Echinodermata Flashcards
what are the key characteristics of deuterostomes?
radial cleavage
secondary mouth - not formed by anus
three part enterocoelic coelom
dipleurula-type larvae
basic features of echinoderms?
trimeric coelom deuterostome development biradial symmetry in larva pentaradial symmetry in adults calcareous endoskeleton water vascular system
describe the skin of echinoderms?
endoskeleton
ciliated epidermis forms thin mucoid skin
spines
papulae
pedicellaria
ossicles - calcium carbonate crystal hollowed into a lattice, laced together with collagen
what are spines used for?
digging, walking, paddle, defence
what are pedicellariae?
jaws often with toxins
used for defence, cleaning, and food capture
characteristics of tube feet?
project downwards from main radial pipe
ampullae connected laterally to main piping
ambulscral grooves run along underside of each arm
what are tube feet used for?
locomotion, respiration, feeding, sensitivity
what is the water system?
closed hydrostatic - uses pipes - a central ring plus a pipe up each arm and a single connection to outside world via madreporite
reproduction in echinoderms?
mass spawning or asexual regeneration
key absences in echinoderms?
no real CNS - simle 5 -rayed nerve net at base of epithelium
no distinct excretory system
weird connective tissue - contractile and changes mechanical properties in response to nerve stimulation - energy catch/saving
key features of asteroidae?
starfish/sea stars
usually 5 arms (can be other odd numbers)
mainly sitting substratum in inshore waters
arms have ventral ampullae and large coelom containing parts of gut/gonads
respire by thin papulae
how do asteroidae move?
stepping action of coordinated tube feet, with ampullae providing the extrusion force
more complex nerve plexus than in other classes which is used to provide stepping coordination
no one leg leads consistently
how do asteroidae feed?
tube feet provide suction over long period of time until mussel finally opens slightly and stomach of starfish exterted and pushed into gap where it extrudes enzymes that turn the mussel into gloop
why do starfish matter?
depeltion of mussel beds in temperate areas
crown-of-thorns sea star is a major problem, grazing coral reefs
key characteristics of ophiuroidea?
brittle stars/basket stars
central disc with five thin arms - sometimes subdivided to make a basket-like arrangement
how do ophiuroids feed?
they're scavengers abundant on ocean floor as 'hoovers' arms move decaying matter into mouth few carnivores lack anus
how do ophiuroids move?
use each arm as a limb/lever
ossicles large and articulated so act like vertebrae
how do ophiuroids breathe?
via 5 bursae projecting into the coelom from ventral disc, between the arms
key features of echinoidea?
no arms but still pentandrical with five rows of tube feet
ossicles fused to make a complete test
some irregular - show pentamery but also bilateral
how do echinoidea move?
stout surface spines will ball and socket joints
spines can act as legs
some role for ventral tube feet which have ampulla
how do echinoidea eat?
graze on coral/algae using ventral aristotles lantern - a complex array of five articulated teeth and muscles
how do echinoidea breathe?
occurs all over general body surface
general features of holothuroidea?
appear bilateral - cylindrical
5 rows of tube feet and terminal tentacles
no spines, ossicles small and separate - soft
how do holothuroidea move?
using 2-3 ventral rows of tube feet and sometimes worm-like hydrostatic burrowing
how do holothuroidea eat?
using tentacles to sweep over substratum and pick up food
how do holothuroidea breathe?
by internal branching - lung like in structure - at rear of body from cloaca
general features of crinoidea?
most ancient class - pre-Cambrian - mostly extinct
mouth points upwards
may be up to 200 arms supported by internal ossicles
most stalked and attached to substratum
how do crinoidea move?
if stalked they don’t
free-floating ones flap arms or ‘snowshoe’ along substratum w/ basal arms
how do crinoidea eat?
filtering - pinnules on arms flick food to midline, where tiny ciliated tube feet make a fine filter and transfer particles to food groove leading to mouth
what is concentricycloidea?
sea dasies - new-ish class flattened disc, armless, lives in rotting wood like piers
why are echinoderms weird?
adults pentamerous while larvae bilateral
weird skeleton - no nervous system - head/anterior
catch system - stiff to fluid
any arm can lead
large size but no real closed blood system
never pelagic or parasitic
what is the traditional view regarding phylogeny?
became radial as became more sessile
crinoids basal, then echinoideas and holothurideas and then sea stars and brittle stars
what is the view based on development?
deuterostomes
crinoids - most primitive
e/h - sister groups
asteroids/ophiuroids - closely related
