Sea Spider

Long-legged spiderlike marine animal usually living near the shore, walking about on the bottom of the ocean on spindly legs or crawling among marine plants and animal colonies. Some sea spiders embed themselves in shellfish. The 600 widely distributed species vary in size from 2 mm in tropical shallow-water types crawling about over the surface of sessile animal colonies or seaweeds, to more than 50 cm (more than 20 in) in some deep-sea forms. Their unusual body form makes their relationships to other arthropods obscure.

Typically, the sea spider head has two pairs of simple eyes, a very long tubular proboscis, and three pairs of appendages. The proboscis sucks in the juices of hydroids or other soft-bodied sea animals. The first pair of appendages holds food and cleans the mouth, which is a small opening at the end of the proboscis. The second pair of appendages has leglike functions. The third pair is specialized in the male to carry egg masses, which it takes from the female and cares for until they hatch. Four pairs of walking legs follow, but sometimes additional pairs are found. The elongated trunk of the sea spider has four segments, each with a pair of long, jointed legs. The abdominal segment, sometimes fused with the head, is little more than an alimentary canal. The sex organs are in the legs, from which the egg masses pass through slits.

Scientific classification: Sea spiders belong to the class Pycnogonida in the phylum Arthropoda.