Download Echinoderms

GENERAL CHARACTERISTICS
• Ex: sea stars, brittle stars, sand
dollars, sea urchins, & sea
cucumbers
• All marine
• “Spiny-Skinned
Animals” -
meaning
• Radial Symmetry as adults – 5
parts
• Regenerate = Autotomy
GENERAL MORPHOLOGY
• A. INTERNAL SKELETON of calcareous (made of calcium)
ossicles (plates)
• Variations :
Brittle / Sea Stars – many small plates that move with
one another
Sea Urchin & Sand Dollar – skeleton plates fused into
shell called “test”
Sea Cucumber – degenerated & buried in leathery body
B. Water Vascular System
• Used in locomotion, food capture, & respiration
• Network of canals – run throughout body ending
w/tube feet
• Varying internal water pressure can extend or
contract tube feet
• Tube feet end in small suction cups
C.
• Mouth on oral surface
(bottom / ventral)
• Anus on aboral surface
(top / dorsal)
ECHINODERM TYPES
SEA STARS
• 5 Arms / Rays 4 – 10”
• Prey on bivalves (clams,
mussels) & coral
• Many eat w/stomach
outside body; pop
stomach out mouth
Body Plan
• 2 – 4 rows of tube feet on each ray extend from
ambulacral groove
• Have pedicellariae or tiny,
forceps-like structures on
aboral surface to pick up
& remove dirt
Water Vascular System
• Water enters
madreporite on aboral
surface into a short,
straight stone canal
• Stone canal connects to
circular canal around
the mouth = ring canal.
• Enters five radial canals
extending down each
arm
Water Vascular System
• Radial canals carry
water to hundreds of
paired tube feet.
• Bulb-like sacs or
ampulla on tube feet
contract & create
suction
Other Body Systems
• No circulatory, excretory, or
respiratory systems
• No head or brain
• Eyespots on the tips of each
arm detect light
Reproduction
• Separate sexes
• External fertilization
• Females produce
200,000,000 eggs /
season; meroplankton
(their larval stage is
planktonic)
BRITTLE STARS
• Most mobile; fast
• Snake-like movement
• Disc is .4 – 1.2 “; arms are 2 –
2.4 “
• Scavengers
• In the largest class (with
basket stars)
• Arms break off readily
BRITTLE STAR LARVA
SEA CUCUMBERS
• Lack arms & visible
spines; elongated
• Flexible, leathery body
• Burrowers
• 5 rows of tube feet run
length of body
• 10-30 modified tube feet
form tentacles
around mouth
• Tentacles have sticky
ends to trap
plankton; or eat
detritus
• Breathes through anus
• Eject internal organs to
scare predators
(evisceration) ;
regenerate in days
•Symbiosis with Pearl Fish
which lives in its anus.
•Feed on gonads by day
Sea lilies & feather stars
• Filter Feeders
• Can detach & move around
Sea Urchins
• Spines for protection,
moving, trapping food
• Shell = test
• Divided into 10 sections
• 5 Ambulacral w/tube feet
• 5 Interambulacral without
• Covered w/muscle &
skin to help mobility
• Tube feet – moving, capturing food
• Pedicellarea – cleaning & defense
• Aristotle’s Lantern – 5 teeth together like bird’s beak;
to scrape algae from rocks
Sand Dollars
• Flattened version of urchin
• Live in sand along coastlines
• Food falls between dense
spines & carried to mouth by
cilia & tube feet
• Tiny, moveable spines for
burrowing
• Aristotle’s Lantern
Sea Biscuits
• Not as flat as dollars
• Live in sand along
coastlines; burrow
• Tube feet for respiration
• Pedicellarea
• Eat detritus in sand
• Short dense spines for
movement cover
test