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8. Pseudocoelomates and Annelid Intro

8. Pseudocoelomates and Annelid Intro - Reminder from last...

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1 Phylum Nemertea Nemertea Pseudocoelomate Phyla Reminder from last week Intro to Phylum Annelida - lab this week Phylum Nemertia Phylum Nemertia ribbon worms ribbon worms (= (= Rhynchocoela Rhynchocoela) Similar to flat worms Similar to flat worms Acoelomate Acoelomate (?), Organ Grade Ciliated Epithelium Ciliated Epithelium Protonephridial Protonephridial Excretory system Excretory system Nervous system w/ sense organs Nervous system w/ sense organs Unlike flatworms Unlike flatworms one way gut (mouth & anus) one way gut (mouth & anus) closed closed circulatory system proboscis proboscis Special Features: Proboscis - complex organ Stylet - inject neurotoxins, glad cells subdue prey Rhynchocoel = proboscis cavity eversion - hydrostatic pressure - contraction of muscles in wall of proboscis sheath withdrawn - retractor muscle Fluid filled cavity for proboscis = Rhynchocoel Proboscis is everted by hydrostatic pressure It is retracted by contraction of the proboscis muscle The stylet has toxins to immobilize and kill prey Digestive System / Nutrition predators one way gut mouth => gut => anus allows specialization sequential digestion & absorption Nervous system brain - 2 nerve cords - lateral with connections many sensory structures
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2 Circulatory System Circulatory System Closed Closed - lateral blood vessels, lateral blood vessels, dorsal vessel & sinuses large vessels contractile transports nutrients, O 2 , hormones, waste, etc. Excretory System Excretory System Protonephridia - close assoc. with circulatory close assoc. with circulatory system system Reproduction Simple Dioecious Free Spawn (external fertilization) Development - direct or indirect - Pilidium Larva Asexual Repro - fragmentation very good at regeneration Evolution: Relatives of flatworms ? Similarities due to convergence? Is the circulatory system a modified coelom? Some phylogenies indicate they gave rise to chordates ? proboscis -> notochord? Still a big mystery!!! Development used to try to gain insight...
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