Echinoderm
means spiny skin. Echinoderms include sea urchins, sea stars, sand
dollars, sea cucumbers and some other odd organisms like feather stars
and basket stars. All echinoderms have radial symmetry, spiny skin, and
an endoskeleton called a test.
Most people are familiar with an orange sea star because on the east
coast, that's all we've got. On the west coast and in other places
around the world, it is easier to find a variety of
sea stars in other colors and with different amounts of legs.
Sea stars have powerful tube feet that use water suction to open
molluscs. When they eat molluscs, they actually stick their stomach into
the shells of the mollusc, digest it, and then put their stomach.
Feather stars and basket stars both have crazy looking legs that they
wave around to filter feed. Sea urchins and sand dollars are both
covered with protective spines and eat with a scraping mouth called
Aristotle's Lantern.
Sea cucumbers have lost most of their exoskeleton and are a bit
squishier than other echinoderms. Sea cucumbers are important detritus
eaters on the sea floor. When attacked by predators they will expel
their guts as a meal for the predator as they make a get away. Sea
cucumbers are able to regenerate these guts over time.