Characters common to all Echinodermata
- They are all deuterostomes (the anus is developed before the mouth - only seen in echinoderms and chordates).
- They have no defined head or brain.
- Possess an endoskeleton (test) composed of porous calcium carbonate plates covered by a thin protoplasmic skin.
- Secondary radial symmetry, most with penta-radial symmetry.
- Unique to the phylum is the water vascular system (WVS) which functions for the locomotion (tube feet), respiration and feeding.
- Also unique to the phylum is a connective tissue called mutable collagenous tissue (MCT).
- Most echinoderms are covered in bumps and spines.
- All have the ability to regenerate parts of their body.
- Only found in steno-haline (true marine) environments, all types are free living.
Unique to Ophiuroidea
- All the viscera (internal organs) are contained within the central disc, the disc is well differentiated from the arms.
- The arms (generally 5) are long and sinuous, up to 60cm
long used to “row” with for locomotion. This allows a
faster movement within the water column.
- They have no anus, all food is taken in, and undigested
food excreted, though the mouth. They cannot turn their stomachs inside
out as seen in star fish.
- The tube feet do not have the suctorial ability of other echinoids, who use suction to move about slowly over surfaces and to prise open the shells of prey.
Author: Lorna O'Brien
Last updated: 19/11/2006
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produced by students
on the MSc
Palaeobiology programme in the Department
of Earth Sciences at the University of Bristol for academic