Class Holothuroidea

Major Attributes:
  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.

Some Interesting Facts:

Pertinent References in Lamson Library:
  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.

(Carianne K. Meyers, Fall 1994; edited by T. Shultz, Spring 1995)