of rainy warm weather. Put a tist-sized clump of 

 damp moss into a pint bottle half full of water, shake 

 vigorously for five minutes, remove the moss, strain 

 the water through a pocket handkerchief, and exam- 

 ine the residue on the cloth with a strong lens or a 

 low-power microscope. Nearly every clump of moss 

 in the world is home to a few bear animalcules. But 

 they are minute creatures — rarely more than i/o-, 

 of an inch in length. 



The name "tardigrade" refers to the slow steps 

 taken by the bear animalcule as it lifts its stout body 

 along on four pairs of stubby legs. Three legs arise 

 on each side, and a fourth is at the posterior end. All 

 legs end in a little cluster of four or five claws or 

 hooks that are movable and help the animal cling to 

 a moss plant, a lichen, a bit of bark, or a shingle on 

 the roof. A tiny eyespot adorns each side of the body 

 just forward of and higher than the first pair of legs. 



Bear animalcules are scavengers, feeding on both 

 animal and plant matter sucked into the small mouth 

 or cut free through use of a pair of sharp teeth. Each 

 individual combines the organs of both sexes, but the 

 feature most effective in insuring the continuation of 

 bear animalcules in the world is their ability to lose a 

 little water, become dormant, and be blown in the in- 

 active state as dust particles. As a result, most tardi- 

 grades are cosmopolitan and can be collected as eas- 

 ily in the arctic as in the tropics, in Africa, America, 

 Eurasia, or Australia. 



Tardigrades can remain dormant for years, and 

 then become active again in a few minutes when 

 wet or exposed to very humid air. It is after rains that 

 they climb about and can be shaken free from a sup- 

 port. Some bear animalcules inhabit ponds, particu- 

 larly temporary pools. A few are marine, and creep 

 in the capillary water film between sand grains on 

 the beach, or cling to the surface of sea cucumbers, 

 sea fans, and other slow-moving or attached animals. 



Bear animalcules are so uncomplicated anatomi- 

 cally that biologists have often been uncertain of 

 their proper place in the animal kingdom. Sometimes 

 the tardigrades have been simply left in a little phy- 

 lum of their own, sometimes grouped with nematode 

 worms in the phylum Aschelminthes. 



The Velvet Worms 



( Class Onychophora ) 



Almost 150 years ago, the Reverend Landsdowne 

 Guilding was poking about, searching for snail shells 

 on the hilly slopes of the island of St. Vincent in the 

 West Indies. Under a rotting log he found an inch- 

 long brown animal. It moved slowly, and he mistook 

 it for a slug. Since it did not have a shell he popped it 

 into a vial of preservative solution, and did not ex- 

 amine it carefully until many months later. In 1825 

 he described the strange animal for science as a mol- 



The head end of a peiipatiis, shown in color plate 

 88, here greatly enlarged. Thou.sands of minnte papil- 

 lae give the skin of a peripatus its unique velvety tex- 

 ture. (Panama. Ralph Buchsbaum) 



lusk, Liiuax jiilifonnis. curiously equipped with a 

 series of lumps along each side of the almost cylin- 

 drical body as though it were a centipede. That the 

 "lumps" were really legs never occurred to him. 



Not until many years later did anyone examine a 

 living velvet worm and realize how neatly it handles 

 its more than two dozen pairs of stubby legs. Each 

 leg ends in a flexible knob armed with a pair of claws. 

 From these the name of the class Onychophora 

 ("claw-bearing") is derived. On its unusual legs the 

 creature (Plate 88) glides over the ground, latching 

 each leg temporarily to some support by expert move- 

 ment of the claw-bearing knob. 



A pair of projections at the head end, which the 

 Reverend Mr. Guilding mistook for the tentacles of 

 a slug, are actually flexible antennae. They bear no 

 eyes and curl out of harm's way, whereas the tenta- 

 cles of a land snail or slug carry eyes and draw back 

 inside the head like an inverted glove finger. Velvet 

 worms do have a pair of simple eyes, one on each 

 side of the head. But these organs are more like those 

 of some polychaete worms than of any mollusk. 



The West Indian velvet worm was eventually rec- 

 ognized as a creature that superficially resembled a 

 caterpillar but was not an insect. It was neither a 

 centipede nor a millipede. It had many features in 

 common with annelid worms, yet was no annelid. It 

 was a "walking worm," and so it received the generic 

 name Peripatus. 



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