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Classical hypothesis Molecular hypothesis
Ado
utte
200
0 P
NA
S
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Schizocoelous development (typical of the protostome coelomates)
Protostome:Embryonic blastopore becomes mouth
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Enterocoelous development (typical of the deuterostome coelomates)
Deuterostome: Embryonic blastopore becomes anus. Mouth forms as secondary opening
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Cleavage
Spiral- third division and subsequent are unequal…typical of protostomes
Radial- third division is equal…typical of deuterostomes
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4 Deuterostome phyla*
• Echinodermata (sea stars, urchins, crinoids, et al.)
• Hemichordata (acorn worms, pterobranchs, extinct graptolites)
• Urochordata (tunicates, salps)
• Chordata (cephalochordates, vertebrates)
* Some authors place urochordates in Chordata
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Phylum Echinodermata
~7,000 extant species in five well-defined clades,
~13,000 extinct species and ~15 more classes.
• Asteroidea (starfishes)• Ophiuroidea (basket stars and brittle stars),• Echinoidea (sea urchins, sand dollars, sea
biscuits)• Holothuroidea (sea cucumbers). • Crinoidea (sea lilies and feather stars),• Concentricycloidea (sea daisies; 2 species),
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Synapomorphies of Echinoderms
1. Calcite skeleton composed of ossicles.
2. Water vascular system.
3. Mutable collagenous tissue.
4. Pentaradial body organization in adults.
Also exclusively marine, coelomate, and deuterostome
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Echinoderm water vascular system
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• Mainly carnivorous – evert stomach to carry out digestion without ingestion.
• Locomotion mainly by tube feet- arms move only slowly
• Arms are short and thick, with coelomic extensions containing digestive glands and gonads
Class Asteroidea (sea stars)
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Class Asteroidea (sea stars)
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Class Asteroidea (sea stars)
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Asteroidea, cont.
• Respiratory gas exchange via ciliated dermal papillae and coelomic fluid.
• Haemal (“blood”) system – function not understood.
• Capable of extensive regeneration and asexual reproduction in some classes
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Class Asteroidea (sea stars)
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A seastar (Asterias) opening a bivalve
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• Most diverse class of echinoderms- ~2,000 species.
• Distinct central disc containing the organ systems.
• Five highly flexible arms, capable of rapid movement by muscle action
• No anus. Deposit, detritus, and suspension feeders.
Class Ophiuroidea (brittle stars)
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Class Ophiuroidea (brittle stars)
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Class Echinoidea (sea urchins, et al.)
• Globular or flattened echinoderms without arms
• Complex 5-part jaw apparatus (“Aristotle’s Lantern”)
• Mainly grazers on algae, a few feed on bryozoans or sponges.
• Some species harvested as food (the roe is eaten)
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Aristotle’s Lantern – 50 ossicles
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• Endoskeleton reduced
• Elongated, flexible body propelled by 3 of the 5 rows tube feet
• Tube feet around mouth are enlarged and branched to form feeding tentacles that gather food and transfer to mouth.
• Gut has branches for respiration, and Cuvierian threads for defense.
Class Holothuroidea (sea cucumbers)
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Class Holothuroidea (sea cucumbers)
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Class Holothuroideasea cucumbers
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Class Holothuroidea (sea cucumbers)
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Class Crinoidea (crinoids)
• exaggerated, branched arms used for suspension feeding, oral side up
• Globular body (calyx) partially encased in skeletal plates
• Feather stars (unstalked) and sea lilies (stalked, attached).
• Greatest diversity in Paleozoic, with secondary radiation in Mesozoic after near-extinction
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Class Crinoidea (crinoids)
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Cyclonema on Glyptocrinus
Commensal snail that fed on crinoid feces
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Crinoid calyces from the Burlington limestone
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M. C. Barnhart
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M. C. Barnhart
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M. C. Barnhart
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M. C. Barnhart
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Echinoderm diversity thru time
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There are at least 15 described extinct classes of Echinodermata
The Class Homoiostyelia was world-wide in distribution.
They had a flexible tail, presumably for locomotion, and an arm for handling food.