Phylum Echinodermata
MARINE INVERTEBRATES
Characteristics

All marine

Known as spiny-skinned animals

Endoskeleton known as the test is made
of calcium plates or ossicles with
protruding spines

Includes sea stars, brittle stars, sand
dollars, sea urchins, & sea cucumbers
Characteristics
Bipinnaria Larva

Undergo metamorphosis from bilateral,
free-swimming larva to sessile or sedentary
adult

Larval stage known as dipleurula or
bipinnaria

Adults have pentaradial (5 part) symmetry

Lack segmentation or metamerism
Characteristics

Coelomate

Breathe through skin gills as adults

Capable of extensive regeneration
Characteristics

Ventral (lower) surface called the oral
surface & where mouth is located

Dorsal (upper) surface known
as aboral surface & where anus is
located

Have a nervous system but no head
or brain in adults

No circulatory, respiratory, or
excretory systems
Characteristics

Have a network of water-filled
canals called the water vascular
system to help move & feed

Tube feet on the underside of arms
help in moving & feeding

One-way digestive system consists
of mouth with oral spines, gut, & anus

Deuterostomes (blastopore
becomes the anus)
Characteristics

Separate sexes

Reproduce sexually &
asexually
Includes 5 classes:

Crinoidea - sea lilies & feather stars

Asteriodea - starfish

Ophiuroidea - basket stars & brittle stars

Echinoidea - sea urchins & sand dollars

Holothuroidea - sea cucumbers
1) Crinoidea Characteristics

Sea lilies & feather stars

Sea lilies have a long
stalk with branching arms that attach
them to rocks & the ocean bottom

Feather stars can detach & move
around

Mouth & anus on upper surface
1) Crinoidea Characteristics

May have 5 to 200 arms with sticky tube feet to help capture food (filter
feeders) & take in oxygen

Common in areas with strong currents & usually nocturnal feeders
2) Asteroidea Characteristics

Usually sedentary along shorelines

Starfish or sea stars

Come in a variety of colors

Prey on bivalve mollusks such as clams & oysters
2) Asteroidea Characteristics
Have 5 arms that can
be regenerated
 Arms project from
the central disk
 Mouth on oral
surface (underside)
 Range in size from
1 cm to 1 m

Body Plan of Sea Star

Have an endoskeleton made of calcium plates

Sharp, protective spines made of calcium plates
called ossicles found under the skin on
the aboral (top) surface

Have pedicellariae or tiny, forcep-like structures
surrounding their spines to help clean the body
surface
Aboral Surface
Water Vascular System

Network of canals creating hydrostatic
pressure to help the starfish move

Water enters through sieve plate or
madreporite on aboral surface into a
short, straight stone canal

Stone canal connects to a circular
canal around the mouth called
the ring canal
Water Vascular System

Five radial canals extend down
each arm & are connected to
the ring canal

Radial canals carry water
to hundreds of paired tube feet
Water Vascular System
3) Class Ophiuroidea

Largest class of echinoderms

Includes basket stars & brittle
stars

Live on the ocean
bottom beneath stones,
in crevices, or in holes
3) Class Ophiuroidea

Have long, narrow arms resembling a tangle of snakes

Arms readily break off & regenerate

Move quicker than starfish

Feed by raking in food with arms or trapping it with its
tube feet
4) Class Echinoidea

Includes sea urchins & sand dollars

Internal organs enclosed by endoskeleton or test made of fused
skeletal plates

Body shaped like a sphere (sea urchin) or a flattened disk (sand
dollar)

Lack arms
4) Class Echinoidea

Bodies covered with movable spines

Have a jawlike, crushing
structure called Aristotle's lantern to
grind food

Use tube feet to move
4) Class Echinoidea

Spherical shape

Live on ocean bottom

Scrape algae to feed

Long, barbed spines make venom for
protection
4) Class Echinoidea

Flattened body

Live in sand along
coastlines

Shallow burrowers

Have short spines
5) Class Holothuroidea

Includes sea cucumber

Lack arms

Shaped like a pickle or cucumber

Live on ocean bottoms hiding in
caves during the day

Have a soft body with a
tough, leathery outer skin
5) Class Holothuroidea

Five rows of tube feet run lengthwise on the aboral (top) surface of
the body

Have a fringe of tentacles (modified tube feet) surrounding the
mouth to sweep in food & water

Tentacles have sticky ends to collect plankton

Show bilateral symmetry

Can eject parts of their internal organs (evisceration) to scare
predators; regenerate these structures in days
5) Holothuroidea

Bulb-like sacs or ampulla on the
upper end of each tube foot
contract & create suction to help
move, attach, or open bivalves

Rows of tube feet on oral surface
(underside) are found
in ambulacral grooves under each
arm
Feeding & Digestion

Tube feet attach to bivalve mollusk shells & create suction to pull valves
apart slightly

Starfish everts (turns inside out) its stomach through its mouth & inserts it into
prey

Stomach secretes enzymes to partially digest bivalve then stomach
withdrawn & digestion completed inside starfish