3454chapter15

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Unformatted text preview: Chapter 15 : Pseudocoelomates (Phylum? Achelminthes) Phyla Rotifera and Nematoda (also Gastrotricha, Kinorhyncha, Loricifera, Priapulida, Nematomorpha, Acanthocephala, and Entoprocta, Cycliophora) Have a pseudocoelom—cavity around gut with no mesoderm around gut No muscles around gut limits them to small size Food moved through gut by cilia or packing from one end with a pharynx Flow through gut with mouth and anus Protostomous, triploblastic Freshwater, marine, terrestrial or parasitic Dioecious Phylum Rotifera—rotifers Characterized by a wheel organ or corona— feeding and swimming structure 1800+ species Marine or freshwater filterfeeders Foot with pedal glands to adhere to substrate Show eutely—having a set, constant number of cells in the body Species-specific number Have protonephridia similar to platyhelminths with flame cells Bilobed brain with paired nerves for sensory and motor functions Paired eyespots Bimodal reproductive cycle—asexual and sexual (fig. 15-19, p. 308) Amictic females reproduce asexually in stable conditions Produce diploid eggs Mictic females produce haploid eggs when crowded, starved, heated, etc. Eggs may become haploid males (which produce sperm to fertilize other eggs) Fertilized eggs become dormant until conditions improve Phylum Nematoda—Nematodes or roundworms Cylindrical, no cilia/flagella, longitudinal muscles only, eutely Approximately 500,000 species (12,000 described) They live everywhere in huuuuuuuuuuge numbers Millions per cubic meter of sediment/topsoil in some places Predatory, detritivorous,...
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