Onychophora

Velvet worm rotated, mirror

Euperipatoides claw pair

Ooperipatellus viridimaculatus 34495501

Peripatopsis capensis internal anatomy IMG 0781a

Dissected Euperipatoides

Peripatopsis overbergiensis 45218773

Onychophora, commonly known as velvet worms, is a phylum of soft-bodied, many-legged invertebrates. The members of this phylum are characterized by their unique anatomical features, which include a velvety texture of the skin, caused by the presence of tiny papillae covered in a chitinous cuticle. Velvet worms are predominantly terrestrial organisms found in tropical and subtropical regions around the world, particularly in the Southern Hemisphere. They play a significant role in the ecosystem as predators of smaller invertebrates.

Anatomy and Physiology

The anatomy of Onychophora is distinguished by their elongated bodies, which can range from a few millimeters to over 20 centimeters in length, depending on the species. They possess a pair of antennae, multiple pairs of lobopod legs, and oral papillae that can eject a sticky slime used to capture prey. Internally, velvet worms have a simple digestive system, a closed circulatory system, and a pair of nephridia for excretion in each segment. Their respiration is facilitated through tracheae, a series of tubes that deliver oxygen directly to the tissues.

Habitat and Distribution

Onychophora are primarily found in moist, humid environments such as tropical rainforests, where they reside under logs, leaf litter, and debris. Their distribution is largely restricted to the Southern Hemisphere, with a significant number of species found in South America, Africa, Australia, and New Zealand. The requirement for high humidity levels limits their distribution and makes them susceptible to environmental changes.

Behavior and Ecology

Velvet worms are nocturnal predators, relying on their ability to produce a sticky slime to ensnare prey such as small insects and other invertebrates. This slime is projected from the oral papillae and can entangle prey from a distance. Once the prey is immobilized, the velvet worm uses its strong mandibles to feed. Their predatory behavior plays a crucial role in controlling the population of other invertebrates in their habitat.

Reproduction

Reproduction in Onychophora can be either sexual or asexual, depending on the species. Most velvet worms are oviparous, laying eggs that hatch into miniature versions of the adult. Some species exhibit ovoviviparity, where the eggs develop and hatch inside the female's body, and the young are born live. Parental care is observed in some species, with the female guarding the eggs until they hatch.

Evolution and Fossil Record

The fossil record of Onychophora is sparse, with the earliest known fossils dating back to the Cambrian period. This suggests that velvet worms have a long evolutionary history and may provide insights into the early evolution of arthropods. Their unique anatomical features place them in a key position in the study of the evolution of more complex invertebrates.

Conservation

The conservation status of many Onychophora species is of concern due to habitat destruction, climate change, and pollution. Their dependence on humid environments makes them particularly vulnerable to changes in climate and habitat fragmentation. Conservation efforts are necessary to protect these unique organisms and their habitats.