BIOL 1F90 Lecture 28: BIOL 1F90 lecture 28 winter 2016
15 Mar 2016
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Lecture 28: body cavity true coelom: boy cavity is completely lined with mesoderm (coelomates) Pseudocoelom: coelom is not completely lined by tissue derived from mesoderm (pseudocoelomates) Uid lled body cavity can protect internal organs or be used as hydrostatic skeleton. Presence or absence of segmentation traced to change in homeotic or hox genes. Deviations from traditional (morphology-based) phylogenies and modern (dna-based) Phylogenies: relationships among bilateria, presence or absence of a body cavity, relationships among bilateral traditionally split into deuterostomeia and protostomia base on embryonic development. Deuterostomes still separate by protostomes divided into lophotrochozoa and ecdysozo. All secret a nonliving cuticle strongly supported as a separate clade by molecular evidence such as similarities in dna. Bilateral symmetrical worms, strongly dorsoventrally attened include both free living and parasitic forms. Pseudocoelomates three layered body with uid lled pseudocoelom between endoderm and mesoderm lack circulator system. Ex. nematodes, rotifers, acanthocephalans (spiny-headed worms), horsehair worms.
