Echinodermata

Echinoderms are a large and ancient type of marine animal with about 7,000 living and 13,000 extinct species. This type includes starfish, sea urchins, sea lilies, brittle stars, sea cucumbers and several other small groups. echinoderms have two distinctive features. The first one is which is radial (usually pentaradial) symmetry. The second distinctive feature is the water-vascular or ambulacral system. This is a complex system of channels which are filled with a liquid that is similar to seawater in its composition. it covers the animal’s whole body and is characteristic for all echinoderms. Extensions of the ambulacral system form a set of small feet with suckers that protrude from the animal’s body. The animal can make these extensions stretch and retract by contracting muscular ampoules and changing the pressure of the fluid. This hydraulic mechanism is complex, yet harmonious and it cannot be found in any other group of animals. The creatures use the ambulacral system for movement, respiration, excretion and tactile sensing.

There is an extraordinarily large variety of echinoderms in the World ocean. Many species are strikingly different from one another in shape, colour and lifestyle. There are even deep planktonic sea cucumbers and free-swimming sea lilies. echinoderms range in size from a few millimetres to a few meters (such as the Synapta maculata sea cucumber), and they can live in the deepest parts of the World ocean. However, you can also find many echinoderms on the shore in the littoral zone. Echinoderms also have a wide range of feeding strategies: many are detritivores and get food from the sea floor and soft sediments; some are also omnivorous polyphages, some are predators (most starfish) and some are herbivores (mainly urchins). These creatures live throughout the World ocean, and their biomass and species composition are just as impressive in the cold seas as it is in the warm tropics.