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Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes(specialized cells that they use mainly for capturing prey)Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes

 Mollusca_19.gif Mollusca are highly diverse: in size; in anatomical structure; in behaviour and in habitat.The phylum is typically divided into nine or ten taxonomic classes.The gastropods (snails and slugs) include by far the most classified species, accounting for 80% of the total. Cephalopod molluscs such as squid, cuttlefish and octopus are among the most neurologically advanced invertebrates.
Molluscs have diverse body structures. The two most universal characteristics are a mantle with a significant cavity used for breathing and excretion, and the structure of the nervous system.
Echinodermata_3.gif Echinodermata are a unique group of exclusively marine animals with a peculiar body architecture. They are headless with a fivefold radial symmetry. The body wall contains the endoskeleton, made of numerous independent calcareous plates which frequently support spines.  The spines may protrude through the outer epithelium, and are often used for defense. The skeletal plates of the body wall, together with their associated muscles and connective tissue, form a tough and sometimes rigid test which encloses the large coelom. A unique water-vascular system is involved in locomotion, respiration, food gathering, and sensory perception.
Crustacea_26.gif Crustacea have segmented, chitin-encased bodies; articulated appendages; mouthparts known as mandibles during some stage of their life, however modified they may be for cutting, chewing, piercing, sucking, or licking; and two pairs of accessory feeding organs, the maxillules and maxillae. One or the other pair is sometimes vestigial or may be lacking. The Crustacea are unique in having two pairs of antennae: the first pair, or antennules, and the second pair, the antennae proper. The latter, are almost always functional at some stage of every crustacean's life.
Porifera_18.gif Porifera are animals of the phylum Porifera .Their bodies consist of jelly-like mesohyl sandwiched between two thin layers of cells. While all animals have unspecialized cells that can transform into specialized cells, sponges are unique in having some specialized cells that can transform into other types, often migrating between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, and the shapes of their bodies are adapted to maximize the efficiency of the water flow 
Ascidiacea_5.gif Ascidiacea  is a class in the Urochordata subphylum of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" made of the polysaccharide tunicin, as compared to other tunicates which are less rigid.Sea squirts are sessile animals: they remain firmly attached to substratum such as rocks and shells.Sea squirts feed by taking in water through the oral siphon. The water enters the mouth and pharynx, flows through mucus-covered gill slits into a water chamber called the atrium, then exits through the atrial siphon. 
Bryozoa_37.gif Bryozoan individuals in colonies are called zooids, since they are not fully-independent animals. All colonies contain autozooids, which are responsible for feeding and excretion. Colonies of some classes have various types of non-feeding specialist zooids, some of which are hatcheries for fertilized eggs, and some classes also have special zooids for defense,typically about 0.5 millimetres long, they sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia.
Unsegmented_Worms.gif Marine worms are any worm that lives in a marine environment is considered a marine worm. Marine worms are found in several different phyla, including the Platyhelminthes, Nematoda, Annelida (segmented worms), Chaetognatha, Hemichordata, and Phoronida.These worms have specialized tentacles used for exchanging oxygen and giving out carbon dioxide, plus they are used for reproduction.Some marine worms are tube worms, of which the giant tube worm lives in waters near underwater volcanoes, and can withstand temperatures up to 90 degrees Celsius  

Arthropoda(sea spiders), also called Pantopoda , are marine arthropods . Ranging in size from 1 to 10 millimeters to over 90 centimeters in some deep water species ,most are toward the smaller end of this range in relatively shallow depths.Although "sea spiders" are not true spiders, or even arachnids, their traditional classification as chelicerates would place them closer to true spiders than to other well known arthropod groups, such as insects or crustaceans. 





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