unsegmented soft body with bilateral symmetry

2. Presence of an internal or external shell

3. A toothed tongue (made mostly of chitin) called the radula

4. A mantle which is a fold in the body wall that lines the shell

5. Muscular foot (and/or tentacles in some).

6. Possession of a fluid-filled cavity called coelom

Classification of Mollusca

Class Gastropoda - This is the largest group of mollusks, and includes snails, slugs, limpets, and more. Gastropods have different feeding strategies, which range from using their radulas to scrape algae off of rocks to boring holes in bivalves like clams and oysters. Sea slugs, or nudibranchs, are some of the most interesting marine gastropods. Many are poisonous and are brightly colored to warn potential predators.

Class Bivalvia - The term "bivalve," refers to these animals' two shells. This class includes oysters, clams, mussels, scallops and more. Bivalves are found in the ocean and in freshwater. Many use their muscular foot for burrowing, and the gills are typically used for capturing food, as these animals are normally filter feeders. Unlike most mollusks, bivalves do not tend to have a radula.

Class Polyplacophora - This class includes the chitons (KITE-ins), and is named for its overlapping plates that form the animals' shells. Chitons are found in marine environments, mostly along rocky shores.

Class Cephalopoda - Cephalopods are named for their large heads - "cephalo" meaning "head" and "poda" meaning "foot." Members of this class include octopus, squid, cuttlefish and chambered nautiluses. In this class, the characteristic molluscan foot has been modified into arms and tentacles, which are used for feeding and locomotion. Octopuses are considered to be some of the smartest invertebrates, and have a very large brain. Cephalopods tend to have large eyes.

Examples:
Squid, Clam , Oyster

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General Characteristics of the Phylum Arthropoda

They posses a chitinous exoskeleton that must be shed during growth.

The paired appendages (e.g., legs, antennae) are jointed.

The segmented bodies are arranged into regions, called tagmata (e.g., head, thorax, abdomen).

They have bilateral symmetry.

The nervous system is ventral (belly) and the circulatory system is open and dorsal (back).

Classification of Phylum Arthropoda

Subphylum Crustacea - Crustaceans make up the majority of marine arthropods, and are sometimes thought of as the "insects of the sea." They include copepods, lobsters, crabs, krill, shrimp and barnacles. Their exoskeletons are often composed of both chitin and calcium carbonate. Crustaceans have gills to facilitate gas exchange, and have two pairs of antennae with which they sense their environment. Their jointed appendages are specialized for activities that include swimming, crawling, and attaching to other animals.

Subphylum Chelicerata - This group includes the spiders, sea spiders, ticks, mites, scorpions, and horseshoe crabs. Arthropods with specialized mouthparts are classified into this subphylum.

Subphylum Uniramia - Includes the insects (Class Insecta), as well as centipedes and millipedes.

Examples:
Insects, Lobsters, Crabs

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General Characteristics of Porifera

1)No definite symmetry.
2)Body multicellular, few tissues, no organs.
3)Cells and tissues surround a water filled space but there is no true body cavity.
4)All are sessile, (live attached to something as an adult).
5)Reproduce sexually or asexually, sexual reproduction can be either gonochoristic or hermaphroditic.
6)Has no nervous system.
7)Has a distinct larval stage which is planktonic.
8)Lives in aquatic environments, mostly marine.
9)All are filter feeders.
10)Often have a skeleton of spicules.

Classification of Porifera

Calcareous Sponges - have spicules made of calcium carbonate and are generally smaller than other sponges.

Demosponges - have a skeleton comprised of spongin and are the most diverse sponge group.

Glass Sponges - have spicules made of silic.

Examples:

1. Sycon
2. Hyalonema
3. Euplectella
4. Spongilla