A Sea Star

A Sea Star Eating

Sea stars are the largest population of Echinoderms. Sea stars have a huge appetite and use their arms to open the shells of bivalves, mainly clams and oysters. Sea stars have an open groove down each arm, full of tube feet that end in suckers for holding onto food and distinguishing light from dark. Once a bivalve's shell is open, sea stars project their stomach between the shells in order to eat inside. In addition to eating bivalves, a large population of sea stars can destroy a coral reef.

Why is a big population of sea stars bad for a coral reef?

Because a big population of sea stars can eat many of the corals, destroying the reef.

Members of class Crinoidea, such as the sea lily shown above, can move with with their feathery-looking arms, but normally they are attached to a surface. They use their tube feet, which cover the ventricle side (bottom) of their arms to filter feed.

If adult sea lilies are attached to a surface, how do they eat?

Adult sea lilies use the tube feet on their feathery arms to filter feed.

Sea Urchin

Sand Dollar

Members of class Echinoidea are covered in spikes and tube feet and lacks arms. Spikes are used for both movement and defense against predators. Tube feet are used to climb, attach to surfaces, and capture food. Sea urchins eat algae. Sand dollars burrow in the sand and eat detritus, or dead matter.

Why are both sea urchins and sand dollars classified as Echinoideas?

Because both sea urchins and sand dollars are covered in spikes and tube feet.

A Sea Cucumber

Sea Cucumber Anatomy

Sea cucumbers, as shown above, use their tentacles to capture food. They can also filter feed, using tube feet. Sea cucumbers have a high economical value in both pharmaceutical and food industries. Sea cucumbers secrete a substance from their skin that kills bacteria and also reduces inflammation (red, hot swollen part of the body due to an infection). The body wall muscles of sea cucumbers are called trepang, which is a multimillion-dollar gourmet food.

What two industries value sea cucumbers?

The pharmaceutical and food industries value sea cucumbers.

Basket Star

Brittle Star

Members of class Ophiuroidea, such as brittle star and basket star, use their arms to move fast, capture food, and collect sensory information, especially light detection. These are the only Echinoderms that have tube feet that lack suckers to hold onto food. Instead, brittle stars wrap their snake-like arms around food and take the food to their mouth. If a predator attacks, a brittle star's arm will break off easily, hence the name "brittle." Basket stars extend their arms to capture food floating in the water. Once food is captured, the basket star directs the food into its mouth.