BIOL 1604 Lecture Notes - Lecture 11: Hirudo Medicinalis, Clitellum, Oligochaeta
Document Summary
Includes marine bristle worms, earthworms, leeches, freshwater worms. Segmented worms metameric, often with a distinct head: serial repetition of similar body units along the anteroposterior axis of the body, each segment is a metamere or somite. Hydrostatic compartments: coelom well developed and generally divided by septa. Paired epidermal-chitinous setae present (lost in leeches) Digestive system complete and not segmentally arranged. Body has outer circular and inner longitudinal muscle layers. Nervous system with double ventral nerve cord and a pair of ganglia. Brain is a pair of dorsal cerebral ganglia with connectives to ventral nerve cord. Specialization of head region into differentiated organs, such as tentacles, palps, eyespots of polychaetes. Excretory system typically a pair of nephridia for each segment. Respiratory gas exchange through skin, gills or parapodia. Circulatory system closed with muscular blood vessels and aortic arches (hearts) for pumping blood segmentally arranged. Asexual reproduction by fission, fragmentation or budding.
