Figure 12.14: This passion flower feather star is an echinoderm. ( 36 )ThefollowingtablesummarizesthefourmainclassesofechinodermspresentintheEleuthero-
zoa Group:
Table 12.2:Echinoderm Class Representative Organisms
Asteroidea Starfish and sea daisies
Ophiuroidea Brittle stars (Figure12.15)
Echinoidea Sea urchins and sand dollars
Holothuroidea Sea cucumbersFigure 12.15: The giant red brittle star, an ophiuroid echinoderm. ( 28 )Echinoderms are distributed all over the world at almost all depths, latitudes, and environ-
ments in the ocean. They are in highest diversity in reefs but are also widespread on shallow
shores, around the poles (where crinoids are at their most abundant) and throughout the
deep ocean, where bottom dwelling and burrowing sea cucumbers are common, sometimes
accounting for up to 90% of organisms.
While almost all echinoderms are benthic (live on the sea floor) some sea-lilies can swim at
great speeds for brief periods of time, and a few deep-sea sea cucumbers are fully floating.
Some crinoids attach themselves to floating logs and debris and some sea cucumbers employ
a similar strategy, attaching to the sides of fish.
Roles of Echinoderms
Echinoderms play roles both ecologically and economically. Ecologically, sea urchin grazing
reduces the colonizing of bare rock by such organisms as mussels and barnacles, and sand