BLG 316 Lecture Notes - Lecture 12: Hydrostatic Skeleton, Lophotrochozoa, Bilateria
19 Apr 2019
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Difference between annelida and mollusca - they have many segments, walls between them, no shell. Fluid is incompressible, 1 muscle contracts 1 must expand. Muscles need something to act against, transferring force of movement with fluid. If you are unsegmented (and only have longitudinal muscles) you can only whip back and forth (sinusoidal movement) Annelids have both muscle directions & walled compartments. = more precise targeted movement (less energy used) Each compartment surrounded by peritoneum lining body wall. Excretory tubes - remove waste from blood/coelom fluid to pores for excretion. On ventral side to help them dig in soil on that side. Cerebral ganglia - ring of nerves, connects to nerve cord. Synapomorphies: a characteristic present in an ancestral species and shared exclusively (in more or less modified form) by its evolutionary descendants. Also function as gills (rich blood supply - respiratory capillaries) Vermicomposting - they are excellent at breaking down decaying matter, important for soil quality.
