Phylum Echinodermata
GENERAL CHARACTERS
HABIT AND HABITAT
The Echinodermates
are exclusively marine including the largest invertebrate “Giant Squids.”
EXTERNAL FEATURES
§ Symmetry usually radial, nearly always pentamerous.
§ Body shape is rounded to cylindrical or star like.
§ Surface of the body is rough.
§ Body wall consists of an outer epidermis, a middle dermis and
inner lining of peritoneum.
INTERNAL FEATURES
§ Endoskeleton consists of closely fitted plates forming shell
usually called “THECA,” may be composed of separate small “OSSICLES.”
§ Coelom is spacious, lined by peritoneum and occupied mainly by
digestive and reproductive systems.
§ Presence of “Water Vascular System” is most characteristic
feature.
§ Alimentary tract is usually coiled.
§ Circulatory or Haemal or blood lacunar system is typically
present.
§ Excretory system is wanting.
§ Nervous system is primitive, consists of ganglionated nerve
cord.
§ Sense organs are poorly developed.
§ Sexes are usually separate.
§ Reproduction is usually sexual, fertilization is external.
WATER CANAL SYSTEM
Water canal system
is unique in possessing an internal closed system of canals containing a watery
fluid.
REGENERATION
Regeneration of
lost part is common
IMPORTANCE OF WATER CANAL SYSTEM
These canals are
provided with tubular protrusions called “Tube Feet,” which serve a number of
functions like locomotion, anchoring to hard surfaces, grabbing the prey,
diverting food particles towards mouth and in some cases also respiration. The watery
fluid is drawn from the surrounding water through a perforated disc called the
“Madreporite.”
EXAMPLE
Star Fish, Brittle
stars, Sea urchins, Sea-cucumbers, Sea-Dollar, Sea-lilies and Feather stars.
LARVA
Bipinnaria larva
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