Animals in the Oceans

The Kingdoms

Kingdom Animalia Marine

Phylum Porifera These are sponges which live in clear, shallow ocean waters around the world. The adults are sessile (fixed in place). They are filter-feeders of small microorganisms and bits of organic matter. They are usually hermaphrodites :Each individual produces sperm and eggs. Larvae live as meroplankton.

Phylum Cnidaria Class Hydrozoa live as dense colonies of polyps. The adults are usually sessile and the larvae are meroplankton. Portuguese Man-of-War looks like a jellyfish but is actually a colony. Fish are trapped by special stinging tentacles which poison the prey and digested by the feeding polyps.

Phylum Cnidaria Class Scyphozoa are called jellyfish. The sexes are separate. The larvae are sessile polyps which undergo asexual budding to produce medusae. These medusae mature into adult jellyfish which are drifters (meroplankton). Their mouths are located on the underside surrounded by tentacles.

Phylum Cnidaria Class Anthozoa are the corals and anemones which exist only as polyps. Anemones live in tide pools and shallow coastal waters. Corals are colonial polyps which secrete limestone walls made of calcium carbonate. All can feed with tentacles but most live with symbiotic algae. These form coral atolls (islands) and barrier reefs in warm ocean waters.

Phylum Mollusca This taxon includes the squid, clams, mussels, snails and slugs. There are about 100,000 species. They share a basic body plan: a fleshy foot and mantle and a shell (or its remnants). They range is size from minute to 18 m in length (the giant North Atlantic squid).

Phylum Mollusca Class Polyplacophora are called chitons. Chitons have a shell composed of eight simple plates. These are slow-moving organisms which creep along over the bottom of tide pools and graze on algae as they go.

Phylum Mollusca Class Gastropoda includes snails and their relatives. The name means “stomach foot”. During its development, a snail’s body undergoes torsion (twisting) caused by uneven muscle growth. Some have beautiful shells and others are shell-less such as the nudibranch and slug.

Phylum Mollusca Class Bivalvia have two hinged shells which is closed by powerful muscles. These are mostly filter-feeders using mucus to trap small particles of food from the water. Some bivalves are mussels, scallops, oysters and clams.

Phylum Mollusca Class Cephalopoda include the squid, octopus, cuttlefish and nautilus. The name means “head-foot”. The squid and cuttlefish have a reduced internal shell. All have well developed eyes. They are active predators feeding on fast-moving invertebrates and vertebrates. Their foot is modified into tentacles with suckers and the mouth has a beak for tearing and ripping food. They are the most intelligent invertebrates.

Phylum Annelida Class Polychaeta are segmented marine worms. Some are active swimmers while others live inside burrows and tubes. Most are particle feeders trapping minute plankton and loose material in cilia or mucus-covered tentacles. The sexes are separate releasing eggs and sperm into the water to fertilise. The larvae become part of the meroplankton.

Phylum Arthropoda There are over 900,000 species of arthropods which have been described. About a million more are left to identify. Arthropod means “jointed feet (legs)”. They have exoskeletons, jointed bodies and to grow, they must molt. They are a very successful phylum filling a large variety of niches, and large numbers of offspring.

Subphylum Crustacea Subphylum Crustacea includes crab, lobster, shrimp, copepods and barnacles. Their larvae may have an entirely different diet than the adults. Marine forms are benthos and plankton.

Phylum Arthropoda Trilobites were extinct marine arthropods. Many of the marine forms are very important because microscopic crustaceans compose most of the plankton. Subphylum Chelicerata includes the horseshoe crabs and sea spiders.

Phylum Echinodermata These are the ‘spiny-skinned” animals. The larvae have bilateral symmetry but the adults have a five-part radial construction. They are exclusively marine and brackish (estuarine) water animals. They have numerous tube feet which are moved by hydraulic pressure.

Phylum Echinodermata Class Stelleroidea are seastars (starfish) and brittle stars. They are slow-moving predators which each bivalves such as oysters. The seastar can regenerate any of its arms. An arm, as long as a bit of the central disk is attached, can regenerate the entire animal.

Phylum Echinodermata Class Echinoidea includes the sea urchins and sand dollars. Sea urchins can overgraze areas of the seafloor if not kept in check by their predators. Now sea urchin roe is a sushi delicacy. Other classes include the brittle stars and sea cucumbers.

Phylum Chordata This group of animals is diverse and includes humans. All chordates have gill slits (sometimes only in the embryo), tubular nerve cords, a notochord (in the embryo) and a postanal tail. Members of the subphylum Vertebrata all have backbones.

Phylum Chordata The Class Amphibia contains the frogs, toads and salamanders. There are NO MARINE AMPHIBIANS!

Class Chondrichthyes Class Chondrichthyes includes the sharks and rays whose skeletons are made of cartilage. Fertilization is internal but embryo development varies among species.

Class Osteichthyes Class Osteichthyes means “bony fish”. They are not closely related to sharks and rays. In most bony fish, fertilization is external and large numbers of eggs are released into the environment.

Class Reptilia Class Reptilia includes sea snakes and turtles, marine iquanas and saltwater crocodiles. They are ectothermic. Some lay eggs on land such as the crocodiles and turtles. Sea snakes give birth to live young. They are all air breathing but spend most of their lives in the salt water.

Class Aves These are birds all of which have feathers. They are endothermic. Fertilization is internal and all lay eggs on land. There are a large number of shorebirds which prey on fish and other marine creatures. These include seagulls, ospreys, and the like. Some birds can dive such as cormorants, terns, salt water ducks and penquins.

Class Mammalia These are animals which have hair and produce milk. They are endotherms and are air-breathing. Fertilization is internal and they have live young. Marine mammals include dolphins, porpoises and whales. Seals, sea lions, and walrus are called pinnepeds.