AnnelidaSlides - marine polychaetes Phylum Annelida the...

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9/28/11 1 Phylum Annelida - the segmented worms - marine polychaetes, earthworms, leeches, & marine “beardworms” ~15,000 living (“ extant ”) & ~200 fossil species bilaterally symmetric ; ~ 0.5 mm to 3 m long; organ-level of organization beard worm terrestrial, freshwater & marine environments swim, burrow into or crawl across a substrate predators or scavengers some are ectoparasites (leeches) earthworm leeches marine polychaetes annelids have an extensive fossil record back to the Cambrian “Canadia” Cambrian fossil from Burgess Shale serpulid fossilized worm tubes Cambrian fossil trochophore larvae discovered 1998 (FYI only) Annelids are important in marine ecosystems… - involved in nutrient redistribution through burrowing: - they convert organic debris into CO 2 , which dissolves in water and is taken up by marine phytoplankton for photosynthesis, releasing O 2 Sabellidae Sabellidae serpulid tube worm Eunice sp.
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9/28/11 2 ecosystems: earthworms redistribute nutrients & help soil drainage & aeration (recall video: Scottish fields became flooded when invasive flatworm destroyed the native earthworm population; also see text box p. 212, 4 th th eds.) Meet “Joe” earthworm. Annelids are: - protostomes - lophotrochozoans the deuterostome - protostome split Ectoprocta Phylogenetic placement of Annelida within Metazoa Please note : aside from the lophophorate phyla last time, annelids are the first major group of coelomates we have dealt with in this course. Ectoprocta As protostomes , annelids have schizocoelous coelom formation. Coelom : a fluid-filled body cavity completely enclosed by mesoderm
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9/28/11 3 Key innovation with annelids: metamerism http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb6pg2.htm Annelids are metameric : the body is a series of repeating segments , or metameres. METAMERISM : division of the body into distinct, serially repeated coelomic segments or “compartments” (metameres) metameres are separated externally by circular rings, or annuli metameres are separated internally by septa components of major body systems - excretory, circulatory, reproductive & nervous - are repeated in (mostly) each segment - the gut is the only exception (it runs all the way through segments) annulus (external “ring”) …so there is a greater need to have a system to transport materials; i.e., a closed circulatory system that can traverse the segments. evolutionary significance of metamerism : permits greater flexibility, complexity, & larger size, leading to greater species diversity But metamerism introduces a “problem”: coelomic fluid in non -metameric phyla can be used to transport nutrients and wastes (e.g., pseudocoelomates), but there are now septa acting as barrier… a dorsal vessel pushes blood forward (anteriorly) a ventral vessel moves blood posteriorly capillary beds connect the two major blood vessels in the body wall
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AnnelidaSlides - marine polychaetes Phylum Annelida the...

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