Phylum Echinodermata
Introduction
Echinodermata
• About 6000 species, all marine
Echinodermata
Major characteristics
• secondary
pentamerous radial
symmetry
internal skeleton
• water vascular
system
Water Vascular System
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Madreporite
stone canal
ring canal
radial canal
lateral canals
Ampulae
tube feet
CLASSIFICATION OF
ECHINODERMATA
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Class Asteroidea
Class Ophiuroidea
Class Echinoidea
Class Holothuroidea
Class Crinoidea
Class Asteroidea
True Starfishes
Class Asteroidea
• arms not sharply
delineated from
central disc
• tube feet with
suckers; used for
– Locomotion
– obtaining food
• madreporite and
anus aborally
located
• some have
pedicellariae jawlike appendages
of epidermis
True Starfishes
Class Asteroidea
True Starfishes
• Feeding
– Mouth
– cardiac stomachcan be extruded
– pyloric stomach
– pyloric caecae
– Anus
– feed primarily on
sessile organisms
Class Asteroidea
Systems
• Circulation
– poorly developed with fluid filled chambers;
– no heart;
coelom ciliated for fluid movement
• Excretion
– no special organs
– general diffusion across body surfaces like tube feet
• Respiration
– no special organs
– across body membranes
• Nervous System
– associated with epidermis
– circular oral nerve ring with branches into arms
Asteroidea
Body wall
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Epidermis- outer surface; includes
– mucous cells
– epithelium
– Pedicellariae- jawlike appendages of the epidermis
• can open and close
• used to clean body of debris or put debris on body
Dermis- includes
– nerve cells
– connective tissue
Skeleton- below dermis
– made of ossicles
– lattice like connections
– Calcium carbonate
– with spines and tubercles
Muscle layer- below dermis
Peritoneum that lines coelom
Asteroidea Reproduction
• are dioecious;
external
fertilization
• usually 10 gonads;
2 in each arm
• have fissiparitydivision of central
disc into two
animals
Asteroidea Reproduction
• free living larvae
• bipinnaria- first
larval form develops
into
• brachiolaria - shows
development of arms
Class Ophiuroidea
Brittle Starfishes
Class Ophiuroidea
Brittle Starfishes and Basket Stars
• 5 arms
usually
• central disc
well marked
off, no
branches of
gut in arms
Class Ophiuroidea
Brittle Starfishes and Basket Stars
• no anus, no
ambulacral groove
• madreporite on oral
surface
• no suckers on tube
feet, no ampullae
(have a valve to
control pressure)
• no pedicellariae
• able to move
quickly and snake
like hence their class
name
Class Echinoidea
sea urchins, sea bisquits, sand dollars
Class Echinoidea
• no arms
• skeleton is
fused into a
solid test
• tube feet have
suckers
• covered with
moveable
spines and
pedicellariae
Class Echinoidea
specialized mouth structures - Aristotle's Lantern
Class Holothuroidea
Sea cucumbers
Class Holothuroidea
Sea cucumbers
• body elongated
in oral-aboral
axis
• skeletal system
reduced or
absent
• no spines or
pedicellariae
• mouth and anus
at opposite ends
of body
Class Holothuroidea
Sea cucumbers
• no external
madreporite
• tube feet with suckers
• respiration through
anal respiratory tree
• dioecious; single gonad
• suspension or detritus
feeders
• commensal
relationship with pearl
fish
Class Crinoidea
Sea Lillies
Class Crinoidea
• most are extinct
• most primative
• all sessile, with
stalk that
attaches to
substrate
• have branched
arms for filter
feeding
• no suckers on
tube feet
• no madreporite
• no pedicellariae
Sea Lillies