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ECHINODERMS
5-WAY SYMMETRY
“spiny-skinned”
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ECHINODERM
CHARACTERISTICS
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Radially symmetrical-adults
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Pentamerous – based on 5-parts
Bilaterally symmetrical- planktonic larvae
 No head
 No anterior/posterior end; no
ventral/dorsal side
 Refer to the oral and aboral side
 Complete digestive tract
 Well-developed coelom
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Endoskeleton
 Water-vascular system- waterfilled canals
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Tube feet- muscular extensions of canals
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Extended when filled with water- have muscular sacs
called ampullae
Used for movement, attachment, and receiving
chemical and mechanical stimuli
Madeporite- or sieve plate- in sea stars and
sea urchins; on the aboral side; where water
enters the water vascular system
BIOLOGY OF ECHINODERMS
Radial symmetry = sedentary life style
 Feeding and digestion- sea stars are
carnivorous; they extend their stomach
out through their mouth and excrete
digestive enzymes; the food is then
carried into the digestive gland and the
stomach moves back into the body; if
intestines are present, they are very small
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Brittle stars- no anus; very simple guts
Crinoids- simple guts
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Feeding and digestion cont.
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Sea urchins and sea cucumbers have long
coiled guts (sea urchins need this because they
are herbivores and the sea cucumbers need
this because they need to process sediment)
In all echinoderms, nutrients are passed in the
coelomic fluid within the coelom
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Also transports oxygen because they don’t have a
circulatory system
Sea cucumbers have respiratory trees- which are
thin, branched tubes that are connected to the gut
and extend out to the anus
NERVOUS SYSTEM AND BEHAVIOR- have
a nerve net- more complex actions than
cnidarians though
 REPRODUCTION AND LIFE HISTORY
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Separate sexes
External fertilization
Zygote develops into a ciliated larva
Some don’t have larva but brood their
offspring in specialized pouches
Some reproduce asexually by the separation of
the central disc or body into two piecesREGENERATION
TYPES OF ECHINODERMS
7000 KNOWN SPECIES- all marine
 Bottom dwellers
 1. Class Asteroidea= sea stars
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5 arms that radiate from central disk
Amulacral groove= the radiating channels on
the arms
Can move in any direction
Endoskeleton = interconnected plates of
calcium carbonate creating very flexible arms;
aboral surface may be covered with spines that
are modified into pincer like organs called
pedicellariae which helps to keep the surface
clean
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Asteroidea cont.
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Most are predators of bivalves, snails,
barnacles or other attached or slow moving
animals
Class Ophiuroidea= brittle stars; 5 arms
are very long and brittle
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Most eat detritus and small animals
Tube feet don’t have suckers, used for feeding
No anus
Most species (2000)
Indian Sea Star
Anthenea crassa
Sunflower Sea Star
Choriaster granulatus ,
the dough-boy star
Astropectin polyacanthus
Arctic Sea Stars eating
a Clam
Orange-banded Brittle Star (Ophiothrix)
Brittle star (Ophiocoma imbricatus)
Brittle star larvae
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CLASS ECHINOIDEA OR SEA URCHINS
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Endoskeleton forms a round, rigid, shell-like
test with movable spines and pedicellariae
Body forms a sphere
Mouth on bottom; anus on top
Graze on seaweeds and seagrasses
Have Aristotle’s Lantern- the set of jaws and
associated muscles used by sea urchins to bite
food
1000 species
Purple Sea urchin’s test w/o
spines
Purple Sea Urchin with spines
Pencil Sea urchin
Banded Sea urchin
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Class Echinoidea cont.
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Heart urchins and sand dollars have flattened
bodies and short spines
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They are deposit feeders using tube feet and mucus
to pick up particles
Heart Urchin with and without spines
Internal Sand dollar
Keyhole sand dollar with and without spines
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CLASS HOLOTHUROIDEA OR SEA
CUCUMBER
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Worm like
No spines and no obvious radial symmetry
Look stretched
Lies on one side where the 5 rows of tube feet
are; oral and aboral surface on the ends
Endoskeleton has microscopic spicules
Deposit feeders; tube feet around mouth are
modified into branced tentacles
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Class Holothuroidea cont.
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Defensive mechanisms
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Secrete toxic chemicals in filament
Might expel the gut or other internal organs; this is
called evisceration
Prickly red sea cucumber
Orange sea cucumber
Warty Sea cucumber
Sea cucumber eviscerating
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CLASS CRINOIDEA OR CRINOIDS
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Suspension feeders
Feathery arms
600 species of feather stars and sea lilies
Sea lilies are in deep water and attached to
bottom
Feather stars perch and crawl in both shallow
and deep water
An upside down brittle star with the amulacral
grooves and mouth facing upward
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Class Crinodea cont.
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Can have up to 200 arms
Passion flower feather star
Feather star
Sea lily
Sea lily reef