BI256 Lecture Notes - Lecture 8: Kidney, Osmoregulation, Planaria
Document Summary
Lecture 8 flatworms part 1 jan 20th 2017. Two major evolutionary advances: cephalization, primary bilateral symmetry. Also triploblastic and either acoelomate or pseudocoelomate. Placed at base of bilateral animal tree. Small flat worms < 5mm in length. Typically live in marine sediments: few pelagic, some species live in brackish water. Most free living; some commensal, some parasitic. Digestive system: mouth tube like pharynx sack like gut (incomplete) Mouth an endodermally derived mass of cells/ syncytial mass. In many acoels, the gut and pharynx are absent. Diffuse system of anterior neurons connected to radially arranged nerve cords, instead of a ladder like pattern seen within phylum platyhelminthes. Lophotrochozoan formed from merging the words lophophore and trochophore. Lophophore: crown of ciliated tentacles: efficient feeding device, used for respiration. Trochophore larva: free swimming, feeding, with ring of large ciliated cells in front of mouth (prototroch) Members (should) have in common either a lophophore or trochophore larva.
