phylum onychophora n.
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Phylum Onychophora

Phylum Onychophora

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Phylum Onychophora

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  1. Phylum Onychophora The velvet worms David Scarsella May 12, 2003 Biology 235

  2. Australia, New Zealand Oviparous (eggs laid outside body) Widespread in tropical lands Viviparous (placenta) Phylum Onychophora Family Peritopsidae Family Peripatidae More than 100 described species Carnivores, herbivores, omnivores; nocturnal All extant species are terrestrial; though fossil onychophorans are primarily from marine sediments Exhibit sexual dimorphism

  3. Onychophoran anatomy 1 Defining characteristics: 1) Jaw-forming appendages 2) Oral papillae 3) Slime glands discharge glue from oral papillae 4) Subcutaneous hemal channels-part of hydrostatic skeleton 2 Drawings courtesy

  4. Onychophoran locomotion • Propulsion generated by musculature of limbs; body remains rigid • Limbs elevate body above ground • Several waves of limb activity progress down body length concurrently • Constant volume hydrostatic skeleton (hemocoel) serves as prop for limbs

  5. Adhesive glands • Thought initially evolved for use in defense • Hunting adhesive only known in this phylum and some arachnids • Attack prey by shooting glue from a distance through oral papillae, then onychophoran can bite through protective coverings and liquify victim’s tissues

  6. Fossil record Aysheaia pedunculata (Middle Cambrian, ~520 mya) Helenodora inopinata, ~300 mya Xenusion

  7. What are they? • Annelid: Excretory system; no joined appendages; hydrostatic skeleton • Arthropod: Respiratory system; embryology; chitin-containing cuticle • Onychophorans: Diffuse nervous system; adhesive glands; legs are soft, plump and not jointed, and ‘walk’

  8. Evidence from 12S Ribosomal RNA Sequences That Onychophorans are Modified Arthropods • Onychophorans have been described as the missing link between arthropods and annelids • Findings: Data suggests that onychophorans form a sister group to chelicerates and crustaceans plus hexapods; also onychophorans are a highly specialized assemblage, thus not a ‘outgroup’ or missing link J.W.O. Ballard et al. Science 258: 1345-1347

  9. Fossil Velvet Worms in Baltic and Dominican Amber • Slime production mechanism establishes a minimum time for evolution; thus connecting terrestrial Dominican fossil (20-40 mya) to extant species • Baltic fossil (40 mya) is evidence for extensive range in the past (Eocene); perhaps subtropical Poinar, George Jr. Science 273: 1370-1371

  10. Onychophoran conservation • Onychophora merit conservation both per se and as members of communities (habitats) sensitive to change • Populations of many species appear to be small and of low density; distinct evolutionary interest may render susceptible to overcollecting • Future prospects: habitat security, regional evaluation of taxonomic status, legal protection, captive breeding, education, ‘umbrella taxa’ New, T.R. Zoo. Jour. Of Linn. Soc. 114: 77-89

  11. References Ballard, J. W. O., O. Ballard, G. J. Olsen, D. P. Faith, W. A. Odgers, D. M. Rowell and P. Atkinson. 1992. Evidence From 12S Ribosomal RNA Sequences that Onychophorans are Modified Arthropods. Science 258:1345-1348 Buchsbaum, Ralph. 1987. Animals Without Backbones, 3rd ed. Chicago: University of Chicago Press, 456-460 Ghiselin, M. T. 1984. Peripatus as a living fossil. Pages 214-217 in Living Fossils (N. Eldredge and S. M. Stanley, eds.) Springer-Verlag, New York. Monge-Najera, J. 1995. Phylogeny, biogeography and reproductive trends in the Onychophora. Zoo. Jour. Linn. Soc. 114:21-60 New, T.R. 1995. Onychophora in invertebrate conservation: priorities, practice and prospects. Zoo. Jour. Linn. Soc. 114:77-89 Pechenik, Jan A. 2000. Biology of the Invertebrates, 4th Ed. New York: McGraw-Hill, 402-406 Poinar, George, Jr. 1996. Fossil Velvet Worms in Baltic and Dominican Amber: Onychophoran Evolution and Biogeography. Science 273: 1370-1371 Willmer, Pat. 1990. Invertebrate Relationships: Patterns in animal evolution. Cambridge: Cambridge University Press Introduction to the Onychophora Onychophora Online