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Echinoderms
Thu Truong
Phylum: Echinodermata
"echino" - sea urchin, "spiny"
"derm" - skin
Example animals:
Starfish
Brittle Star
Sea Urchin
Sand dollar
General Characteristics
• Larvae - Bilateral Symmetry, cilliated, free-swimming
• Adults - Pentaradial Symmetry
• Endoskeleton - consists of calcium carbonate plates and spines,
w/ thin cilliated epidermis
• Pedicellariae - modified spines, pincer-like, keeps surface clean
• Water Vascular System - network of fluid-filled canals that
function in locomotion, feeding, and gas exchange.
• Branches of the WVS become extended when filled with fluid
(tube feet)
• Ampulla - round muscular sac at the base of the foot,
stores fluid and operates tube foot
• Well developed coelom, but no excretory organs.
• Digestive system most prominent, simple nervous system
• Sexes are separate, both eggs and sperm are released into water
Class: Crinoidea
• Anatomy
o Stalk - makes them sessile
o "arms" resemble feather structure
• Feeding/Behaviors
o Remove suspended food from water
o Oral surface is on upper side of disk
o Tentacles coated with mucus to capture organisms
Class: Asteroidea
• Anatomy
o Central disk, has 5 to more than 20 arms - tube feet underneath
o Mouth lies on underside of the disc
o Endoskeleton - series of calcareous plates, enables limted
movement, moves slowly
• Feeding/Behaviors
o Carnivorous, eats by attaching itself to prey and secretes
digestive enzymes
• Gas Exchange/Secretion
o Poorly developed circulatory system, rely mainly on coelom
and coelomic fluid
o Wastes are diffused outside through the tube feet and dermal
gills
• Reproduction
o Sexual or Asexual
Class: Ophiuroidea
• Anatomy
o Bodies similar to asteroidea, but the arms are more slender,
enables it to move quicker
o Tube feet not used in locomotion
• Feeding/Behaviors
o Tube feet used to collect and handle food
Class: Echinoidea
• Anatomy
o Have NO arms, skeletal plates are flattened into a solid shell
called a test
o Sand dollars have flat bodies adapted for burrowing
o Sea urchins have bodies covered with spines, move by tube feet
• Feeding/Behaviors
o Sand dollars feed on tiny organic particles in sand
o Sea urchins feed on algae on the ocean floor with
calcareous teeth
Class: Holothuroidea
• Anatomy
o Elongated flexible body (muscular sac), mouth surrounded by
circle of tentacles (modified tube feet)
o Reduction of endoskeleton to microscopic plates
o Highly developed Circulatory system, transports oxygen +
nutrients
• Feeding/Behaviors
o Slow, live on bottom floor
o Eviscration - digestive tract, respiratory structures, and gonads
ejected from body (unfavorable conditions)
• Response to Stimuli
o if irritated will attack (shoots red tubules)