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Phylum Annelida Annelus = “ Little Ring” The Segmented Worms www.onacd.ca 3 Major Classes in Phylum Annelida Class Oligochaeta: the earthworms Class Hirudinea : The leeches Class Polycheata: The marine worms Identifying Characteristics of the Annelids Have a TRUE COELOM (body cavity which allows them to have true organ systems and muscular layers) Posses complex digestive & circulatory systems as well as defined nervous and excretory systems No developed respiratory system as they exchange O2 and CO2 via moist epidermis Are segmented into a sequence of compartments by septa. Segments are marked by rings called annuli Reproduce sexually and some asexually by regeneration and fission Are hermaphroditic with cross fertilization Are found in terrestrial, freshwater and marine environments Can range in size from less than 1 mm to over 3 meters (the seep tube worm) Example: The Earthworm - Digestive system is a one way tube including a mouth and anus with specialization of digestive organs (esophagus, crop, gizzard, and intestines) - Closed circulatory system with blood contained in blood vessels. Presence of a primitive heart and hemoglobin in the blood to carry O2 - Excretory system includes nephridia (primitive kidneys) which eliminate waste from the blood - Nervous system includes cephalization with a primitive brain and ventral nerve cord. No defined sensory organs Earthworm Reproduction Although earthworms are hermaphroditic (produce both eggs and sperm) they must still copulate in order to mix their gametes Earthworms are also capable of regrowing amputated segments of their bodies Mating Earthworms Ecological Importance of Annelids Oligochaete Worm Form the base of many food chains House parasites such as Protozoa, Platyhelminthes and Nematodes Aerate & mix the soil and are constructive to mineralization and nutrient uptake by vegetation Certain species mix the surface and mineral soil by traveling between the two Biological Roles include: acting as composters and helping to create dead organic matter into fertile soil Chemical Roles include: helping to cycle nutrients and minerals through the soil through their casts (worm poop!) Increasing the levels of nitrogen, phosphates and potash Physical Roles include: burrowing and keeping the soil structure open (aerating the soil and providing a path for drainage) Random Annelid Facts In the New Zealand Maori culture NOKE is an earthworm dish sold as a delicacy Lumbriculus and Aulophorus (species of annelids) are known to reproduce by the penis breaking into fragments and then forming whole new worms!