Phylum ONYCHOPHORA

Onychophora

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Phylum ONYCHOPHORA

Velvet Worms

Compiler and date details

1 December 2000 - A.L. Reid, Eltham, Victoria, Australia

Introduction

Onychophora are soft-bodied terrestrial invertebrates, commonly known as velvet worms. Worldwide, they are found mainly in the Southern Hemisphere, and only in tropical and subtropical regions in the Northern Hemisphere. Two families are recognised: Peripatidae, with some 75 species, and Peripatopsidae, with around 90 species. Peripatids are pantropical whereas, with the exception of one species, peripatopsids occur in the Southern Hemisphere only, with many in temperate areas. Only Peripatopsidae occur in Australia, the family being represented by 31 genera and 71 species (Reid 1996). Elsewhere peripatopsids are found in southern Africa, New Guinea, New Zealand, and southern South America, clearly being Gondwanan in origin.

Onychophora are usually found in damp habitats, within rotting logs, under stones, in leaf litter and in soil. Inability to tolerate desiccation restricts them to moist microhabitats. However, some species are able to survive conditions of drought, also of severe cold, by going into torpor. Many are cryptic and, with their elongate, soft and extensible bodies, are able to penetrate cracks and crevices.

In Australia, most species are found along the Great Dividing Range in the east. Two species have been described from each of Western Australia, South Australia and the Australian Capital Territory, and 30 species occur in NSW, 17 in QLD and 20 in VIC. The greatest species richness occurs in the south-east of mainland Australia.

The conservative body form of Onychophora has made difficult the establishment of a higher level classification, and presently only the two family level taxa are recognised. A phylogenetic study by Reid (1996), based on morphological characters, supported an hypothesis of multiple origins for Australian Peripatopsidae. While the relationships between peripatopsids from different continents were well supported, relationships among most Australian genera were not well resolved. Chromosomal and molecular studies have revealed the presence of cryptic species and provided additional insights into peripatopsid relationships (Briscoe & Tait 1995; Gleeson et al. 1998; Rowell et al. 1995; Sunnucks & Wilson 1999).

Several new papers by Reid (2000a, 2000b) have been added to the database since it was first developed in 1999.

Acknowledgements

Mandy Reid is thanked for kindly checking the data entered in this section of the database, and for providing additional information.

Limital Area

Distribution data in the Directory is by political and geographic region descriptors and serves as a guide to the distribution of a taxon. For details of a taxon's distribution, the reader should consult the cited references (if any) at genus and species levels.

Australia is defined as including Lord Howe Is., Norfolk Is., Cocos (Keeling) Ils, Christmas Is., Ashmore and Cartier Ils, Macquarie Is., Australian Antarctic Territory, Heard and McDonald Ils, and the waters associated with these land areas of Australian political responsibility. Political areas include the adjacent waters.

Terrestrial geographical terms are based on the drainage systems of continental Australia, while marine terms are self explanatory except as follows: the boundary between the coastal and oceanic zones is the 200 m contour; the Arafura Sea extends from Cape York to 124 DEG E; and the boundary between the Tasman and Coral Seas is considered to be the latitude of Fraser Island, also regarded as the southern terminus of the Great Barrier Reef.

Distribution records, if any, outside of these areas are listed as extralimital. The distribution descriptors for each species are collated to genus level. Users are advised that extralimital distribution for some taxa may not be complete.

Diagnosis

Onychophora are soft-bodied, vermiform terrestrial invertebrates, with stumpy unjointed leg-like appendages or oncopods, paired antennae, eyes, a ventral mouth enclosing paired jaws, paired oral papillae with pores for the ejection of slime, and an integument composed of numerous, minutely scaled papillae, which give the animal its velvety appearance. Most are approximately 15 to 30 mm in length, but some attain about 150 mm length. Reproduction is gonochoristic (involving males and females), and oviparous, ovoviviparous or viviparous. Vivipary is not known to occur in any Australian species.