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; phylum Arthropoda, subphylum Chelicerata)

A class of marine chelicerates, all of which are small (total body length usually 1–10 mm but up to 6 cm in some species, with a leg span of 75 cm). The narrow body comprises a cephalon and four to six distinct segments, the cephalon bearing a proboscis. The posterior part of the cephalon tapers to form a neck bearing four eyes mounted on a central tubercle on its dorsal surface. There is a pair of chelifores (possibly homologous to arachnid chelicerae), a pair of palps, and two pairs of ovigers (reduced in some species and absent in females of some species). The four to six pairs of eight-segmented walking legs articulate with large processes, pairs of which project from each segment, giving the animal the spider-like appearance to which its common name refers. Some species have eight to ten pairs of legs, possibly as a result of polyploidy. Most pycnogonids are carnivorous and bottom-dwellers, although some can swim. There are about 500 species found in all oceans, but more commonly in cold waters, and at all depths.

Subjects: Zoology and Animal Sciences.

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