Transcript Annelida
Phylum Annelida Adapted from Lesser Known Protostome Phyla. SICB 2001. J.R. Garey. Possess trochophore larvae Mollusca and Annelida are closely allied phyla Porifera Cnidaria Ctenophora Platyhelminthes Gastrotricha Gnathostomulida Cycliophora Rotifera Annelida Mollusca Sipuncula Nemertea Bryozoa Brachiopoda Phoronida Arthropoda Onychophora Tardigrada Nematomorpha Nematoda Priapulida Kinorhyncha Loricifera Echinodermata Hemichordata Chordata Arthropoda Mollusca Chordata Platyhelminthes Nematoda Annelida Porifera Echinodermata Other Sarcomastigophora Apicomplex Ciliophora Phylum Annelida: 12,500 spp: 3 classes = Class Polychaeta (8000 spp) Class Clitellata; subclass Oligochaeta (3500 spp) subclass Hirudinea (630 spp) Annelid characteristics • • • • Trochophore larvae Closed circulatory system True coelom Annuli refer to segmented, metameric body plan – Each segment has metanephridia, branches of nerves and blood vessels, chitinous setae / chaetae – Segments partially divided by septa → efficient hydrostatic skeleton → Pre-adapted for regional specialization and tagmatization Metamerism Septa provide regional control over hydrostatic skeleton Circular musc. Longitudinal musc. setae From this pic, know: metameric repetition of body segments (septa, metanephridia, nerves, blood vessels), modest cephalization, limited regional specialization Polychaeta • Mostly marine • Errant and sedentary spp Possess parapodia: Capillaries for gas exchange Swimming Crawling Burrowing setae acicula = chitinous rods for support Cephalization Jaws Ocelli (photoreceptors) Tentacles: Mechanoreceptors Chemoreceptors Tube worms: The sedentary polychaetes Parapodia reduced (no acicula, vascularization) Feathery appendages at anterior end for feeding, gas exchange Giant tube worms • Discovered in 1977 • Ocean floor 8000 ft deep • 4 ft tall • No mouth. Get food from endosymbiotic bacteria that feed on sulphur released at deep sea vents Polychaete reproduction Separate sexes 1. Conventional sexual reproduction: • Sperm + egg released into water → trochophore larva 2. Epitoky: – Epitokous individual forms an epitoke by a. Transformation of posterior portion b. Asexual budding – Mature indiv = atoke – Gamete-bearing part = epitoke capable of swimming about in search of mates (timed w lunar cycle) atoke epitoke Class Clitellata • Possess cylindrical ring used in reproduction – Formation of a cocoon for the embryos • Permanent gonads • Two subclasses: 1. Oligochaeta 2. Hirudinea Oligochaeta • • • • • Mostly fossorial, some aquatic little cephalization No specialized organs for gas exchange Feed on detritus, organic debris Hermaphroditic – Sperm exchanged between two mating individuals Sperm exchange between mating earthworms: • Sperm from testis stored in, and later released from, seminal vesicles • Sperm from other worm stored in seminal receptacles • After separation, sperm from other worm used to fertilize eggs from the ovary • Eggs and sperm from other worm released into forming cocoon • Many terrestrial forms can be parthenogenic Hirudinea • Occur in freshwater or moist terrestrial habitats • Highly streamlined • No special organs for gas exchange, sensory except ocelli • Have 2 suckers for feeding, locomotion – 3-toothed jaws • Ectoparasitic, but many are predaceous or scavenge Leech reproduction • Reproduction similar to oligochaetes (use of clitellum to form cocoons) Class(?) Echiura: spoon worms • Have trochophore larva but lack segments or any indication of metamerism as adults • Briefly segmented period as embryos • Molecular data links Echiura to Annelida • Reproduction similar to polychaeta -140 spp -Marine -Burrow in sand, mud