Sea spider

Sea spiders are marine arthropods of the class Pycnogonida, hence they are also called pycnogonids (; named after Pycnogonum, the type genus; with the suffix -id). The class includes the only extant order Pantopoda (lit. 'all feet'), alongside a few fossil species which could trace back to the early or mid-Paleozoic. They are cosmopolitan, found in oceans around the world. The over 1,300 known species have leg spans ranging from 1 mm (0.04 in) to over 70 cm (2.3 ft). Most are toward the smaller end of this range in relatively shallow depths; however, they can grow to be quite large in the Antarctic region and in deep waters. Despite their name and slight resemblance, "sea spiders" are not spiders, nor even arachnids. While some literature around the 2000s suggests they may be a sister group to all other living arthropods, their traditional classification as a member of chelicerates alongside horseshoe crabs and arachnids has regained wide support in subsequent studies.