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Phylum Echinoderm
Echinoderm
• Mostly sessil life
• Adult has no head or brain
• Central nervous system with nerves
radiating into arms
• All marine
• Echinodermata – spiny skinned
Cont…
• Most adults have pentaradial symmetry
(all radial)
• Larvae have bilateral symmetry
• Separate sexes ; some hermaphrodites do
exist
• Sea stars (not star fish); brittle stars; sea
cucumbers; sea urchins, sand dollars, etc.
• ~ 8,000 to 10,000 species
Characteristics
1. Endoskeleton an internal skeleton of
calcium carbonate of tiny plates called
ossicles- can be fused together
2. Pentaradial (Five part radially
symmetrical most have five arms)
Characteristics Cont…
3. Water vascular system water
system of connective canals
and tube feet that are used for:
locomotion, gas exchange,
sensory, and capture food
– Tube feet – muscular extension of
water filled canals
• End is a sucker (attachment /
locomotion)
Cont…
4. Coelomic circulation and respiration
body cavity functions as a simple
circulatory system where particles move
through the fluid– Have skin gills projections that are between
the spines
Regeneration
• Many species autotomize,
leaving predators with a
nutritious souvenir while
they escape
• Most sp. can regenerate
from fragments
Sea Stars
• Most have 5 arms
– Some have more (even 50)
• Carnivores (Bivalves ; snails ; barnacles ; etc.)
– Ejects stomach inside out through mouth into
the prey
– Digestive enzymes are secreted and the
digested food is carried into the glands for
absorption
– Stomach is then pulled back inside body
Feather Stars and Sea lilies
• Mouth is located on the upper surface
• Sessile but can detach & move around
• Attached to sea floor with a stalk
• Mouth & anus on upper surface
Brittle Stars
• Slender branched arms that readily break
off & regenerate
• Move quicker than sea star
• Feed by raking in food with arms or
trapping it with its tube feet
Sea urchins and Sand dollars
• Have the five distinct body parts
• Body shaped like a sphere (sea urchin) or
a flattened disk (sand dollar)
• Lack arms
• Bodies covered with movable spines
Sea Cucumbers
• Softer
• Lack arms
• Live on ocean bottoms hiding
in caves during the day
• Show bilateral symmetry
• Can eject parts of their
internal organs (evisceration)
to scare predators; regenerate
these structures in days
HW
1. List the major echinoderm characteristics
2. Explain why some echinoderms would
have bodies that are softer than others
3. Compare and contrast two examples of
echinoderms.
• http://sps.k12.ar.us/massengale/echinoder
m_notes.htm
• http://www.wphs.ocps.net/tl/rouppj/roup
pj_files/EchinodermsPPTJR_files/frame.ht
m