Echinoderms
Class Echinoidea
Key words
echinoderm
echinodermata
Echinoderms
(Phylum Echinodermata)
Echinoderms are a group of
exclusively marine animals. It is the
largest phylum with no freshwater or
terrestrial representatives.
● There are about 70,000 living
species.
● They range in size from less than an
inch (20 mm) to the tiger’s tail sea
cucumber at 6 feet (2 m) long.
● The name echinoderm, meaning
“spiny-skinned,” derives from the
spines embedded in the body
wall of most forms.
● Most echinoderms have
radial symmetry, with components
distributed to a five-part plan.
● Many echinoderms are able to regrow
large parts of their bodies. A starfish
cut radially into several parts (like
cutting a cake) can eventually
regenerate into the same number of
individual starfish.
● The water vascular system, a hydraulic
system used to extend and withdraw
tubed feet or tentacles, is unique to
echinoderms.
● There are six classes, five of which
have common marine representatives:
class Echinoidea (sea urchins,
sand dollars);
class Asteroidea (sea stars
or starfish);
class Opiuroidea (brittle stars);
class Crinoidea (feather stars,
sea lilies);
class Holothuroidea (sea
cucumbers);
class Concentricycloidea (sea
daisies)—only two species are
known.
Class Asteroidea
sea urchin
sea star
(starfish)
Class Opiuroidea
brittle star
Class Crinoidea
Class Holothuroidea
sea cucumber
sea lily
(feather star)
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