Phylum Echinodermata

20.6.8

ECHINODERMATA

q Non-segmented animals. Adult with radial symmetry characterized by five or more radiating area. The larvea echinoderms were bilaterally symmetrical.

q The animals show no cephalization and no head or brain.

q  They are at the organ system level of organisation.

q The echinoderms are enterocoelomic, triploblastic deuterostomes

q There is no anterior or posterior, right or left, dorsal or ventral. Instead there is an oral surface and an aboral surface.

q They have a complete digestive system.

q They have an endoskeleton of dermal calcareous ossicles covered by an epidermis.

q The echinoderms possess a water vascular system and tube feet. The tube feet are the major locomotory system for most echinoderms.

§  The coelom is extensive, involving the water

vascular system and a large perivisceral cavity.

§  The circulatory and excretory systems are reduced or absent.

§   Respiration is via the general body surface or special gills, tube feet, papulae, and etc.

§  The nervous system consists of a nerve ring and 5 radial nerve cords.

§   Locomotion is by tube feet, spines or arm movement.

 Sexes are separate, fertilisation external and development involves a free-swimming, bilaterally symmetrical larva

Classification of Echinodermata

•        Five classes:

                              i.            Class Asteriodea ( Asterias)

                           ii.            Class Holothuroidea ( Holothuria )

                        iii.            Class Crinoidea ( Sea lily)

                         iv.            Class Echinoidea ( Sea urchin )

                            v.            Class Ophiuroidea ( Ophi

ECHINODERMATA

v     ASTEROIDEA

v     HOLOTHUROIDEA

v     CRINOIDEA

v     ECHINOIDIA

v     OPHIUNOIDEA

ASTEROIDEA

CHARACTERISTICS :

·    STAR SHAPED WITH ARMS,NOT SHARPEDLY MARKED OFF

·    AMBULACRAL GROOVE OPEN,TUBE FEET ON ORAL SIDE

·    TUBE FEET OFTEN WITH SUCKERS

·    EXAMPLE : SEA STARS

HOLOTHURIDAE

CHARACTERISTICS :

·    CUCUMBER SHAPE WITH NO ARMS

·    SPINE ABSENT

·    AMBULACRAL GROOVES CLOSED

·    TUBE FEET WITH SUCKERS

·    EXAMPLE : SEA CUMBER

CRINOIDEA

CHARACTERISTICS :

·    FIVE ARMS BRANCHING AT THE BASE AND BEARING PINNULES

·    CILIATED WITH AMBULACRAL GROOVES ON ORAL SURFACE WITH TENTACLES LIKE TUBE FEET

·    EXAMPLE : SEA LILIES

ECHINODIA

CHARACTERISTICS :

·    MORE OR LESS GLOBULAR OR DISC SHAPED WITH NO ARMS

·    MOVABLE SPIRES

·    AMBULACRAL GROOVE IS CLOSED

·    TUBE FEET WITH SUCKERS

·    EXAMPLE : SEA URCHINS,PURPURATUS

OPHIUNOIDEA

CHARACTERISTICS :

ü     STAR SHAPED WITH ARMS SHAPED MARKED OFFCENTRAL DISC

ü     AMBULACRAL GROOVE IS CLOSEDTUBE FEET WITH SUCKERS AND NOT FOR LOCMOTION

•        Most echinoderms have calcite skeleton.  such as ophioroids (brittle stars).

•        The coelom of Echinodermata importance not only in carrying and distributing nutrients, respiratory gases, excretory and storage products but also in functioning as a water‑vascular system.

•        Skeleton in form of rods supporting arms and other projections; such as:

•        Asteroids get from the starfish and echinoids can get from sea urchins.

•        It forms more‑or‑less rigid capsule.

•        isolated spicules in the integument.

•        Star fish can threaten the coral reef.

•        Holothuria function in the medical field.

•          Holothuroids can be found in sea cucumbers.