"Every formula which expresses a law of nature
is a hymn of praise to God."

    Maria Mitchell (1818-1889)

    Astronomer

Virgin Islands onycophoran, Peripatus danicus. Virgin Islands National Park, Saint John, United States Virgin Islands.

A Touch of Velvet

PHYLUM ONYCHOPHORA: VELVET WORMS

    An unique phylum, in that it is the only one that does not include living aquatic forms.

    These strange and fascinating organisms are living fossils. Terrestrial forms almost identical to modern species date back to the Ordovician Period, but fossil marine precursors like Aysheaia are known from as far back as the Cambrian. Another species that is possibly belongs to this group is Xenusion, from the pre-Cambrian.

    The first individual ever described, from Saint Vincent in the Lesser Antilles, was at first classified as a mollusk, until it was realized that it didn't breath through gills, but with the use of tracheae. The 110 or so living species are distributed through the Antilles, South America, Africa, and Oceania.

    Apparently comprising an early offshoot of the lineage that gave rise to arthropods, onychophorans look like earthworms or caterpillars with tiny eyes, stubby legs and short antennae. Although possessing many pairs of legs (thus somewhat resembling centipedes), onycophores lack true external segmentation, unlike the more advanced arthropods. Unlike these last, their tracheae cannot shut close. This means that onycophorans loose water to the atmosphere very easily, and that means that they can only live in humid areas.

    Small predators of even smaller prey, they trap their victims with the use of a sticky fluid that hardens on contact with air, and which is discharged from pores in their heads. Then they dismember their meals with small but sharp, sickle-like jaws and suck their internal fluids. When attacked, some species secrete the same sticky substance (in this case also from pores along their bodies), which then entangles their would-be predators. Their pliable and soft integument have earned them the name of "velvet worms". Indeed, an onychophoran is so flexible that it is able to "filter" (there is no better word to describe it) through incredibly narrow spaces.

Onychophoran, Peripatus sp. Near Polo, Bahoruco Mountains, south-western Dominican Republic, Hispaniola.

This individual has secreted a sticky fluid through its mouth after being handled.

    In the Caribbean, they are found at least in the Greater and Lesser Antilles. These members of the family Peripatidae inhabit humid microhabitats under rocks and inside rotting wood, and only venture out at night. With very small eyes that can only distinguish between light and darkness, onycophores explore their surroundings with their long, retractile antennae that resemble those of a snail. One Jamaican genus lives only in dark caverns.

Virgin Islands onychophoran, Peripatus danicus. Virgin Islands National Park, Saint John, United States Virgin Islands.

Onychophoran, species undetermined, female. El Yunque National Forest, north-eastern Puerto Rico.

    For all their primitive traits, onychophorans have separate sexes, and are interesting in that they give birth to live offspring which are miniature replicas of the adults. Females are usually larger than males, but most species are still small animals. The largest are only about 20 centimeters in length.

Onychophoran, Peripatus juanensis. Guilarte State Forest, west-central Puerto Rico.

Looking like a cross between a slug and a caterpillar, onychophorans are among the most ancient living animals.