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Hemichordata and Invertebrate Chordates Phylum Hemichordata Characteristics of Hemichordata:All live marine environments. Bilaterally symmetrical. Body divided into three sections, a proboscis, a collar and a trunk. Body cavity a true coelom divided into three cavities. Dorsal, sometimes tubular, nerve cord. Complete digestive tract, feeds on fine particles in the water. Class Enteropneusta Marine worms Ciliated epidermis and glands cover acorn worms Burrow in sandy and muddy substrates Common name ‘acorn worms’ Maintenance Functions Ventral Mouth Lateral Pharyngeal slits,few to several hundred Cilia and mucus assist acorn worms in feeding Ciliary tracts converge near the mouth and form a mucoid string that enters the mouth Enteropneusta extends its posterior end out of the burrow during defecation. Eww!!! Nervous system • Ectodermal in origin • Lies at the base of the ciliated epidermis • Consist of dorsal and ventral nerve tracts • No major ganglia • Sensory receptors are unspecialized Respiration • Simple diffusion of metabolic waste • Cilia associated with Pharyngeal slits circulate water into mouth and out of body • Gas exchange as water passes through pharyngeal slits Circulatory system • Colorless blood moves nutrients and wastes • Dorsal and ventral contractile vessel • Blood moves anteriorly in dorsal • Posteriorly in ventral vessel • Branches from theses vessels lead to open sinuses (Partially open circulatory system) • Anterior flowing blood moves through glomerulus (excretory organ) • Waste filtered into proboscis coelom and out through pores Reproduction and Development Dioecious!! External Fertilization pheromones Evolutionary ties b/w hemichordatres and echinoderms Ciliated larvae Class Pterobranchia pteron- wing branchia- gill Deep marine water Some live in shallow waters Body divided into three regions Size 0.1 - 5mm Individuals called zooids Most live in secreted tubes in asexually produced colonies Maintenance Functions Filter feeders Cilia on tentacles trap and transport Food to mouth Respiration and excretory exchange by diffusion Reproduction and Development Asexual budding is common and responsible for colony formation Also some posses one or two gonads Most species are dioecious External fertilization Planula-like larva (cnidarian) Settles to a substrate, forms cocoon and metamorphoses into an adult Phylum Chordata Characteristic of the chordates Deuterostome embryo development Notochord, phayngeal slits or pouches, dorsal tubular nerve cord, and postanal tail Coelomate animals Bilateral symmetry Endoskeleton Two major groups: nonvertebrate chordates and vertebrates Subphylum Urochordata • Uro, tail and chorda, cord • Class ascidians – Tunicates or sea squirts • • • • Solitaire or colonial Sessile adults Attach to solid substrates two siphons that permit seawater to circulate through the body • Oral siphon also the mouth • Atrial siphon Body wall • Tunic- gown • Connective tissue like covering • Tough secreted by the epidermis • Composed of proteins Salts, cellulose • Stolons extensions of tunic help root Maintenance Functions • Longitudinal and circular muscles below the body wall epithelium • Nervous system largely confined to body wall • Forms nerve plexus with a single ganglion between oral and atrial opening • Sensitive to mechanical and chemical stimuli around siphon but no complex sensory organs Reproduction and Development • Tadpole larva • Attaches to substrate by adhesive papillae located below the mouth • During development internal structures rotate 1800 bending the digestive tract into a Ushape Reproduction and Development • Monoecious • Self fertilization and cross fertilization Subphylum Cephalochordata • Elongated laterally flattened nearly transparent • Lancelets • Size up to 5 cm tadpole like animals • All four chordate characteristics persist throughout life • Shallow waters • genera Branchiostoma (Amphioxus) Reproduction and Development • Dioecious • Gonads shed gametes into the atrium • Leave the body through the atriopore • External fertilization • Bilaterally symmetrical larva • Larva free swimming • Larva Settle to substrate then metamorph into adults Maintenance Function • Filter feeders • Buried in sandy substrate • Mouth pointed upward • Cilia on lateral surfaces of gill sweep water into mouth • Food sorted in the cirri •Edible particles move along cilia to the gut • No true heart • Contractile waves in the walls of major vessels propel blood • Blood contains amoeboid cells and bathes tissues in open spaces • Excretory tubules are modified coelomic cells closely associated with blood vessels. • Coelom reduced- restricted to canals near the gill bars, endostyle and the gonads
