Pycnogonida

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Pycnogonida (Pantopoda; sea spiders; 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–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–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–ten pairs of legs, possibly as a result of polyploidy. Most pycnogonids are carnivorous and bottomdwellers, although some can swim. There are about 500 species found in all oceans, but more commonly in cold waters, and at all depths.