Phylum Onychophora

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Phylum Onychophora
The velvet worms

• David Scarsella
• May 12, 2003
• Biology 235

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Phylum Onychophora
Family Peritopsidae
Family Peripatidae

• Australia, New Zealand
• Oviparous (eggs laid outside body)

• Widespread in tropical lands
• Viviparous (placenta)

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
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Onychophoran anatomy
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
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Drawings courtesy biodidac.bio.uottawa.ca
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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

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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 victims
  tissues

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Fossil record
Aysheaia pedunculata (Middle Cambrian, 520 mya)
Helenodora inopinata, 300 mya
Xenusion
www.ucmp.berkeley.edu/onychoph/onychophora.html
thenaturalcanvas.com/Mazoncreek/index_2.html
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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

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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
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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
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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
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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 2581345-1348   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. 11421-60
New, T.R. 1995. Onychophora in invertebrate
conservation priorities, practice and prospects.
Zoo. Jour. Linn. Soc. 11477-89   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
www.ucmp.berkeley.edu/onychoph/onychophora.html  
Onychophora Online rbt.ots.ac.cr/onych/index.htm