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25. Hemichordates Nov 30

25. Hemichordates Nov 30 - Phylum Chateognatha arrow worms...

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1 Phylum Chateognatha arrow worms ~ 70 spp almost all planktonic All marine Predators - important components of plankton indicator species for different water masses, important predators on copepods, larvae, fish larvae Most 1.5 - 3 cm, some up to 10 cm Body 3 parts: Head, Trunk, Tail Head: vestibule => mouth teeth chitinous spines hood eyes Trunk - largest part of body pharynx intestine – supported by mesentaries divide coelom into left and right posterior anus body wall – muscle bands bends for rapid swimming/ attack no excretory system Female reproductive system and genital openings Head Trunk Tail Tail: separate coelom, divided left & right by septum 2 Tests Seminal Vesicles Spermatophores
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2 Nervous System: ventral ganglia eyes mechano- and chemo- receptors Feeding: raptorial predators Reproduction and Development: hermaphroditic mutual transfer of spermatophores Direct development Radial cleavage Mesoderm enterocoelous Deuterostomes Evolutionary position unknown at present Dunn et al. 2008 place with Protostomes, sister to Lophotrochozoa Developmentally they are Deuterostomes Phylum Hemichordata Phylum Hemichordata Two classes So different that some consider them separate Phyla We will consider them together Pterobranchia Enteropneusta PHYLUM HEMICHORDATA Anteriorly directed diverticulum of buccal cavity 3 body divisions – each with a coelom Pharynx – gill slits Marine 2 Classes - Enteropneusts – large, burrow - Pterobranches – small, in tubes CLASS ENTEROPNEUSTA 3 Body Divisions- each with a coelom Proboscis Collar Trunk
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3 Sacoglossans free living Proboscis : muscularized, used for burrowing protocoel = coelomic space - opens via proboscis pore Collar : ventral mouth buccal cavity buccal diverticulum = stomocord runs anterior into proboscis proboscis skeleton (elastic plate) coelom = mesocoel right and left, each w/ a posterior duct Trunk: coelom = metacoel , divided left & right, no openings outside Anterior = pharyngeal region GILL SLITS U-shaped, tongue like bars skeletal support external pores – separated by epidermis from gill slits Pharynx Gill Slits U-Shaped Respiration Collect Food
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4 Pharynx – collects food and water passes out Dorsal Pores – simple not U-shaped posterior to pharynx Gut diverticula - visible from outside Terminal anus Feeding: burrow ciliary mucus Nervous System: no ganglia Dorsal and Ventral nerve cords Nerve Rings Fragile – good at regenerating trunk Circulatory System: blood – pigments, amoebocytes open – vessels and sinuses GLOMERULUS : in Proboscis coelom - excretory function - associated w/ blood system ! Pressure filtration wastes enter proboscis coll. and exit via pores all vessels pump gas exchange across body, not concentrated in pharynx Reproduction and Development dioecious gonads – each with pore, pharyngeal region external fertilization Radial cleavage Deuterostome Larval type: TORNARIA similar to some echinoderm Bipinnaria & Auricularia
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5 Pterobranchs Live in Tubes CLASS PTEROBRANCHIA small, <1 cm historically thought to be all deep water now found in
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