Echinoderms

Phylum echinodermata

Exclusively marine

appeared in camp rain period (540MYA)

7000 living spp.

5 extant classes

pentaradial symmetry

Echinoderm characteristics

endoskeleton covered by epidermis

cancerous plates (ossicles) secreted by the dermis

bilateral larvae

no obvious segmentation

no CNS
regeneration of tissues, organs and limbs

Asexual reproduction

5 echinoderm classes

Asteroidea - starfishes

Crinoidea - sea lillies

Echinoidea - sea urchins

Holuthuria - Sea cucumbers

Ophiuroidea - brittle stars

Asteroidea

1500 species

5 or more arms radiate form central disc

opportunistic feeders - predators of benthic invertebrates

reproduce sexually or asexually

Water vascular system

water filled canals

muscular tube feet extended by hydraulic pressure

Ampulla - rounded sac that acts like a squeeze bulb

tube feet used for locomotion, feeding and gas exchange

Ossicles with tube feet

ambulacral plates

Gills

Papulae on upper surface

Pedicellariae

Jaw-like appendages - asteroids and echinoids

defence and cleaning

Asteroid feeding types

Short armed species - swallow entire prey

Long armed species - evert stomach - partial digestion outside body

bivalve feeders - fatigue bivalve adductor muscles - slide stomach between valves

Asteroid reproduction

gonochoristic - eggs and sperm shed into the water column

one breeding season a year

single female lays 60000000 eggs per year

Asteroid larvae

Bipinnaria and plates with ciliated bands

Percentage of disk attached for regeneration

20%

Paine (1966) concept of keystone species star fish

Pisaster ochraceus

crown of thorns star fish

Acanthaster planci

21 arms

can consume 6m2 of reef per year

How does crown of thorns starfish feed on coral

extrudes stomach onto polyps

Ophiuroidea

1500 species

body with 5 slender arms

2 clades of Ophiuroidea

Ophiurida — brittel stars

Euryalida — basket stars (deep water)

Echinoidea

100 species

Spines

Tube feet for locomotion

feed on algae

Aristotle’s lantern

jaw on oral surface - 5 rigid teeth

Irregular echinoids

Sand dollars - Clypeasteroidea (dorsoventrally flattened)

Heart urchins - Spatangoida

Crinoidea

sea Lillies or feather stars

600 species

Suspension feeders

Holothuroidea

Sea cucumbers

tough outer skin

sub-dermal endoskeleton

scavengers