Onychophorans

Onychophora. Spanish and Portuguese: Onicoforos.

These moderate-sized (BL 2—5 cm), caterpillarlike terrestrial animals, neither Anne lida nor Arthropoda, form a separate phylum but combine qualities of both groups (Marcus 1937). Their annelid characteristics include internally repetitious body segmentation, an eye with a simple lens, the presence of nephridia (kidneylike organs) in most body segments, and a soft, flexible, wormlike shape, lacking a hardened exo-skeleton. Some of their arthropod features are an open body cavity and circulatory system, modification of a pair of appendages into mandibles, claws on the appendages, a breathing system of tracheae, and an elongate dorsal heart. They also grow by shedding their skins like arthropods.

Onychophorans have their own special structures, including a transversely wrinkled and well-pigmented integument, each fold with many regularly placed papillae. They also have a pair of annulate antennae and special glands in the mouth cavity used to shoot streams of slime to capture prey and fend off enemies.

Knowledge of the biology of these creatures is scant. They require moisture and survive only in humid tropical environments or damp microhabitats in temperate regions. Here they inhabit leaf litter, rotten wood, and other moist retreats, such as banana stems (Young 1980) and cavities under bark. If agitated, they face their antagonist and forcefully spurt streams of sticky mucus from the slime glands in the mouth. These solidify into sticky threads that entangle anything they touch, producing a noxious mess. Silk shooting is also used to immobilize prey.

These are nocturnal animals. Their food

Figure 4.1 ARTHROPODS, (a) Onychophoran (Macroperipatus torquatus, Peripatidae). (b) Sea "roach" (Ligia exotica, Ligiidae). (c) Pillbug (Armadillidium vulgare, Armadillidiidae). (d) Sow bug (,Porcellio laevis, Porcellionidae). (e) Sand "flea" (Orchestia platensis, Talitridae).

probably consists mainly of other small invertebrates or of partially decomposed leaf and wood tissue. One species is known to invade termite galleries in rotting wood to prey on their owners (Janvier 1975).

In the New World tropics, there are eight genera of Onychophora, including fifty-seven species in two families (Peck 1975). Metaperipatus (Peripatopsidae) live in damp forests in southern Chile (Claude-Joseph 1928). The various genera of Peripatidae are much more widespread in the rain forests of Amazonia and Central America (to southern Mexico) and the Caribbean. Here they crawl over and among the litter in search of other small invertebrates (termites, caterpillars, snails, etc.) on which they prey. Peripatus heloisae has been found in large numbers in ground-nesting termite mounds in Brazil by Carvalho (1942), who believes them to be termitophagous. Spele-operipatus speloeus is a blind and pale species found in caves in Jamaica (Peck 1975). The largest species, which measures up to 15 centimeters in length and lives in Trinidad, is the collared peripatus (Macroperipatus torquatus; fig. 4.1a) so named because of bright yellow markings around the bases of the antennae (Ghiselin 1985).

References

Claude-Joseph, F. 1928. Observations sur un

II: 285-298. Ghiselin, M. T. 1985. A movable feaster. Nat.

Janvier, H. 1975. Un peripate du Chili chasseur de termites. Entomologiste 31: 63-68.

Leitäo de Carvalho, A. 1942. Sobre "Peripatus heloisae," do Brasil Central. Mus. Nac. Rio de Janeiro (n.s.) Zool. Bol. 2: 57-73.

Marcus, E. 1937. Sobre os Onychophoros. Insto. Biol. Sec. Agric. Säo Paulo Arch. 8: 255-266.

Peck, S. B. 1975. A review of the New World Onychophora with the description of a new cavernicolous genus and species from Jamaica. Psyche 82: 341-358.

Young, A. M. 1980. On the patchy distribution of onychophorans in two cacao plantations in northeastern Costa Rica. Brenesia 17: 143-148.

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