To date, only a couple of hundred species of onychophorans are known, but it is very likely that many more remain to be discovered and described. They fall into two family groups, the Peripatidae and the Peripatopsidae. The peripatids inhabit tropical America, and have also been found in tropical western Africa and south-eastern Asia. Peripatopsids are found in countries associated with the previously connected so uthern super-continent, Gondwanaland, such as Chile, South Africa, Australia, New Guinea and New Zealand. Of these, Australia is richly endowed with the greatest number and diversity of onychophorans, with 74 described species (compared with three species from South America, nine from South Africa, and eight each from New Zealand and New Guinea).

 

Habitat : 

 

In Australia, velvet worms can be found in regions as diverse as sub-alpine south-eastern Australia, the wet tropics, and the forests of south-western Western Australia. Most species are found in relatively moist coastal areas, including tropical and temperate rainforest as well as eucalypt forests and woodlands with pockets of remnant wet forest. These habitats have become fragmented by past climatic changes and, more recently, by human disturbance.

 

They live in moist places, such as rotting logs and leaf litter.

 

Feeding and Diet

 

Despite their apparently gentle appearance, velvet worms are voracious and active carnivores, feasting on other small invertebrates (for example, termites, woodlice and small spiders) that they encounter during their travels.

 

Velvet worms capture their prey by squirting sticky slime from their oral tubes. The slime effectively entangles the prey so it can't escape. The velvet worm bites off parts of the prey then sucks them up after they have been softened by digestive saliva extruded from the velvet worm's mouth. Any undigested portions are excreted by the anus at the rear end of the body. Segmental excretory organs (the nephridia) also remove metabolic wastes.

 

The slime is also squirted in self-defence. An enemy with a face full of slime gives the velvet worm time to escape.

 

Other behaviours and adaptations

 

Velvet worms are quite secretive and display 'photonegative' behaviour, meaning they hide away from light.

 

Velvet worms breathe through little holes called 'trachea' that are scattered over the body. These pores are permanently open, so water from the body can easily be lost. The porous nature of their cuticle means that velvet worms can easily dry out, so they are restricted to areas of high humidity, such as in logs, under stones, in the soil, or among leaf litter.

 

 

Life cycle

 

Reproduction takes place in an extremely curious manner. The male deposits packets of sperm (spermatophores) on the body of the female, for example on her back or sides. Some species deposit their spermatophores directly into the genital opening of the female. This method has been observed in a few Australian species. In those species that deposit sperm on the skin of a female, the skin tissue collapses where the sperm are deposited and the sperm migrate into the female's body, where they penetrate the ovaries to fertilise the eggs. Many species have a pair of sperm receptacles close to the ovaries, and these can be used to store sperm for many months to fertilise eggs as needed. This is a useful adaptation when encounters between males and females may occur only rarely. The males of most species have glands on the underside of the legs that secrete a pheromone to attract females.

 

Embryonic development is unusually diverse in onychophorans. Some species lay large yolk-filled eggs, while others retain yolky eggs within the female until they are ready to hatch. Some other species (though none of the Australian species) have small eggs without a yolky food source, and the developing young obtain nourishment from their mother's body in a manner similar to placental mammals. In all cases, the young are fully developed when born, and, apart from lacking complete pigmentation, look like miniature adults.

 

Mating and reproduction

 

In a number of Australian species, the males place their spermatophores on their heads like tiny trophies in readiness to present them to a female. Some species have developed elaborate structures, including spikes, spines, hollow stylets, pits, and depressions to either hold the sperm, or assist its transfer to the female. These structures may also have a role in species recognition, in a fashion similar to the often elaborate genital structures of insects (but this is not known for certain). Two species, Florelliceps stutchburyae and Planipapillus annae, have been observed mating. In both species, the head of the male holding a package of spermatophores was placed against the genital opening of the female at the rear end of her body and the spermatophores were transferred directly into her genital opening.

 

Classification

 

Phylum  :  Onychophora

Kingdom  : Animalia