ECHINODERMAT
A
Instructor: Almonther I. Alhamedi
The Islamic University of Gaza
Department of Biology
E-mail : mhamedi@iugaza.edu.ps
Web page :http://site.iugaza.edu.ps/mhamedi
CHARACTERISTICS OF PHYLUM ECHINODERMATA
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1.
Body
unsegmented
(nonmetameric)
with
radial,
pentamerous symmetry; body rounded, cylindrical, or star
shaped, with five or more radiating areas, or ambulacra,
alternating with interambulacral areas
2. No head or brain; few specialized sensory organs; sensory
system of tactile and chemoreceptors, podia, terminal tentacles,
photoreceptors, and statocysts.
3. Nervous system with circum oral ring and radial nerves;
usually two or three systems of networks located at different
levels in the body, varying in degree of development according to
group.
4. Endoskeleton of dermal calcareous ossicles with spines or
of calcareous spicules in dermis; covered by an epidermis
(ciliated in most); pedicellariae (‫)المالقط‬.
CHARACTERISTICS OF PHYLUM ECHINODERMATA
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5. A unique water-vascular system of coelomic origin
that extends from the body surface as a series of tentaclelike projections (podia, or tube feet) that are protracted
by increase of fluid pressure within them; an opening to the
exterior (madre-porite (‫) المصفاة‬or hydropore) usually present.
6. Locomotion by tube feet, which project from the
ambulacral areas.
8. Excretory organs absent
9. Sexes separate (except a few hermaphroditic).
10. Autonomy and regeneration of lost parts conspicuous
CLASS ASTEROIDEA
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Sea stars, often called starfishes, demonstrate the basic
features of echinoderm structure and function very well,
and they are easily obtainable.
Sea stars are familiar along the shoreline where large
numbers may aggregate on rocks.
They are often brightly colored and range in size from a
centimeter in greatest diameter to about a meter across.
Cross section of arm at level of gonads, illustrating open
ambulacral grooves.
CLASS OPHIUROIDEA
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Brittle stars are largest of the major groups of
echinoderms in numbers of species, and they are
probably the most abundant also.
snake
Brittle star Ophiura lutkeni (class
Ophiuroidea). Brittle stars do not
use their tube feet for locomotion
but can move rapidly (for an
echinoderm) by means of their
arms.
CLASS ECHINOIDEA
Echinoids have a compact body enclosed in an
endoskeletal test, or shell. Dermal ossicles, which
have become closely fitting plates, make up the
test.
 Echinoids lack arms.
 The majority of living species of sea urchins are
“regular”; they have a hemispherical shape,
radial symmetry, and medium to long spines.
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Two sand dollar species. A, Encope grandis as normally found
burrowing near the surface on a sandy bottom.
CLASS HOLOTHUROIDEA
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sea cucumbers
Anatomy of the sea cucumber Sclerodactyla. A, Internal. B, External.
Red, hemal system.