Download Phylum Echinodermata

Echinodermata
y Spiny skinned animals with radial symmetrical body
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plan.
Rays emanating from a common center.
Internal skeleton of hardened plates of calcium
carbonate.
Water vascular system and tube feet – locomotion,
feeding, respiration, internal transport, and waste
removal
Close to chordates because of the development of a
bilateral larval stage that is similar to that in
chordates and the presence of an internal skeleton.
Vascular System:
y Madreporite – Calcareous sieve like opening to the
outside that is used to filter into the water vascular
system.
y Ring canal – at the center of the seastar from which
the filtered water from the madreportie is distributed
to the radial canal
y Radial canal – carry water to the ampulla (reservoir
portion) of the tube feet.
y Tube feet – off radial canal
Feeding:
y Carnivorous – Sea stars pry open clam shells with
tube feet and extend their stomachs and digestive
juice right onto shell.
y Herbivors – Sea urchins scrape off algae, some sea
stars.
y Filter feeders – sea lilies, feather stars.
y Detritus feeders – sea cucumbers, some sea stars.
Respiration:
y Some have skin gills
y Thin walled tube feet
Internal Transport:
y Nutrients move in fluid within body cavity and
digestive glands
Excretion:
y Solid Æ anus – except in brittle stars
y Nitrogenous waste – gills and tube feet
Response:
y Primitive nervous system.
y Nerve ring and radial nerve.
y Some have statocysts (A small organ of balance in
many invertebrates, consisting of a fluid-filled sac
containing statoliths that stimulate sensory cell).
Response Con’t
y Chemoreceptors for finding food.
y Sea stars – have photoreceptors (light/dark).
y Few protective responses – hide under rocks
Movement:
y Tube feet – sea stars and sea cucumbers
y Movable spines – urchins and sand dollars
y Swim – feather stars
y Flexible arms – brittle stars
Reproduction:
y Separate sexes – diecious
y External fertilization – up to 2,500,000 eggs per
season.
y Free swimming larva in plankton –bilateral
symmetry.
y Attaches by a stalk that degenerates when adult
forms. (except in crinoids).
Regeneration:
y Clam fisherman – fishermen in the past tried to kill
sea stars by chopping them into pieces but the more
they cut the more sea stars formed as they are able to
reproduce through fragmentation as long as part of
the ring canal was present.
Classes:
y Asteroidea – sea stars – intertidal zone
{ About 1,800 species
{ Often brightly coloured
{ Most are carnivorous, preying on bivalves and other
mollusks
{ Arms are short and thick with spacious coelomic cavities
containing gonads and branches of saclike digest system
Ophiurodea – brittle star and basket star
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Most abundant group with over 2,000
species.
Inhabit ocean floors worldwide, sometime
in the millions.
Arms are long and slender
Coelomic cavity, gonads, and digestive
system mostly confined to central disk
Mostly suspension or detritus feeders –
some carnivorous.
Echinoidea – sea urchins, sand dollars
y Spacious coelom containing 2 – 5 gonads and a
coiled digestive tract.
y Mostly mobile grazers feeding on algae (sea urchins)
or burrowing detritus feeders (sand dollars)
y All the plates of bear calcareous spines mounted on a
ball-and-socket joint that’s provided with muscles.
Echinoidea con’t
y Pedicellarias (A defensive organ like a minute pincer
present in large numbers on an echinoderm) of sea
urchins are more complex than those of the sea stars.
They are on tall moveable stalks and most have three
jaws. They are specialized for different functions –
defence, cleaning, and even feeding
Holothuroidea – sea cucumbers
y Soft to leathery, elongated bodies with microscopic
or larger scale like ossicles (A small piece of calcified
material forming part of the skeleton) in body wall
y Spacious coelom containing a single gonad and
coiled digestive tract.
y Buccal tube feet greatly enlarged as feeding tentacles.
y Sedentary suspension feeders or creeping or
burrowing detritus feeders.
Crinoidea – sea lilies and feather stars
y Like an upside down sea star with the mouth
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pointing up.
Branching arms with side branches (pinnules)
containing gonads and bearing tube feet.
Feed on tiny organisms and fine particles in the
water, and the outspread arms and pinnules form an
elegant food – collecting device.
Some feather stars move about constantly; others
remain in the same spot for months at a time.
Sea lilies are sessile.
Sea daisies
y The most recently discovered class of animals –
discovered in 1986.
y Live on sunken wood deep in the sea.
y Small animals, less than 1cm in diameter.
y No internal digestive system.
Echinoderms in the World
y Population explosions - crown of thorns are
destroying coral reefs.
y Food – Urchin eggs
y Anticancer and viral drugs