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ZOOLOGY 13

ZOOLOGY 13. Marie Hecelle Antonette Q. Puso BS-BIO3A. ONYCHOPHORA. ONYCHOPORA. The  velvet worms  ( Onychophora  — literally "claw bearers", also known as  Protracheata )

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ZOOLOGY 13

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  1. ZOOLOGY 13 Marie HecelleAntonette Q. Puso BS-BIO3A

  2. ONYCHOPHORA

  3. ONYCHOPORA • The velvet worms (Onychophora — literally "claw bearers", also known as Protracheata) • are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs. • Currently there are around 10 genera and 110 species recognised within two extant families: the Peripatidae and the Peripatopsidae

  4. PHYSICAL CHARACTERISTICS: • The animals grow to between 0.5 and 20 cm (.25 to 8 in), with the average being about 5 cm (2  in), and have between 13 and 43 pairs of legs. • The body is caterpillar-like, encased in a thin chitinous cuticle. The anterior end is indicated by the antennae and by the ventrally directed mouth, while the posterior end, projecting behind the last pair of walking legs, bears the terminal anus.  • The body itself is not segemented except for the head, which is divided into three segments. • The first contains the two large antennae with an eye at the base . Some males also have other appendages believed to be involved in sperm transfer. • The second segment contains the jaw like mouth which is used for rasping into prey and then sucking out the nutrients. • The third segement holds the first pair of parapodia-like legs.

  5. Each of the legs bears a pair of chitinous claws for gripping, although on smooth substrate they walk on walking pads. • Unlike insect dermis, the cuticle of modern representatives is non-articulated, thin and soft and covered in hundreds of papillae and sensory hairs giving them a velvety texture, hence the common name ‘velvet worm.’  • The body wall consists of a non-cellular outer skin, the cuticula; a single layer of epidermis cells forming an internal skin; and beneath this, usually three layers of muscle, which are embedded in connective tissues.

  6. The body cavity is known as a "pseudocoel", or haemocoel. Unlike a true coelom, a pseudocoel is not fully enclosed by a cell layer derived from the embryonic mesoderm. A coelom is, however, formed around the gonads and the waste-eliminating nephridia. • Like insects the Onycophora breathe through spiracles. Spiracles open out to the enviroment and oxygen enters through a system of tubules (trachae) and is absorbed into the tissues across the moist surfaces. However, unlike the insects, onycophora have no control on the spiracles and they are always open, making the animal extremely vulnerable to dessication, so high levels of humidity are required.

  7. Contemporary Onycophorans are able to predate organisms several times larger than themselves by immobilising it with a gluey secretion from glands in its head, projected up to 30cm. The secretion holds the prey while the animal approaches it, bites through the cuticle, and injects a toxic, digestive saliva into the wound. • Both sexes possess pairs of gonads, opening via a channel called a gonoduct into a common genital opening, the gonopore, which is located on the rear ventral side. Both the gonads and the gonoduct are derived from true coelom tissue.

  8. In females, the two ovaries are joined in the middle and to the horizontal diaphragm.  • Males possess two separate testes, along with the corresponding sperm vesicle (the vesiculaseminalis) and exit channel (the vasaefferentia).  • Velvet worms are found in egg-laying (oviparous), egg-live-bearing (ovoviviparous) and live-bearing (viviparous) forms. • Velvet worms are sexually dimorphic, with the females being larger than the males.

  9. LIFE CYCLE • Fertilization may occur internally or externally, depending on the species. In the external case, the male deposits a spermatophore (sperm packet) onto the female's skin, where it is then absorbed into the body. The sperm then travels through the bloodstream to get to the ovaries. • Most velvet worms give birth to live young. The young either develop internally, being nourished via a placenta-like organ, or develop in eggs that hatch inside the female. Other species lay eggs which hatch outside of the female.

  10. Ex: pink velvet worm (Opisthopatusroseus) Tasmanipatusanophthalmus

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