ACS Distance Education UK
GENERAL CHARACTERISTICS OF ANIMALS IN THE PHYLUM ECHINODERMATA
• Around 6000 species: all are marine animals.
• Most occur in relatively shallow water close to shore.
• All have a water vascular system –a series of coelomic tubes filled with water.
• Most have two sexes (rarely hermaphrodite).
• Tube feet appendages are highly characteristic of the phylum.
• The gut structure can vary: it might or might not have an anus; generally there are no special excretory organs.
• The body is usually pent radially symmetrical (ie. when cut in half, it forms five similar sections around a central point as seen clearly with a star fish).
• The nervous system is well developed but mostly over the epidermis or outer layer.
• Special sensory organs are present, but poorly developed.
• The epidermis is ciliated, and covers a calcareous endoskeleton which can often grow out to produce spines, sometimes large.
• Eggs develop inside the body and are born as miniature adults (free-swimming larvae).
• Usually, but not always, the eggs receive no nutrition or metabolic support from the parent, while developing inside the parent’s body.
• There have been 16 classes, though all but six classes of Echinoderms are now extinct.
All animals in the phylum Echinodermata live exclusively in the ocean. There are around 6000 species in the phylum, including starfish, sea cucumbers, sea urchins, brittle stars and crinoids.
The adults have a unique radial symmetry, with structures often repeated in multiples of five; eg. the arms of the starfish. They have a leathery skin which surrounds an internal skeleton of interlocking calcium carbonate plates, known as ossicles.