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Download Section 13.2 – Segmented Worms Characteristics Annelids Setae
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Section 13.2 – Segmented Worms Characteristics Annelids - Setae – Bristle-like structures that worms use to hold on to the soil and to move - Bilateral symmetry - Body cavity with organs - A mouth and an anus - Examples – earthworms, marine worms and leeches Earthworm - Most well known Annelid - Anterior – front end - Posterior – back or hind end - More than 100 segments - Body segments have 4 pairs setae except for the first and the last segment - Crop – Stores food and soil - Gizzard – Grinds food and organic matter Trace Food Through the Earthworm 1) Mouth 2) Esophagus 3) Crop 4) Gizzard 5) Intestine 6) Anus - Earthworm waste piles are called Castings Closed circulatory system 5 Aortic Arches that pump blood O2 and CO2 are exchanged through moist skin Front segment – brain Main nerve cord connects to brain Respond to light, temperature and moisture Hermaphrodites Marine Worms - More than 8,000 species - Have segments with setae that occur in bundles - Some are sessile - Free swimming have a head with eyes, tail and parapodia – fleshy outgrowths that aid in feeding and locomotion Leeches - Do not have setae - Feed on blood of animals - A sucker at each end of body attaches to animal - Produces an anesthetic that numbs the wound - Can such 2-10 times its weight in blood - Sometimes leeches are used after surgery Value of Segmented Worms - Aerate soil - Speed up return of nitrogen to soil - Being used to develop drugs - Food Origin - Evolved in the sea - 620 million years old - Mollusks and segmented worms have a common ancestor
