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Download Annelida 2010 - The Bronx High School of Science
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“Radiata” Metazoa Ancestral colonial flagellate Deuterostomia Eumetazoa Protostomia Bilateria Phylum: Annelida Nematoda Nemertea Rotifera Arthropoda Annelida Mollusca Platyhelminthes Chordata Echinodermata Brachiopoda Ectoprocta Phoronida Ctenophora Cnidaria Porifera Phylum: Annelida “segmented worms” earthworms, bristle worms, leeches •bilateral symmetry, triploblasts, protostomes, coelomates •main advance is segmentation (metamerism) •body composed of series of fused rings •segments (and coelom) separated by septa •repeated structures and organs Earthworm anatomy Phylum: Annelida Class: Oligochaeta earthworms •Named for relatively sparse “chaetae” (setae) or bristles found on eahc segment, made of chitin •Includes earthworms and some aquatic species •earthworms eat their way through the soil, extracting nutrients as soil passes through alimentary canal •valuable to farmers •till & aerate soil •fecal castings improve soil texture Phylum: Annelida earthworms, sandworms, leeches •well-developed complete one-way (mouth to anus) digestive system, tube within a tube •mouth- found on protostome (1st segment) •pharynx- muscular, sucks in soil •esophagus •crop- stores food •gizzard- muscular w/ small stones, grinds food •intestine- chemical digestion, nutrient absorption •anus Phylum: Annelida Class: Oligochaeta earthworms •well-developed excretory system with repeated structures, two per segment •metanephridia (primitive kidney) •excretory tubule open at both ends •network of small blood vessels closely associated •nephrostome at one end of tubule •ciliated funnel collects fluid from coelom •excretory pore (nephridiopore) at other end of tubule •dilute urine (urea) exits to outside body Phylum: Annelida Class: Oligochaeta earthworms •circulatory system • closed with unidirectional flow of blood • 5 aortic arches-muscular vessels that pump blood (“hearts”) • dorsal blood vessel supplies blood to posterior • ventral blood vessel returns blood to anterior • hemoglobin dissolved in blood increases capacity to carry oxygen Phylum: Annelida Class: Oligochaeta earthworms •nervous system •cerebral ganglia at anterior end comprise brain •ventral nerve cord runs length of animal •segmental ganglia originate from ventral nerve cord, 2 per segment Phylum: Annelida Class: Oligochaeta earthworms •reproduction •sexual •most are hermaphrodites (monoecious) •clitellum (thick band on epidermis) is site copulation •sperm transferred from male pore on clitellum •“cocoon” secreted by clitellum encases fertilized eggs that develop to juvenile worms •one mating yields 2 pregnancies in hermaphrodites Phylum: Annelida Class: Oligochaeta earthworms •locomotion •circular and longitudinal muscles •hydrostatic skeleton (fluid filled coelom, cuticle) •setae on each segment •chitinous bristles •embedded in epidermis •waves of muscular contractions shorten/lengthen animal •secrete mucus to lubricate path Earthworm anatomy Members of Phylum Annelida Class Oligochaeta •means “few setae” (bristles) •earthworms (Lumbricus terrestris) & relatives •many terrestrial, some aquatic Members of Phylum Annelida Class Polychaeta •sandworms, bristle worms •pair of parapodia w/ “many setae” (bristles) per segment •parapodia are fleshy paddle-like extensions •highly vascularized for gas exchange •used as gills & for locomotion •reproduction •lack clitellum •free-swimming trochophore larva •mostly marine Members of Phylum Annelida Class Hirudina •leeches •named for “hirudin”, the anti-coagulent secreted into host •also secrete anesthetic that prevents host from feeling attachment •feed on blood •historical medical use in bloodletting •not all bite, many feed on dead or dying tissues or animals, on open wounds •terrestrial and aquatic species Phylum Annelida: The Table- selected entries not covered Cleavage/cells: radial and determinate; egg is small with elsewhere little yolk Respiratory system: cutaneous breathing; skin must be kept moist for diffusion of oxygen; in Polychaeta parapodia act as external “gills” Relationship to other phyla: Mollusca- mesoderm origin, larval characteristics, cleavage pattern Arthropoda- segmentation, type of cuticle, nervous system Chordata- coelom segmentation
