Class Pycnogonida of Phylum Arthropoda
Measures generally 3-4 mm; body chiefly made up of cephalothorax, abdomen being very small; generally four pairs of walking legs; long proboscis along with a mouth simple eyes, four in number; no excretory or respiratory organs. - These are generally known as sea spiders occur in all the seas. The narrow body is made up of a number of distinct segments. Prosoma (cephalothorax is the prominent region of the body and opisthosoma (abdomen) is much reduced. The head or cephalon bears four simple eyes mounted on the dorsal surface on a tubercle and a cylindrical proboscis. It as well bears a pair of comparatively small chelicerae and palps each. The trunk is formed of four cylindrical segments, of which the first one is fused along with the head. From each of the four segments, a pair of lateral processes project out to which the long walking legs are articulated. The legs are eight segmented and are generally much longer than the body. The abdomen appears as a short conical process.