Echinodermata
Echinodermata
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Approx. 6,000 known species; all marine
Deuterostomes
Pentamerous radial symmetry
Endoskeleton – calcareous ossicles
Tricoelomate
Water-vascular system
Mutable connective tissue
Reproduction – External Fertilization,
larval
If radially symmetrical – why placed so
“high” on evolutionary tree?
• Radial symmetry is
secondarily derived trait
– Evolutionary influences?
– Benthic lifestyle
• Water-vascular system
• Bilateral symmetry in
larvae
• Metamorphose to radial
Endoskeleton
• Composed of ossicles
• Ossicles linked or diffuse
• Small or large plates – one
of features that
distinguishes classes
Mutable Connective Tissue
• Dermis, extracellular
matrix
• Changes in Ca+2
concentration
• Rigidity through matrix
• Movement of urchin
spines
Regeneration
• Most echinoderms
capable of regeneration
• Totipotent cells
• Mutable connective tissue
– Brittle star losing arm
– Cucumbers regurgitating
viscera
Tricoelomate
• Three pair of coelomic pouches
(characteristic of deuterostomes)
• One forms water vascular system
Water-Vascular System
• Point of inflow
• Series of canals
(formed from
mesocoel)
• Tube feet
• Functions by changing
pressure
Water-Vascular System
• Ampulla
• Muscle/suction
• Adhesion largely
chemical
• Release
Circulatory System
• Closed
• “ebb and flow”
• Lymph system – Tiedemann’s bodies –
linked to WVS
Class Asteroidea
• Sea Stars
• 1,500 known species
• Central disc, radiating
arms
• Ossicles – connected,
shape varies w/ sp.
• Pedicellariae (see Fig.
28-10 an 28-11) defense
• Mucus secretion and
cilia – keep surface clean
Cross Section (Arm)
Digestive System
Class Ophiuroidea
• Brittle Stars, Basket
Stars
• 2,000 known species
• Central disc, arms
distincly set off
• Ossicles – Plates
• “Vertebrae” in arms
• Lack pedicellariae
and cilia
Calcareous plates and shields
Locomotion
• Most mobile of Echinodermata
• “rowing”
Class Echinoidea
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Urchins, sand dollars
~950 known species
Name means “like a hedgehog”
No arms, circular or oval in shape
Some members have secondary bilateral
symmetry
• Ossicles – flattened and sutured to form a
test
Spines
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Primary (long) and secondary (short)
Ball and socket
Movement by muscular sheath
Mutable connective tissue locks in place
Water Vascular System
• Essentially like a sea stars
• Madreporite is a modified genital plate
• Circumpharyngeal ossicles
and muscles
• Protrusible
• Highly muscularized
• Used of grazing
Holothuroidea
• Sea cucumbers
• 1,200 species
• Greatest habitat
diversity of
Echinoderms
• Most 10 – 30 cm
• Range 5 mm – 2 m
• 1/3 species live
deep ocean (90%
biomass
Holothuroidea
• Elongate on oralaboral axis
• No arms
• Buccal podia
• Micro-ossicles