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SYNOPTIC DESCRIPTION OF THE PHYLUM ONYCHOPHORA

SYNOPTIC DESCRIPTION OF THE PHYLUM ONYCHOPHORA (GRUBE 1853)

EUKARYA> UNIKONTA> OPISTHOKONTA> ANIMALIA> BILATERIA> PROTOSTOMATA> ECDYSOZOA> PANARTHROPODA> ONYCHOPHORA
ONYCHOPHORA LINKS

Introduction

Hierarchical Classification

The following information came from Margulis and Schwartz (1998), Buchsbaum (1938), Barnes (1980), Barnes (1984), Brusca and Brusca (2003), Hickman (1973), Meglitsch and Schramm (1991), Ruppert and Barnes (1991), Storer and Usinger (1965), and Tudge (2000).

I. SYNONYMS: velvet worms, onychophorans.

II. NUMBER: >80 to ~200 species known.

III. PHYLUM CHARACTERISTICS:

  • A. Structure
    • Symmetry: Bilateral
    • Body Cavity: Coelomic pouches greatly reduced to gonoducts and excretory ducts. Most of the cavity made of haemocoel.
    • Body Covering: Covered by a thin cuticle (text with tooltip) Cuticle is an acellular covering that is secreted by the epithelium in animals. It also is the waxy material, made of cutin, on the outside of plants. with tubercles in rings or bands. No superficial segmentation of the cuticle.
    • Support: Hydrostatic skeleton made by sinuses of haemocoel (text with tooltip) A haemocoel is the primary body cavity of arthropods and related organisms. It is characteristic of organisms with an open circulatory system in which the blood 'circulates' in a large open sinus that surrounds the organs. .
    • Digestive System: Anteroventral mouth flanked by two oral papillae and surrounded by perioral lobes. Food tube simple with terminal anus. Capture food by secretion of sticky threads from oral papillae (text with tooltip) Oral papillae are paired finger-like appendages on either side of the mouth, which release a sticky substance used to capture prey in onychophorans. . Threads entangle prey.
    • Circulatory System: Open. With a long, segmented dorsal heart and a large haemocoel cavity.
    • Locomotion: Move by many pairs of unjointed, stubby legs, each terminates in a pair of claws.
    • Excretory System: Pared metanephridia opening by their own ducts at each internal “segment”. Anterior nephridia modified to salivary glands; posterior nephridia modified to gonopores.
    • Nervous System: Brain attached to paired ventral nerve cords attached at ladder-like ganglionic swellings. Eyes, sensory antennae and other sensory swellings.
    • Endocrine System: None.
    • Respiratory System: Small tufts of minute tracheae (text with tooltip) Trachea (tracheae, pl.) is the windpipe of vertebrates, the air-filled tubes in most arthropods. each opening by a spiracle (text with tooltip) Spiracles are openings on the abdominal segments of insects and body segments of myriapods through which air enters the tracheal system. It also is a small circular gill slit in some chondrichthyes. .
  • B. Reproduction:
    • Reproductive System: Dioecious (text with tooltip) Dioecious organisms have separate male and female individuals. . A few with external fertilization; most with internal fertilization. Oviparous (text with tooltip) An oviparous (adj.) animal is one that releases eggs in its life cycle. They may be fertilized internally or externally. , ovoviviparous, and viviparous (placenta attaches embryo to uterus wall).
    • Development: Large yolky eggs (in oviparous forms) cleave superficially (text with tooltip) Superficial cleavage is the incomplete and unequal cleavage of the zygote. . Direct development.
  • C. Ecology: Free-living terrestrial animals that inhabit leaf litter, stream banks and other areas of high humidity. Usually nocturnal predators.
LITERATURE CITED

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Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass.

Buchsbaum, R. 1938. Animals Without Backbones, An Introduction to the Invertebrates. The University of Chicago Press. Chicago.

Budd, G. 1993. A Cambrian gilled lobopod from Greenland. Nature. 364: 709-711.

Budd, G. E. 1998. Arthropod body plan evolution in the Cambrian with an example from anomalocaridid muscle. Lethaia. 31: 197-210.

Budd, G. E. 2001. Tardigrades as ‘Stem-Group Arthropods’: The evidence from the Cambrian fauna. Zool. Anz. 240: 265-279.

Dunn, C.W., A. Hejnol, D.Q. Matus, K. Pang, W.E. Browne, S.A. Smith, E. Seaver, G.W. Rouse, M. Obst, G.D. Edgecombe, M.V. Sørensen, S.H.D. Haddock, A. Schmidt-Rhaesa, A. Okusu, R.M. Kristensen, W.C. Wheeler, M.Q. Martindale, and G. Giribet. 2008. Broad phylogenomic sampling improves resolution of the animal tree of life. Nature. 452: 745-749.

Dzik, J. and G. Krumbiegel. 1989. The oldest ‘onychophoran’ Xenusion: a link connecting phyla? Lethaia. 22: 169-182.

Eriksson, B. J. and G. E. Budd. 2000) Onychophoran cephalic nerves and their bearing on our understanding of head segmentation and stem-group evolution of Arthropoda. Arthropod Structure and Development. 29: 197-209.

Garey, J. R. 2001. Ecdysozoa: The relationship between Cycloneuralia and Panarthropoda. Zoologischer Anzeiger 240: 321-330.

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Lartillot, N. and H. Philippe 2008. Improvement of molecular phylogenetic inference and the phylogeny of Bilateria. Phil. Trans. R. Soc. B. 363: 1463-1472.

Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3rd Edition. W. H. Freeman and Company. New York.

Mayer, G. 2006. Structure and development of onychophoran eyes: What is the ancestral visual organ in arthropods? Arthropod Structure and Development. 35: 231-245.

Mayer, G. and P. M. Whittington. 2009. Velvet worm development links myriapods with chelicerates. Proc. R. Soc. London B. 276: 3571-3579.

Monge-Najera, J. 1995. Phylogeny, biogeography and reproductive trends in the Onychophora. Zoological Journal of the Linnean Society. 114: 21-60.

Nicholas, W.L. 2001b. The pseudocoelomate Ecdysozoa. In: Anderson, D.T., ed. Invertebrate Zoology. Oxford University Press. Oxford, UK. pp. 98-119.

Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford.

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Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York.

Ruppert, E. E. and R. D. Barnes. 1994. Invertebrate Zoology. 6th edition. Saunders. Ft Worth, TX.

Strausfeld, N. J., C. M. Strausfeld, R. Loesel, D. Rowell, and S. Stowe. 2006. Arthropod phylogeny: onychophoran brain organization suggests an archaic relationship with a chelicerate stem lineage. Proc. R. Soc. London. B. 273: 1857-1866.

Telford, M. J. S. J. Bourlat, A. Economou, D. Papillion, and O. Rota-Stabelli. 2008. The evolution of Ecdysozoa. Phil. Trans. R. Soc. B. 363: 1529-1537.

Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York.

Waggoner, B. M. 1996. Phylogenetic hypotheses of the relationships of arthropods to Precambrian and Cambrian problematic fossil taxa. Systematic Biology 45(2): 190-222.
By Jack R. Holt and Carlos A. Iudica. Last revised: 02/03/2013
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