Early relative of velvet worms had a spiky side

Today’s 180 or so species of velvet worms all look and act pretty much the same: These soft-bodied creatures live in dark, moist environments; they spit slime to immobilize their prey; and most segments of their bodies have stubby, jointless legs tipped with retractable claws. But fossils unearthed in southern China reveal that about 500 million years ago, one of these creatures’ earliest known relatives (artist’s concept, above) looked like a thorny, long-legged caterpillar. Named Collinsium ciliosum, or “Collins’ hairy monster,” after the Canadian paleontologist who discovered and first drew its fossils, the 8.5-centimeter-long worm had 15 segments and lived on the sea floor. Each of the legs on its first six body segments were fringed with fine, hairlike structures, whereas those on the nine hindmost body segments were tipped with one large claw apiece, the researchers report online today in the Proceedings of the National Academy of Sciences. Because claws wouldn’t have been useful for walking on a muddy seafloor, the team suggests that the worm clambered up on firm objects such as rocks or sponges and then extended its first six pairs of legs into the water flowing by, filtering the currents for its food. Exposed to predators in such a position, Collinsium would have benefitted from the dozens of spikes lining its back, the tallest of which ranged between 6 and 12 millimeters long. The protective structures must have been made of minerals produced by the worms, the researchers say: Whereas the bodies were preserved in a squished-flat arrangement, the spines were preserved in their original 3D shapes.