Last year, specimens of live peripatus, Peripatoides novae-zealandiae, were sent from Victoria to the Chicago Museum of Natural History. Peripatus is an animal which most New Zealanders have probably seern at some time or another when they have kicked open a piece of rotting wood in the bush, but have not recognised as such, imagining it to be merely “another caterpillar.” The interest it holds for zoologists is reflected in this article written on the arrival of the New Zealand specimens at the Chicago Museum by Rupert L. Wenzel, assistant curator of insects, and published in the Chicago Natural History Museum Bulletin (July, 1949).

Billion-Year Ancestry?

These remarkable creatures belong to the Phylum Onychophora, an extremely ancient group that has existed for at least one-half billion years. A fossil form, Ashyeaia pedunculata (see figure 2), has been described from Middle Cambrian deposits of that age. The illustration shown is of a hypothetical reconstruction, but the actual fossil specimens show most of the details of the external structure rather clearly.

If the fossil described as Xenusion auerswaldi (see figure 2) actually represents an onychophoran or onychophoran-like animal, as it seems to, then the beginnings of the group might be extended back another one-half billion years, for Xenusion is from Proterozoic Algonkian rocks that are approximately a billion years old. Judging from the deposits in which these fossil forms were found, the early Onychophora were marine.

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The living species are terrestrial. They are few in number—about eighty species—and occur in the West Indies, Central and South America, South Africa, and the Indo-Australian region. Although they are terrestrial and have special breathing tubes known as “tracheae,” they are restricted to very moist environments; their thin skin makes them subject to very rapid dessication. They generally avoid light and live in rotten logs, under stones, under loose bark, etc., where they feed on small insects and other micro-organisms. Most of the species are small—about 2 to 3 inches long—but at least one attains a length of 5 inches.

One of the interesting protective adaptations of these animals is the ability to squirt a sticky, slime-like secretion that effectively tangles their enemies. The slime is secreted by long internal slime glands that extend almost the entire length of the body and is ejected from a pair of “oral papillae” (see figure 2), of which one is on each side of the head. Certain species can squirt the slime as far as twelve inches. Some Onychophora lay eggs. Others give birth to living young; in such species, special placenta-like structures may develop to facilitate the diffusion of nutrient materials through the uterine wall of the mother to the developing embryo, in much the same fashion as in mammals.

Worm-Arthropod Link

It is not only because of their great antiquity that the Onychophora excite the curiosity of the zoologist. An even greater fascination lies in the fact that these animals possess anatomical features both of the segmented worms (Annelida), of which the common earthworm is a familiar example, and the Arthropoda, the great phylum that contains the crabs, lobsters, shrimps, spiders, scorpions, millipedes, centipedes, and insects. The first peripatus described was considered to be a mollusc, and it was not until careful anatomical studies had been made that its position in the animal kingdom was appreciated. There can be little doubt that the arthropods evolved from worms or worm-like ancestors, and many zoologists consider that the Onychophora are an intermediate or linking group between the worms and the Arthropods. It is more probable, though, that the Onychophora represent an offshoot from the main line of evolution between the two.