Snails
Phylum – Mollusca
Class – polyplacophora (chitons)
Class – gastropoda (one shelled animals: snails, abalone)
Class – bivalia (two shelled animals: muscles)
Class – cephalopoda (octopus)

Mollusc is a Latin term meaning “soft-bodied”, and these animals are often protected by a hard, protective covering. This phylum makes up an important food source for many marine animals. All molluscas have mantles or underlying skin which produces the shell. They also have siphons or fleshy tubes that draw in food and water. Gills are common organs used to respire by removing oxygen from the water that all molluscas possess.

Spiny Shelled Animals
Phylum – Echinodermata
Class – asteroidea (sea stars)
Class – echinoidea (sea urchins)
Class – holothuroidea (sea cucumbers)

Echinoderm is a Greek word meaning “spiny-skinned.” Animals in this phylum all share a few common characteristics. All echinoderms have an endoskeleton or and internal skeleton made up of ossicles, a type of calcareous structure. The compactness of the ossicles determines the degree of flexibility of the animal. The adult body symmetry radiates around a central axis as well. Echinoderms also have tube feet which they use for locomotion and also for respiration. The tube feet operate using a hydraulic, or water-vascular, system.

Jointed Animals
Phylum – Arthropoda
Class – merostamata (horseshoe crabs)
Class – crustacea (hermit crabs, lobster)

Arthropod is a Greek word meaning “jointed appendage.” With perhaps more than one million known species, this is the largest and most diverse invertebrate phylum. Arthropods make up more than 80% of all animal species. Animals in this phylum share common characteristics including segmented bodies, jointed appendages, and an exoskeleton made of chitin. As it grows, an arthropod must molt, shedding its old exoskeleton.

Phylum – Cnidaria
Class – anthozoa (sea anemonies)

The cnidarians are a diverse group. About 9,000 species are known worldwide, and they are found throughout the seas from densely populated intertidal zones to great depths.
Many cnidarians are large and brightly colored. Some common traits seen among these animals include symmetrical bodies around a central axis. Cnidarians lack a head and usually bear a crown of tentacles around the mouth. In these tentacles, nematocysts or tiny stinging capsules are present to act as a defense mechanism.

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