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Introduction to the Body-Plan of Onychophora and Tardigrada

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Introduction to the Body-Plan of Onychophora and Tardigrada Joakim Eriksson, 02.12.13 Animal bodyplans Onychophora Tardigrada Bauplan, bodyplan • A Bauplan is a set of conservative characters that are typical for one group but distinctively different from a Bauplan of another group Arthropoda Bauplan 2 Bauplan 3 Bauplan 4 Tardigrada Onychophora Euarthropoda/Arthropoda Insects Chelicerates Myriapods Crustaceans Arthropoda/Panarthropoda Bauplan 1 Arthropod characters • Body segmented, with limbs on several segments • Adult body cavity a haemocoel that extends into the limbs • Cuticle of α-chitin which is molted regularly • Appendages with chitinous claws, and mixocoel with metanephridia and ostiate heart (absent in tardigrades) • Engrailed gene expressed in posterior ectoderm of each segment • Primitively possess a terminal mouth, a non-retractable proboscis, and a thick integument of diverse plates Phylogenomics and miRNAs suggest velvets worm are the sister group to the arthropods within a monophyletic Panarthropoda. Campbell L I et al. PNAS 2011;108:15920-15924 Fossil arthropods, the Cambrian explosion Aysheaia An onychophoran or phylum of its own? Anomalocaris A phylum on its own? Crown group and stem group Arthropoda Bauplan 2 Bauplan 3 Bauplan 4 Tardigrada Onychophora Euarthropoda/Arthropoda Arthropoda/Panarthropoda Bauplan 1 How do arthropods relate to other animal groups Articulata Georges Cuvier, 1817 Characters uniting articulata: •Segmentation •Ventral nerv cord •Teloblastic growth zone Ecdysozoa Aguinaldo et al 1997 Ecdysozoa Character uniting ecdysozoa: •Body covered by cuticle of α-chitin Willow N. Gabriel et al •Cuticle periodically shed Developmental Biology Volume 312, Issue 2 2007 545 - 559 (ecdysis) http://dx.doi.org/10.1016/j.ydbio.2007.09.055 •Phylogeny based on nucleotide sequences Tardigrada • Tardigrades, waterbears, Bärtierchen • More than 1000 species described • Samll size 50 µm-1.2 mm • Marine, fresh water, terrestrial in water films • Separate sexes with internal or external fertilisation, parthenogenesis • Segmented • Moth with piercing stylets • Four pairs of legs Tardigrade anatomy • Segmented ventral ganglionic chain • Brain • “eyes” • Respiratory system: none, diffusion (Miniaturization) • Circulatory system: absent (Miniaturization) • Excretory system: some have malphigian tubes connected to the gut • Muscular pumping pharynx Cryptobiosis • Temperatures as low as -200 °C (-328 °F) and as high as 151 °C (304 °F) • Freezing and/or thawing processes • Lack of oxygen • Lack of water • Levels of X-ray radiation 1000x the lethal human dose • Boiling alcohol • Low pressure of a vacuum • High pressure (up to 6x the pressure of the deepest part of the ocean). • Space travel A tardigrade tun Fossil tardigrades • Middle Cambrian Siberia (530 Mya) • Cretaceous amber (60-80 May) http://tardigrades.bio.unc.edu/ Onychophora • Velvet worms, Peripatus, Stummelfüsser Onychophoran general info • About 150 species described • 5-200 mm, 13-43 pair of legs • Soft body • Segmented • Predators • Tropics and temperate areas of the southern hemisphere Onychophoran defining characters • Oral papillae with slime gland • Trachea (convergent with insects) • Water repelling skin with papillae • Simple eyes with secreted lens Distribution of two families Peripatidae Peripatopsidae Fossil onychophorans • Carboniferous, Mazon Creek (300 Mya) • Tertiary, Baltic and Dominican amber (30- 40 Mya) Poinar, 2000 Onychophorans are found in moist environments, e.g. decomposing wood Onychophoran anatomy Spinous pads Claws The appendages of the head • Antenna • Jaw • Slime papilla Internal anatomy Excretion • Segmental organs: metanephridia with coelomic vesicle (sacculus) Circulation • Dorsal heart with open circulatory system Musculature • Body musculature: circular, oblique, longitudinal and transverse • Muscles operating the appendages Cross section Onychophoran heart, body muscles Onychophoran nephridia Transverse muscle VNC Bladder Excretory duct Onychophoran nephridia VNC Transverse muscle Sacculus Onychophoran brain Onychophoran eye Reproductive sytems Female reproductive organs, ovary, oviducts and uteri with developing embryos Onychophoran ovary, oviduct, uteri Ovary Uterus Embryo Uterus Onychophoran testis and seminal vesicle Seminal vesicle testis Reproductive strategies • Oviparous • Ovoviviparous • Viviparous • Fertilisation internal, spermatophors delivered to genital tract or to body surface. • Development very long, 1 year Practicals Onychophora Tardigrada • Sections: draw cross section • Try to identify legs, eye and identify internal organs: spots, mouth stylets and CNS, slime gland, salivary gland, nephridia, gut, muscles pharynx • Details of nephridia and body • Identification of species wall with muscles • Alcohol specimens: draw details of feet with claws, head appendages • Demo: genitalia, brain, Live specimens .
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