The Pycnogonida, or Pantopoda, is a small group of marine arthropods often referred to as sea spiders. The name sea spider is derived from the somewhat spider-like appearance of these animals.
Most pycnogonids are exclusively bottom dwellers, and they slowly crawl about with their long legs; some are able to swim, using vertical flapping movements of the legs.
Pycnogonids are mostly small animals with a body length ranging from 1 to 10 mm, but specimens of the deep sea, reach more than 5 cm in body length and have a leg span of more than half a meter.
Pycnogonids are carnivorous and feed on hydroids, soft corals, anemones, bryozoans and sponges. Some of the families present in the North Sea are characterised by the absence of one or both pairs of ancillary feeding appendages, the chelifores or palps, causing a considerable variation in the way of gathering the food. Pycnogonum littorale , without palps or chelifores, has been recorded with the tip of its proboscis embedded in the tissue of anemones, while in species with chelifores, the chelifores assist in bringing the food to the mouth so that there is no need to use the proboscis.