258 



CHAETOGNATHA THROUGH LOWER CHORDATA: 



CLASS HOLOTHUROIDEA (Sea Cucumbers) 



Diagnosis: body elongate, soft or five-sided, with- 

 out spines, sometimes worm-like, generally cucum- 

 ber-like; mouth surrounded by tentacles; arms 

 absent (Figure 15-2). 



Sea cucumbers live on or under rocks and in or on 

 sand and mud. Plankton are trapped by the mucous- 

 covered tentacles, or bottom debris is taken into the 

 body where the organic matter in the debris is used as 

 food. Some have a posterior group of mucous-covered 

 tubes that are thrust out to entrap food or entangle 

 an enemy. 



Partial self-destruction frequently is the result 

 when the animals are irritated. Some may break off 

 parts of their bodies by violent contractions; others 

 may rupture the body wall, causing organs to be 

 ejected; and some may cast out digestive and respira- 

 tory structures through the anal opening. After such 

 behavior, the castoff parts are regenerated. 



The sexes are usually separate, with fertilization 

 occurring in sea water after the spawning of eggs and 

 sperm. It is common for many to retain the eggs 

 within or upon the body in brood pouches. 



Sea cucumbers are of little direct use to man in our 

 country. However, in the Orient and South Pacific, 

 the boiled and dried meat is considered a delicacy 

 and is called beche-de-mer or Irepang. 



CLASS ECHINOIDEA (Sea and Heart Urchins, 

 Sand Dollars) 



Diagnosis: body globular (sea urchins), heart- 

 shaped (heart urchins), or disc-like (sand dollars), 

 covered by movable spines; no tentacles around 

 mouth; arms absent (Figure 15.3). 



The sea urchins, heart urchins, and sand dollars 

 (sometimes called cake urchins) like all echinoderms 

 are marine animals. Sea urchins are most often seen 

 along rocky shores, where they live in holes in rocks. 

 Others occur on the ocean floor in bays or other shal- 

 low coastal waters. Sometimes they can be found in 

 the holdfasts of kelps that have been washed ashore. 

 Heart urchins are inhabitants of muddy bottoms, and 

 sand dollars of the sand of bays and shallow coastal 

 waters. The echinoids have a variable diet of sea- 

 weeds, dead animal remains, small organisms, and 

 organic matter contained in ingested sand or mud. 



Characteristically, the sexes are separate and the 

 eggs and sperms are spawned simultaneously. In 



Figure 15.3 Echinoid types: obove, Dendrasler, a sand dollor (a 

 moderately small specimen); thicker, but similar, species often are called 

 sea biscuits; those species with holes near the margin are called keyhole 

 sond dollars, and similar species with marginal notches ore called 

 notched sand dollars; center, tovenio, a heart urchin (x 1); bottom, 

 Strongy/ocentrotus, a sea urchin (small specimen); other sea urchins vary 

 in body size and In spine number and spine proportions. 



