MFWB_A - Echinoderm form, function and locomotion

classes

Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, Crinoidea

common features

marine, intertidal to deep, mainly benthic, no head region or brain. calcirous endoskeleton, deutreostomes, coleomate, calcerous plates (ossicles, bound by catch collagen), radial pentamerous symmetry

coelomic systems

perivisceral cavity, haemal system, peri-haemal system, water vascular system

perivisceral cavity

guts and gonads, organs

haemal system

nutrient distribution

peri-haemal system

nutrient distribution

asteroidea

1500, starfish, sea stars, sea daisies, intertidal/coral reefs, central disc with usually 5 arms, up to 40, 12-25 cm diameter, mouth on benthos, pentamouros symmetry, ambulacral groove in middle of arms surrounded by tube feet (podia), sensory tentacles and eyespots at end of arms, spines and pedicellariae on aboral

pedicellariae

jaw-like appendages for cleaning and defence

respiration in asteroidea

projections of coelomic cavity (papulae) - specialised gills that bring oxygen to the peri-visceral coelom, podia act as gills for oxygen transfer to water vascular system, which is open to environment via madreporite

ophiuroidea

over 2000, brittle, 10-15cm, benthic, 3000-6000m, usually 5 slender arms distinctly offset from central disc, no ambulacral grooves, papulae or pedicellariae, podia not primarily for locomotion, arms can propel, articulated ossicles (like vertebrae) in arms aid flexibility

Ophiuroidea respiration

5 pairs of in-foldings (bursae) act as gills, cilia inside brings oxygenated water in, water vascular system similar to asteroids, maderoporite on oral surface

Echinoidea

950, urchins, biscuits, sand dollars, benthic, rocks substrate rather than sandy, ossicles fused to form skeletal test, spines connected by ball and socket joint, moved by muscles, pedicellariae distributed across test

regular urchins

sea urchins, radially symmetrical, hemispherical in shape with long spines, tubed feet used for locomotion

irregular urchins

heart urchins and sand dollars, bilaterally symmetrical, flatter with short spines, used for locomotion

pentamorous symmetry

5 ambulacral areas (tube feet) and 5 interambulacral areas

Echinoidea respiration

WVS similar to Asteroidea, peristomal gills around mouth bring oxygen to muscles/organs, blood pumped into gills, oxygen diffuses in and around, tubed feet also acts respiratory organs, oxygen to WVS

Holothuroidea

1200, most over 10cm, sea cucumbers, elongated from oral to aboral axis, bilaterally symmetrical, locomotion with tubed feet and muscular contraction, lack endoskeleton, ossicles greatly reduced generally, no spines or pedicellariae

gas exchange in holothuroidea

WVS similar to others, buccal podia (modified tube feet), tube feet, respiratory tree in cloaca, evisceration (defence or detoxification), organs of Cuvier (sticky mass of tubules, can have toxins)

crinoidea

100 sea lilies, 600 feather stars, lilies - anchored to substrate by stalk, feather - root-like cirri grasp substrate, up to 6000m, sessile (lilies), sedentary (feather) mouth orientated upwards, central disc/calyx, 5-10 arms, arms subdivided into more arms with jointed pinnules, tube feet between for feeding, radial pentamerous symmetry, alternating movement of arms allow short distance swimming

Crinoidea gas exchange

WVS, no madreporite, tube feet main site for gas exchange

structure and function of spines

protection and defence, made from rod shaped ossicles, primary (large) and secondary (small) spines, starfish/brittle stars have simple spines, urchins have complex with nerve ring, circular muscle and catch collagen, some are hollow and have toxins - saponins

catch collagen

mutable collagenous, tissue of echinoderms, changes its mechanical properties in response to stimulation

structure and function of pedicellariae

asteroids and echinoids, 4 main types - tridactyl, ophiocephalous, trifoliate, gemmiform

locomotion

crinoids - sedentary, some can crawl/swim, ophiuroids - crawl using arms, holothuroids - some burrow, some creep using tube feet on sole, echinoids - tube feet (regular) and spines (irregular)

WVS

water enters via maderoporite then stone canal, from there to ring canal then radial canal, lateral canal connects to ampullae and tube feet, WVS is lined with cilia and muscle

steps for WVS contraction

contraction of postural muscle, contraction of ampulla muscles - move water to extend foot, contraction of retractor muscles on opposite side of foot, contraction of foot muscles to expel water back into ampulla