dollar and sea cucumber burrowing provides more oxygen at greater depths of the sea floor,
thus allowing a more complex ecological community to develop. In addition, starfish and
brittle stars prevent the growth of algal mats on coral reefs, so that the coral can more
effectively filter-feed.
Echinoderms are also the staple diet of many organisms, including the otter. Many sea
cucumbers provide a habitat for parasites, including crabs, worms, and snails. The extinc-
tion of large quantities of echinoderms appears to have caused a subsequent overrunning of
ecosystems by seaweed, causing the destruction of entire reefs.
Economically, in some countries echinoderms are regarded as delicacies. Around 50,000 tons
of sea urchins are captured each year, and certain parts are consumed mostly in Japan, Peru,
and France. Sea cucumbers are considered a delicacy in some southeastern Asian countries.
Some sea cucumber toxins slow down the growth rate of tumor cells, so there is an interest
in using these in cancer research. The calcareous external covering of echinoderms is used
as a source of lime by farmers in some areas where limestone is unavailable and 4,000 tons
of the animals are used each year for this purpose.
Lesson Summary
- Echinoderms belong to the phylum Echinodermata, the largest phylum without fresh-
water or terrestrial members. - Echinoderms are radially symmetric, they have an endoskeleton, some have calcareous
spines they have a unique water vascular system, a simple digestive system, an open
and reduced circulatory system and a modified nerve net. - Fertilization is generally external; regeneration is fairly common among echinoderms;
feeding strategies vary greatly. - Echinoderms consist of two main subdivisions, the motile Eleutherozoa and the sessile
Pelmatazoa. - Echinoderms are distributed all over the world at almost all depths, latitudes, and
marine environments. - Echinoderms play an important role in the ecological community. Economically, they
are eaten as delicacies in different countries, they play a role in cancer research, and
they are used as a source of lime.
Review Questions
- What are the characteristic features of echinoderms?
- What feeding strategies are represented in the echinoderms?
- What protection do echinoderms have against predation?
- Chemical elements within the skeleton makes it stronger and more resistant. How
could this be an advantage in grazing echinoderms?