Velvet worms are ecdysozoan invertebrate animals of the phylum Onychophora (from Greek, onyches, "claws"; and pherein, "to carry") with approximately 200 species. These elongate, obscurely segmented organisms have tiny eyes, antennae, many pairs of legs, and slime glands. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. Most common in tropical regions of the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting an adhesive mucus. The two extant families of velvet worms are Peripatidae and Peripatopsidae. They show a peculiar distribution, with the peripatids being predominantly equatorial and tropical, while the peripatopsids are all found in what used to be Gondwana.
Formerly considered part of Tracheata, velvet worms are now considered close relatives of the Arthropoda and Tardigrada, with which they form the taxon Panarthropoda. This makes them of palaeontological interest, as they can help reconstruct the ancestral arthropod. In modern zoology, they are particularly renowned for their curious matingbehaviour and for bearing live young.
Species of Onychophora from Denmark
Global range of Onychophora: Peripatidae in green, Peripatopsidae in red, and fossils in black
The Slimy, Deadly Velvet Worm
Velvet worm :
courtesy to : www.australianmuseum.net.au/velvet-worm
While the body structure of onychophorans is a very simple one, it works well. It has enabled them to live very successfully on land, largely unchanged in structure, for about 500 million years. Although first mistakenly described in 1826 as a type of slug, the evolutionary history of onychophorans has long fascinated scientists. They have been described as a missing link between the arthropods (a group that includes insects and spiders) and the annelids, or segmented worms (which includes earthworms and beach worms). It is now known that onychophorans are much more closely related to arthropods than to annelids.
Photographer: Stuart Humphreys © Australian Museum
Velvet worms belong to a phylum of their own, the Onychophora, meaning 'claw-bearers'. They are small, terrestrial (land-dwelling) worms that look rather like caterpillars, with antennae and clawed legs down the whole length of their bodies.
Velvet worms range up to about 10 cm in length, but those most often encountered in Australia are between two and four centimetres long. Apart from a few white cave-dwelling species, they are generally blue-grey or brownish in colour, often intricately and beautifully patterned, with stripes, diamonds, spots or chevrons. The body is covered by a very thin layer of chitin and the skin is covered with numerous papillae and close-set ring-like markings. The papillae, comprised of delicate rows of overlapping scales, give onychophorans their velvety appearance (explaining their common name). They make the skin hydrophobic, or water repelling. This is a useful trait to keep the skin dry when inhabiting moist environments. The papillae also have at their tips tiny hairs that are sensitive to touch and smell.
Australian velvet worms have between 14 and 16 pairs of lobe-like, stumpy legs, although species from other parts of the world may have up to 43 pairs of legs. Their characteristic flowing movement is caused by the alteration of fluid pressure in the limbs as they extend and contract along the body. This movement led to a second common name, peripatus, from 'peripatetic', which means 'wandering'.
Velvet worms also have two conspicuous antennae on the head, and, behind these, two simple-lensed eyes and a pair of modified legs, called 'oral tubes'. These are used to assist in prey capture. The paired, toothed, sickle-shaped jaws sit in the middle of a rounded, fleshy pad on the underside of the head.
Body Length 2 cm -10 cm
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).
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.
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.
Phylum : Onychophora
Kingdom : Animalia
Reid, A. L. 1996. A review of the Peripatopsidae (Onychophora) in Australia, with descriptions of new genera and species, and comments on Peripatopsid relationships. Invertebrate Taxonomy10(4): 663-936.
Storch, V. and Ruhberg, H. 1993. Onychophora. In Microscopic Anatomy of Invertebrates: Treatise Vol. 12, Onychophora, Chilopoda and Lesser Protostomata. (Eds F. W. Harrison and M. E. Rice.) Pp. 11-56. (Wiley-Liss, Inc., New York.).
Sunnucks, P. and Tait, N. 2001. Tales of the unexpected. Nature Australia Winter 2001, 27(1): 60-69.
