BI236 Lecture Notes - Lecture 6: Symmetry In Biology, Radial Nerve, Trochophore
Document Summary
Biology bi256 life on earth : animals; flatworms. Phylum acoelomorpha: placed at base of bilateral animal tree, ~350 species, small flat worms <5 mm in length, typically live in marine sediments; few - pelagic. Some species live in brackish water: most free-living; some commensal, some parasitic, bilateral symmetry, body flattened dorsoventrally, triploblastic, acoelomate (atypical !, have a cellular ciliated epidermis, asexual reproduction by fragmentation, monoecious, no excretory or respiratory system. Digestive system: (cid:373)outh tu(cid:271)e-like phar(cid:455)(cid:374)(cid:454) sa(cid:272)k-like gut (incomplete) In many acoels, the gut and pharynx are absent. Mouth a(cid:374) e(cid:374)doder(cid:373)all(cid:455) deri(cid:448)ed (cid:373)ass of cells / syncytial mass. Nervous system: a(cid:272)oelo(cid:373)orphs la(cid:272)k a (cid:862)true(cid:863) (cid:271)rai(cid:374). La(cid:272)k ga(cid:374)glio(cid:374) (cid:894)(cid:373)ass of (cid:374)er(cid:448)e (cid:272)ell (cid:271)odies(cid:895): diffuse system of anterior neurons connected to radially arranged nerve cords, instead of a ladder-like pattern seen within phylum platyhelminthes. Schematic drawing of the nervous system of: pulchra. (cid:862)brai(cid:374)(cid:863) i(cid:374) gree(cid:374) (cid:373)age(cid:374)ta a(cid:374)d cyan. Lophotrochozoan formed from merging the words lophophore and trochophore.
