Transcript Annelids
Annelids Segmented Worms Key Terms Septa – internal walls between segments Seta – bristles attached to each segment Crop – organ where food is stored Gizzard – organ where food is ground into small pieces Closed circulatory system – blood is contained within a network of blood vessels that run from head to tail Key Terms Gill – an organ specialized for breathing underwater Nephridium – excretory organs that filter fluid in the coelem Clitellum – band of thickened, specialized segments Annelids Body Diagram Feeding Could be filter feeders or predators Get their food through the pharynx Earthworms gets food through the pharynx which pumps food into the crop and gizzard for grinding and digestion. Food is absorbed in the digestive tract in the organ called the intestine. Respiration, Circulation and Excretion Respiration occurs across their skins Aquatic annelids may breathe through the gills Annelids have a closed circulatory system in which blood is contained in a series of blood vessels. Excretion includes digestive wastes that are passed through the anus. Cellular wastes are processed through the nephridia that filter fluid in the coelem. Defense and Response Most annelids have little defense mechanisms. Most annelids have a well developed nervous system that includes a brain and several nerve cords running through the body from head to tail. Reproduction Most annelids reproduce sexually. Some use external fertilization and have separate sexes. Most are hermaphrodites but do not fertilize themselves. Worms will attach to each other and exchange sperm into special sacs. During fertilization, the clitellum secretes a mucus ring into which the sperm and eggs are released. Fertilization takes place in this ring. Worms Classes of Annelids Oligiochaetes – such as an earthworm Have relatively few setae compared to other classes. Most live in fresh water or soil. Classes of Annelids Polychaetes – marine annelids that have paired, paddle-like appendages tipped with setae. Includes sandworms, bloodworms and their relatives. Classes of Annelids Hirudina – external parasites that suck the blood and body fluids of their host. Includes leeches which have suckers at both ends of their bodies. Secrete anti-coagulants to prevent the blood from clotting so they can feed. If they feed well, they may crawl into a cool place and not feed again for months. Ecology of annelids Worms are important for soils. By burrowing through the soils, they aerate it and mix it thoroughly to about 2 meters. These tunnels allow oxygen into the soil which the growth of beneficial bacterial and fungus in the soils. Aquatic worms are an important food source in the food web. Review Question 1 In earthworms, the clitellum is used for A. digestion B. excretion C. reproduction D. respiration C. Reproduction Review Question 2 In the earthworm, waste created by cellular metabolism is eliminated by the A. Crop B. Nephridia C. Gizzard D. Flame cell B. Nephridia Conclusion Annelids are worms with segmented bodies. They have a true coelom that is completely lined with mesoderm. Oligochaetes are annelids that typically have streamlined bodies and relatively few setae ocmpared to ploychaetes. Most oligochaetes live in soil or water. Leeches are typically external parasites that suck the blood and body fluids of their host. References Biology textbook - dragonfly