SYSTEMATIC BIOLOGY | KINGDOM ANIMALIA |
PHYLUM ONYCHOPHORA |
INTRODUCTION TO THE ONYCHOPHORA
Onychophora (o-ne-KO-fo-ra) is formed from two Greek roots that mean "claw bearers" (claw -nichi (νύχι); and bearer -phoros (φόρος). The reference is to the small claws at the ends of the telescoping legs.
The velvet worms look like annelids with telescoping legs (Figure A). Now they mainly inhabit terrestrial environments that are high in humidity. However, their fossils (i.e. Hallucigenia of the Burgess shale fauna; Figure B) indicate that they once occupied marine benthic environments. They are part of a larger natural group known as the panarthropods (Mandibulata, Chelicerata, Tardigrada, and Onychophora; Brusca and Brusca 2003, and Nielsen 2001). Brusca and Brusca (2003) summarize a large body of literature on the panarthropods and indicate that the onychophorans have generally been considered a sister group to the tardigrade-"arthropod" line. Nielsen (2001) suggests that the specializations of the living onychophorans (tracheae, specialized nephridia, and slime glands) show that the extant line is from a specialized offshoot of the Paleozoic marine fauna.
FIGURE A. Peripatus, a living onychophoran. |
FIGURE B. Hallucigenia, an onychophoran from the mid-Cambrian Burgess Shale. |
Images taken from: A: http://www.museums.org.za/bio/onychophora/ B: http://www.nmnh.si.edu/paleo/shale/phallu.htm |
SYNOPTIC DESCRIPTION OF THE PHYLUM ONYCOPHORA
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 species known. III. PHYLUM CHARACTERISTICS:
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HIERARCHICAL CLASSIFICATION THE ONYCHOPHORA
The onychophorans today are but a remnant of a former diverse group. Thus, they like the priapulids, have a problematic taxonomy. Meglitsch and Schram (1991) recognize taxa no higher than the family level. Most other sources (e.g. Brusca and Brusca 2003; Ruppert et al. 2004) do not even attempt to present a taxonomy. I have given a provisional taxonomy with a single class (Onycophorida) and a two orders: Paronynychophora (all extinct) and Euonychophora. |
CLASS ONYCHOPHORIDA (2 ORDERS)
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LITERATURE CITED
Barnes, R. D. 1980. Invertebrate Zoology. Saunders College/Holt, Rinehart and Wilson, Philadelphia.
Barnes. R. S. K. 1984a. Kingdom Animalia. IN: R. S. K. Barnes, ed. A Synoptic Classification of Living Organisms. Sinauer Associates, Inc., Sunderland, MA. pp. 129-257.
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.
Hickman,
C. P. 1973. Biology of the Invertebrates. The C. V. Mosby Company.
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.
Meglitsch, P. A. and F. R. Schramm. 1991. Invertebrate Zoology. Oxford University Press, New York, Oxford.
Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford. [L]
Ruppert, E. E., R. S. Fox, and R. D. Barnes. 2004. Invertebrate Zoology: A Functional Evolutionary Approach. Seventh Edition. Thomson, Brooks/Cole. New York. pp. 1-963.
Storer,
T. I. and R. L. Usinger. 1965. General Zoology. 4th Edition. McGraw-Hill Book
Company.
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.
By Jack R. Holt. Last revised: 02/07/2010 |