phylum ECHINODERMATA (Klein, 1734)
Holothurians or sea cucumbers
Echinodermata are a highly unique invertebrate group. Among a whole series of their morphological specifics, the following three basic characteristics may be distinguished: (1) five-ray radial symmetry, (2) lime mesoderm skeleton with highly diverse skeletal elements, and (3) ambulacral or water-vascular, coelomic system.
These animals originated from sedate ancestral filtratrator-organisms tending to develop their radial trapping apparatus in the form of feelers, rays, and ciliate fissures. As a support skeleton for protection against predators, Echinodermata acquired a special calcareous frame. In their calcium carbonate skin, porous small bones, needles or plates, capable of linking with one another in a rigid or mobile shell, precipitate. The echinoderm ambulacral system represents a unique hydraulic locomotion system allowing the animals to move and capture food. The ambulacral system communicates with the environment through a special organЧa porous (madreporous) plate, via which the hydrostatic pressure inside and outside the animal equalizes. An annular canal situated around the esophagus, radial canals with numerous sambulacral ampoules along each arm represents the system or ray branching from said annular canal. In many echinoderms, ambulacral legs supplied with suckers and connected with ampoules branch from radial canals. The legs move due to change of cavity pressure in the system ampoules and canals. Echinoderms without legs move with the aid of their shell skeletal elements with actuating muscles.
The life cycle of all echinoderms, except adult benthos forms, includes (plankton) larvae freely swimming deep in the water, likewise highly diversified morphologically in various groups of recent echinoderms.
Today, recent echinoderm world fauna is represented by 6,250 species. The current diversity of this group is considerably less than before, say in Paleozoic. Today, only six of twenty-four classes remain from this formerly vast group of invertebrate animals.
According to our counts, Southern Primorye is inhabited by 74 echinoderm species representing five classes.
A. ADRIANOV, Doctor Sci. (Biology),
of Marine Biology, Far East Branch, Russian Academy of Sciences.