![]() ![]() ![]() ![]() They lack a true exoskeleton, but the body is covered by a soft, chitinous cuticle. Like annelid worms, the Onychophorans have segmented bodies containing paired excretory organs (nephridia) and a combination of both male and female sex organs (monoecious). These mostly-tropical invertebrates, with only 75 extant species, live on the forest floor among moist, decaying leaves and feed on a mixed diet of plant and animal tissues. They decayed rapidly after death and were not well-preserved in the fossil record.Īt one time, the Onychophora or velvet worms were suggested as a possible evolutionary link (intermediate) between the annelids and the arthropods. ![]() But structural differences between the lateral appendages of polychaetes and early arthropods suggest that these two groups diverged from a common annelid ancestor some 500-600 million years ago. Some species may have had lobe-like lateral appendages similar to the parapodia of polychaete worms that thrive in the muddy sediments of today’s ocean floor. They had no distinct head capsule and lacked both eyes and antennae. These creatures were bilaterally symmetrical, soft-bodied, and multisegmented. A variety of marine worms (Annelida and Protoannelida) lived in the ocean sediments during the Cambrian period. ![]()
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