Download phylum echinodermata

PHYLUM ECHINODERMATA
Aquatic Science – Mrs. Walker
I. General
A. Ex.: starfish, urchins, sea cucumbers
B. Echinoderm means “spiny skin” (referring to bony ossicles
(CaCO3) beneath skin)
C. radial symmetry
D. all are benthic
E. complete digestive tract
F. no head or brain
G. have sense of touch, chemosensitivity, and can detect light
with sensitive eye spots (ends of tentacles): light energy is
converted into electrical impulses which are carried by nerves to a
central nerve ring around the mouth, which coordinates movement
of the arms through radial nerves
H. separate sexes
I. meroplankton larvae
J. external fertilization
K. Water Vascular System: (only phylum to have this)
1. circulates water through a system of canals
2. used in feeding, respiration, excretion and movement
3. madreporite or sieve plate: external opening to the
system
a. water enters here and passes to the ring canal
b. branches from ring canal to the ray (radial) canals and
tube feet
4. tube feet (locomotion)
a. water is pulled into the ampullae and it contracts (like
bulb on an eyedropper) and forces water into tube feet, which
extend
b. the tube feet suck onto a surface as water is pushed
out by tube feet muscles
c. water is pushed back in and the tube feet release
II. Five Classes
1. Class Asteroidea (starfish)
a. bony ossicles made of CaCO3 connect to a internal
skeleton and provide
flexible support (endoskeleton)
b. most have five rays attached to a central disk
c. have obvious tube feet used to move over the rocky
benthic habitat
d. carnivores: feed on polyps, mollusks, etc (8-15
oysters per day).
1. pull on bivalve adductor muscles until they relax
and shell opens
2. lower their stomachs into the bivalve and begins
external digestion
e. regeneration possible when part of center disk is
attached to removed ray
f. breathe through tube feet and dorsal skin gills
g. small digestive system because don’t have a lot of
undigested food (liquefy)
2. Class Echinoidea (sea urchins and sand dollars)
a. ossicles fused into spherical tests (internal skeletons
formed from bony plates fused together
b. spines protrude from test
sea urchin
1. live in rocky or coral substrates
2. spiny urchins have pointed toxin-tipped spines used for
protection
3. spines and tube feet are used for movement
4. graze on algae, hydroids, etc.
5. have a 5-part mouth structure called Aristotle’s Lantern
6. can chip holes in rocks to hide in
7. have endangered kelp (eat holdfasts and stipe).
sand dollars
1. reduced tube feet but use short spines for movement
2. found in the sublittoral zone of sandy shorelines
3. lie tilted on side and feed on organisms found between the
sand grains, gathered on strings of sticky mucus (diatoms and
organic debris)
4. 5 part mouth: when removed from the sand dollar they tend to
fall apart and look like little birds or doves (rattle sound inside)
3. Class Ophiuroidea (brittle stars)
a. largest echinoderm class
b. resemble starfish but arms are attached separately to the
central disk
c. arms break off easily but will regenerate
d. found in shallow to deep ocean floor
e. solitary, nocturnal, avoid light and are usually found in
crevices or on open sea floor at the darker depths
f. reduced tube feet: move mainly with muscular, spiny arms
g. primarily detritus feeders (scavengers): lie on back and catch
food with sticky strands on arms
4. Class Holothuroidea (sea cucumbers)
a. soft, elongated bodies with tentacles on one end
b. lie on side and filter or deposit feed with tentacles (modified
tube feet)
c. have five rows of tube feet but look very little like other
echinoderms
d. may eviscerate to startle predators or entangle prey in
sticky, toxic strands (intestines quickly regenerate)
e. water taken in by anus and passed over a respiratory “tree”
where body fluids absorb O2
f. open anus allows for small organisms to enter and take up
residence so some have teeth around anus to prevent invaders
g. delicacy in some Asian countries ($80.00)
5. Class Crinoidea (feather stars and sea lilies)
a. small, primitive class: was much larger in past
b. most live in deep water
c. sessile: most are attached with a stalk
d. most are 15 – 30 cm tall
e. feathery arms filter feed