Download Phylum Echinodermata

Phylum
Echinodermata
Ch.16
Phylum Echinodermata
• ~7,ooo Species
• Triploblastic, coelomate, ALL marine
• Pentaradial symmetry
– (Body parts arranged in fives or a multiple of five)
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Complete Digestive Tract
Regeneration
Most are dioecious, some are moneocious
Most use external fertilization
Water-vascular system (Figure 16.4)
– Madreporite  Stone canal  Ring canal  5
radial canals branch off  Lateral canals  Tube
feet
Class Asteroidea
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Sea stars, about 1,500 species
May be brightly colored with red, orange, or blue
Most have 5 arms that radiate from central disc
Oral surface down and in middle
Dermal branchiae in skin (gas exchange)
Water-vascular system
Suction disks of tube feet are used for attachment and
movement
• Sea stars feed on snails, bivalves, crustaceans, corals, and a
variety of other food items
• Are well known for regeneration, they can regenerate any part
of a broken arm….an entire sea star can be regenerated from a
broken arm IF the arm contains a portion of the central disk…it
is a slow process, taking up to a year for complete
regeneration.
Class Ophiuroidea
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Greek for snake (orphis) tail (oura) in the form of (oeides)
Brittle stars & Basket stars, over 2,000 species
Most diverse group of Echinoderms
Are predators and scavengers
The mouth leads to a sac-like stomach, and no part of the digestive
tract extends into the arms
Water-vascular system used for capturing prey, not for locomotion
Tube feet lack suction cups, successive ossicles articulate and are
acted upon by large muscles to produce snake like movement (hence
the name of the class)
Like sea stars, ophiuroids can regenerate lost arms. If a brittle star is
grasped by an arm, the brittle star will cast off the arm, this process
called autonomy (Greek: autos=self + tomos=to cut) is used in
escape reactions!
Dioecious, and males are generally smaller than females.
Class Echinoidea
• Sea urchins, sand dollars, about 1,000 species
• Sea urchins live on hard substrates, sand
dollars live in sand or mud
• Feed on dead animal remains, plankton, algae
• Aristotle’s lantern – 35 teeth-like ossicles (a
chewing apparatus) used in feeding
• Urchins – hard surfaces, move by spines and
tube feet, some have venom
• Sand Dollars – burrow just below surface
Class Holothuroidea
• Sea cucumbers, about 1,500 species
• Found at all depths of the ocean, and crawl or burrow
• Have no arms, and they are elongated along the oral-aboral
axis and have enlarged tube feet around mouth.
• Are ~10-30 cm in length
• Ingest organic matter, use tentacles
• Edible – “trepang” in Asia (body wall boiled and dried)
• Water-vascular system internal & has coelomic fluid
• Mostly sea cucumbers are defenseless against prey…but….
– Many produce toxins that discourage predators
– Some eject sticky internal tubules that contain toxins (from
the anus) to confuse predators
– Some cause internal structures to explode (basically blowing
up their body) in response to chemical and physical stress
as a defensive adaptation to discourage predators,
regeneration of lost parts follows!
Class Crinoidea
• Feather stars, sea lilies, about 230
species
• Most primitive of all echinoderms
• Many species in fossil record
• Attach permanently to a substrate and
filter water for plankton
• Sea lilies attached by a stalk
• Feather stars have no stalk
• Feather stars swim by raising and
lowering arms