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Phylum Annelida the segmented worms The Higher Animals - two lineages • Higher animals have a coelom and a mouth/anus • The infolded blastopore of the forming gastrula can become either a mouth or anus • If it becomes: a mouth -> called protostomes anus -> deuterostomes blastopore True Coelom • Peritoneum (from mesoderm) lines the body wall and all organs- Totally enclosed by mesoderm. • WHAT ARE THE BENEFITS OF DEVELOPING A COELOM? • the ‘solid’ mesoderm of lower animals becomes inefficient as body size increased • Body cavity = fluid + space for specialized organs needed in circulation of waste / food Segmentation • Repeated body units (seperated by septum) with similar structures • Permits specialization of units Annelid Diversity Class – Oligochaeta (earth worms) Oligo = Few Chaeta = Bristles • Movement – circular and longitudinal muscles work together to produce “inching” wave-like movement called peristalsis – chitinous bristles (setae) on each segment help to anchor worm in soil • Feeding – Eat soil / decayed matter – Muscular pharynx sucks food through mouth then pushes it down to the esophagus and crop (storage) to a grinding organ (gizzard) then onto the intestine. – Blood transports nutrients digested in intestine – Wastes pass out anus – *** MPECGI *** http://www.ncsu.edu/scivis/lessons/earthworm/Overview.html Closed Circulatory System • Simple diffusion does not work for large animals. • Anterior muscular vessels (Aortic Arches) act as ‘hearts’ (5 Pairs) • Blood carries nutrients and gases through closed vessels to capillary beds • No lungs; gases diffuse across moist skin Excretory System • Paired nephridea pass through septum (partition) into posterior segment. Waste out pore. Nervous System • dorsal, anterior ganglion (primitive brain) • Ventral nerve cord; nerves to each segment • Can sense chemicals, light, touch Reproductive System • Hermaphroditic, but reproduce by copulation • Clitellum has gland cells which secrete cocoon to protect developing eggs Class - Polychaeta • Many-bristles • Marine worms • Each segment has parapodia (side-feet) – movement / gas exchange Class - Hirudinea • Leeches • parasites who bite into skin to feed • Can fast for up to one year Questions 1. What is the significance of MPECGI ? 2. What is the function of the clitellum? 3. What function do cetea/bristles? Explain. 4. For each class give a member: Hirudinea : Oligochaeta Polychaeta