Class Holothuroidea

1. Lack arms.
2. Bilaterally symmetrical.
3. Body wall soft rather than calcareous.
4. Dioecious with a single gonad.
5. Sedimentary feeders.
6. Body surrounded by tube feet.
7. Interior madreporite.
8. Branched tentacles surrounding mouth that are lined with modified water vascular system.

The holothuroideans, commonly called sea cucumbers, are a very unique group of echinoderms. They are the only class that is soft bodied rather than hard with well-developed circular and longitudinal muscles. Their axis of symmetry is horizontal unlike other echinoderms. The mouth and anus are located at separate ends of the sea cucumber's elongated body. The mouth is surrounded by modified tube feet that form a ring of tentacles. The number of tentacles varies from 8-30 depending on the order. This is one feature that is used to divide this class into smaller groups. Tube feet can be found all over the holothuroidean's body that are usually contracted within the external body wall. Sea cucumbers are sessile and very sluggish. They ingest large amounts of sand and filter out what is not used. Both eggs and sperm are ejected into the water where fertilization takes place. The body wall contains reduced spicules found in shapes of rods, crosses or hooks. The respiratory system takes up most of its internal mass and is found in no other echinoderm.

• Sea cucumbers have the ability to eviscerate parts of, or its entire internal mass to ward off prey. In a least two species, autoeviscerationoccurs on a seasonal basis, but it is not known exactly why.
• Sea cucumbers lack arms unlike other echinoderms. Tentacles have taken their place.
• Respiratory trees evolved and are found in no other echinoderm. These trees are outgrowths of the cloaca.
• Sea cucumbers can live from 5-10 years.
• They are found in all seas at all depths. Some ocean trenches contain more than 90% of the total biomass.
• Sea cucumbers are considered a delicacy in many countries around the world.

1. Barnes, R.S.K., Calow, P., Olive, P.J.W. 1988. The Invertebrates: a new synthesis. Oxford: Blackwell Scientific Publications.
2. Nichols, David. 1962. Echinoderms. London: Hutchinson University Library.
3. Pawson, David L. 1982. Synopsis and Classification of Living Organisms New York: McGraw Hill Book Company.