Common name: velvet worms
Onychophorans are soft-bodied, worm-like invertebrates that have been considered an intermediate link between annelids and arthropods, although it appears they are more closely related to arthropods. Their worm-like body is not obviously segmented like annelids. However, their head is composed of three segments with a pair of antennae and usually a pair of eyes on the first segment along with a pair of ducts, called oral papillae, that secrete a sticky substance which dries on contact with air and is used for prey capture and to deter predators. The second head segment has a mouth with paired, toothed, sickle-shaped jaws. Unlike arthropods, onychophorans do not have a stiff exoskeleton. Their thin, flexible cuticle is covered in minute tubercles that give them a velvety appearance and their common name - velvet worms. The tubercles are also sensory and detect vibrations and scents. Onychophorans have many pairs of lobe-like, unsegmented, stumpy legs (14-16 pairs in Australian species and up to 43 pairs in some overseas species), which have a series of pads towards the end and a pair of claws at the tip. Their tracheae are always open and as a result they require a humid environment to avoid desiccation. They range in size from about 2-10 cm in length, and are generally blue-grey or brownish in colour, often intricately patterned with stripes or spots.
Distribution and diversity:
Onychophorans occur largely along the wet eastern and south-eastern margin of the continent, but four species are also recorded south-western Western Australia. The group is undisputedly Gondwanan in origin, with two families and about 165 species described mainly from the southern hemisphere, while in the northern hemisphere they are only found in tropical and subtropical regions. There are currently 71 described species from Australia in 31 genera accommodated in one family (Peripatopsidae), with most species having been recognized within the last 10-15 years. However, there are many undescribed taxa and the true size of the Australian fauna has been estimated at 250 species.
Life cycle :
In many onychophorans, the male indiscriminately attaches a spermatophore (sperm packet) to the body of the female. The tissue beneath the spermatophore dissolves and the sperm travel through the female’s body to the ovaries where they fertilse the eggs. Alternately, the males of some species deposit their spermatophores directly into the genital opening of the female. In several species, the males place their spermatophores on their heads, ready to present them to a female. Some have developed elaborate structures, including spikes, spines, hollow stylets, pits, and depressions to hold the sperm and/or assist its transfer to the female. Onychophorans either lay large yolk-filled eggs into the soil and leaf litter or retain the eggs within the female and the young are born live. Immature onychophorans look like miniature adults with reduced pigmentation and go through several moults before adulthood.
Although slow moving, onychophorans are active nocturnal predators that feed on a wide variety of small ground-dwelling invertebrates. They are able to capture prey several times their own size and up to 30 cm away with a sticky substance that they eject from the oral papillae in their head. Once immobilised, onychophorans use their jaws to break through the prey’s cuticle and secrete digestive saliva onto the exposed flesh which is then sucked up into the mouth.
In Australia, onychophorans occur in eucalypt forests and woodlands, tropical and temperate rainforest, moist coastal areas and sub-alpine regions. To avoid desiccation they are restricted to damp microhabitats and can be found within rotting logs, under stones, in leaf litter and soil, and in caves. However, some species are able to survive drought and severe cold by going into torpor. When present, their predatory impact is likely to be significant; however, their effect on ground-dwelling invertebrate communities is largely unknown.
The Creature Feature: 10 Fun Facts About Velvet Worms
Photo: Peripatoides novazealandiae by Frupus, via Flickr. Distributed under a CC-BY-NC-2.0 license.
VELVET WORMS, OTHERWISE known as Onychophora, are reclusive little animals that have changed very little in the last 500 million years.
Scientists have described some 180 modern species. They can be found in moist, dark places all around the tropics and Australia and New Zealand. Smaller species are less than an inch long, while the largest reach lengths of about 8 inches.
They come in a dazzling array of colors and exhibit some pretty weird and complex behaviors. I’m sure you’ll be just as charmed by them as I am.
1. Velvet worms have hydrostatic skeletons. Velvet worms don’t have hard exoskeletons like arthropods. Instead, their fluid-filled body cavities are covered in a thin skin and kept rigid by their pressurized internal liquids. They move by the alteration of fluid pressure in the limbs as they extend and contract along the body.
2. They have velvety, water-proof skin. Their entire bodies are covered with papillae, tiny protrusions with bristles sensitive to touch and smell. The papillae are made up of overlapping scales, which gives the velvet worm its velvety appearance. It also makes their skin water-repellant.
Photo: Euperipatoides rowelli by Andra Keszei, via Flickr. Distributed under a CC BY-NC-SA 2.0 license.
3. They have lots of little stubby feet. Their feet are described as conical, baggy appendages. Depending on the species, a velvet worm can have between 13 and 43 pairs of feet. The feet are hollow, fluid-filled, and have no joints.
