Onychophora (redirected from class Onychophora)

Onychophora (ŏn'əkŏf`ərə), small phylum with about 70 species of animals that are often called "missing links" between annelids (phylum Annelida) and arthropods (phylum Arthropoda). The thin cuticle and wormlike form of onychophorans are reminiscent of annelids, while the tracheal system and details of embryonic development foreshadow similar developments in arthropods. The unsegmented, stumpy legs with arthropodlike claws are unique. Onychophorans live inconspicuously in surface litter and under fallen logs, where humidity is high and protection against drying is greatest. Ancient onychophorans were marine. Modern species live in widely scattered wet, warm to temperate habitats in South Africa, Central America, and New Zealand, suggesting a much wider distribution of terrestrial forms in the past. The 10 genera are often referred to collectively as Peripatus.

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Onychophora [‚än·ə′käf·ə·rə]

(invertebrate zoology)

A phylum of wormlike animals that combine features of both the annelids and the arthropods.

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Onychophora

The only living animal phylum with true lobopods (annulate, saclike legs with internal musculature). There are about 70 known living species in two families, Peripatopsidae and Peripatidae. These terrestrial animals are frequently referred to as Peripatus. Onychophora comprise a single class or order of the same name. They were once considered a missing link between annelid worms and arthropods, but are best considered to be aligned with the arthropods.

They have a cylindrical body, 0.5–6 in. (1.4–15 cm) long, with one antennal pair, an anterior ventral mouth, and 14–43 pairs of stubby, unsegmented legs ending in walking pads and paired claws. Mandibles are present as modified tips of the first appendage pair. The body surface has a flexible chitinous cuticle. The body wall has three layers of smooth muscle, as in annelids, but the coelom is reduced to gonadal and nephridial cavities; the body cavity has an arthropodlike partitioned hemocoel; the heart is tubular with metameric ostia; and the nephridia are segmental. Gas exchange takes place by means of tracheae; spiracles are minute and numerous, located between skin folds. Slow locomotion is effected by legs and body contractions; the animals can squeeze into very tight spaces. The eyes, located at the antennal base, are the direct type with a chitinous lens and retinal layer. The sexes are separate; the testes and ovaries are paired; and the genital tracts open though the posterior ventral pore. Onychophora are oviparous, ovoviviparous, or viviparous.

The Onychophora are predatory, feeding on small invertebrates. They are largely nocturnal, occurring in humid habitats in forests.