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- 1) The lophophorates include phyla with traits of both deuterostomes [tri-coelomate body, radial cleavage, blastopore yields anus (e.g., brachiopods), coeloms via enterocoely (some)] & protostomes [larval protonephridia (some), mouth from blastopore (e.g., bryozoans)]
a) most are sessile with a reduced head & most secrete a protective covering or shell; almost all are suspension feeders
b) two unifying traits are: i) a lophophore (crown of ciliated tentacles around the mouth extended by the mesocoel), ii) a U-shaped gut (anus typically lies outside lophophore)
c) Ph. BRYOZOA (moss animals) ~4,000 marine & freshwater spp; encrusting colonial animals with polyp-like zooids that extend out of a gelatinous, leathery or calcareous exoskeleton; particles are captured by lateral cilia or tentacular flicking
d) Ph. BRACHIOPODA (lamp shells) ~300 marine spp; solitary animals enclosed by paired (dorsal & ventral) shells & bearing a stalk-like pedicle; a coiled lophophore maximizes feeding efficiency vs rate; most went extinct 225 MYA; some have a blind gut (no anus!)
- 2) Ph. HEMICHORDATA (acorn worms) ~100 marine spp; the phylum is pivotal to our understanding of chordate origins
a) two classes differ greatly in form & may belong in separate phyla
b) the Cl. Pterobranchia are tube-dwelling, colonial animals with a well developed lophophore; feeding resembles bryozoans; zooids exhibit a clear tri-partite body and move about in the tubes on a creeping oral shield; gill slits are small (one pair) or absent
c) the Cl. Enteropneusta (acorn worms) are sediment-dwelling animals that also exhibit a clear tri-partite body; an extensive branchial chamber, with ciliated U-shaped gill slits, is very similar to that in SubPh. Cephalochordata (sister group to the vertebrates)
d) most enteropneusts feed on particles in sediment; some may filter feed; which mode is primitive remains unclear
- 3) Echinoderms and hemichordates share several traits:
a) a protocoelic nephridium (=axial complex)
b) a coelomopore (=hydropore) connecting the protocoel to the outside of the body
c) similar larval forms (echinoderm auricularia & bipinnaria resemble the enteropneust tornaria) & arrangement of major coeloms
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Copyright © 2002 by A. Richard Palmer. All rights reserved.
(revised April 4, 2002)