4. Each little stubby foot has a claw. Each foot is outfitted with a hooked claw made of chitin (lending the group its scientific name, Onychophora(‘Claw-Bearers’)). Velvet worms use their claws when walking on uneven terrain; on smoother surfaces, they retract their claws and walk on the foot cushions at the base of the claws.
5. Velvet worms are vulnerable to dehydration. Like insects, velvet worms breathe through holes along their bodies called tracheae. Unlike insects, velvet worms cannot close these holes to prevent water loss, so they easily dry out. For this reason, velvet worms spend most of their time hidden in moist areas in the soil, under rocks, and in rotting logs. They’re most active at night and during rainy weather.
6. They use slime as a weapon. Velvet worms are ambush predators, hunting other small invertebrates by night. To subdue their prey, they squirt a sticky, quick-hardening slime from a pair of glands on their heads. After the prey is ensnared, the velvet worm bites into it, injecting digestive saliva that helps liquefy the insides for easier snacking. The slime is energetically costly to make, so velvet worms will often eat any excess slime they have produced to shore up their reserves. Check out a sliming in action here.
7. At least one species is highly social with a strict dominance hierarchy. Euperipatoides rowellilive in groups of up to 15 individuals, ruled over by a dominant female. The group hunts together, and after a kill the dominant female always feeds first, followed by the other females, then the males, and finally the young. The social hierarchy is established and maintained through aggression: higher-ranking individuals will chase, bite, kick, and crawl over subordinates.
Photo: Euperipatoides leuckartii by Michael Whitehead, via Flickr. Distributed under a CC BY-NC-SA 2.0 license.
8. Velvet worms are survivors. They belong to a clade that has been around for over 500 million years. Fossilized marine versions of velvet worms from the Cambrian period have been found in the Burgess Shale in Canada (505 million years old) and the Chengjiang formation in China (520 million years old). Velvet worms are now considered to be close relatives of arthropods and tardigrades. They’re of interest to paleontologists because they might help provide an idea of what the ancestors of arthropods were like.
9. They have a number of bizarre reproductive strategies. All the velvet worms reproduce sexually, except for Epiperipatus imthurni (they reproduce by parthenogenesisand no males have ever been observed).
The other velvet worm species have evolved several creative ways to deliver the male’s sperm to the female’s egg. Some species deposit their spermatophores directly into the female’s genital opening, though the means by which they do this varies. In some species the male uses special structures on his head; other species have spikes, spines,or pits to either hold their sperm or transfer it to the female.
The males in the genus Peripatopsis just deposit their spermatophore on seemingly random spots on the female’s body. This stimulates a localized breakdown of her skin so the sperm can pass into her body and migrate to her ovaries, where fertilization takes place.
10. Most velvet worms give birth to live young. Female velvet worms can store sperm for many months before using them to fertilize their eggs. Their gestation period can last up to 15 months in some species. Most give birth to live young, although a few species lay eggs. Young velvet worms are born fully developed and looking like miniature versions of the adults.
Some Videos :
Velvet Worm (Onychophore)
Panamanian Velvet Worm
Velvet Worms (Peripatus)
Recommended websites :
KEEPING YOUR VELVET WORMS
Velvet worms main requirement is a dark and damp place, where they can spend the days motionless and come out to hunt at night. Their prey is small invertebrates and small mollusks. They shoot an adhesive liquid from a receptacle located near their mouth, when this adhesive dries, after few seconds, the prey gets stuck to the ground and cannot escape,the velvet worm then approaches its prey with its mandibles and pokes a hole in the prey and secretes digestives juices, finally it applies its mouth to the wound and sucks out the food from the victim. This “sticky glue” is also used as a defense against their own predators.
TEMPERATURE The ideal conditions for the velvet worms is cool room temperature with a regular fine water spray in the cage, keeping the cage damp at all times. It is essential that the water used is rain water as they cannot tolerate any chemicals on their skin.
SUBSTRATE Any soil based substrate can be used like, Coir (coconut husk), vermiculite or even garden soil.Keep this substrate slightly moist by spraying (very lightly) with water and place wood, bark and moss on the surface for hiding places. The Water used should be rain water.
We find tupperware style boxes serve well as cages with only minimal ventilation added.