ECHINODERMS explanation .......ppt BEST OF LUCK

1. Phylum
Echinodermata
Lecture-10

2. General Characteristics
• Radial symmetry
• Several arms (5 or more, mostly grouped 2 left- 1 middle- 2 right) radiating from a central
body.
• Body consist of equal segments, each containing a duplicate of various internal organs.
• No brain nor hearts
• With eyespots on each arm
• Mouth situated on the underside and anus on top (except feather stars, sea cucumbers and
some urchins).
• Contains tube feet with suction pads controlled by water vascular system.
• Some are carnivorous while others are detritus foragers.
• Reproduction is through release of sperms and egg into the water.
• Capable of regeneration and fragmentation.

3. Classes of Echinoderms
• Class Asteroidea
• Class Ophiurodea
• Class Echinoidea
• Class Holothuroidea
• Class Crinoidea

4. Class Asteroidea
• Carnivorous and feed on sponges and molluscs some are specialized feeders.(crown of thorns)
• Doesn’t have hard mouth parts to help them capture prey.
Crown of thorns (Acanthaster planci)
• One of the largest and the most venomous starfish.
• Size reaches up to 50 cm in diameter.
• 10 to 20 spiny arms with formidable thorn like toxic spines
• Feed on coral polyps
• Predators: Triton shell and some puffer fish
Crown of Thorn

5. Class Ophiurodea
• Close relatives of sea stars
• Have five snakelike arms which are highly flexible.
• No replication of internal organs, just one set in the central disk.
• Smaller central disk and no anus.
• Arms of brittle stars are fragile. ( Defense Mechanism)
• Most active and fastest moving echinoderms
• Feed on plankton but also on detritus.
Examples
• Serpent Stars; Coiled around branches of gorgonians.
• Basket stars ;Specialized type of brittle stars
Serpent star
Basket star

6. Class Echinoidea
• External chitinous skeleton and a centrally located jaw
• Some have speherical bulblike cloaca.
• Movable spines are attached to the body, some are venomous
• Locomotion by tube feet but also by movement of the spines on the underside of the body.
• Generally nocturnal
• Most are algal grazers but some feed on sponges and detritus.
Sea Urchins

7. Class Holothuroidea
• Do not have radial symmetry but are bilateral.
• Cucumber shaped with elongated muscular, flexible body with mouth at one end anus on the
other.
• Tentacles present in the mouth for food collection
• Feed on rich organic film coating sandy surfaces.
• Crawl over the bottom and ingest sand.
• Move by means of tube feet.
• Releases its digestive tract when threatened (defense mechanism)

8. Class Crinoidea
• Radial symmetry
• Cup-shaped body
• Numerous feathery arms project from a central disc.
• Have 5 up to 200 arms (pinnules)
• Nocturnal
• Usually cling to sponges.
Feather stars