Pycnogonida

Small group of marine arthropods, treated generally as a class of Arthropoda. The class contains approximately 100 species in numerous families. Pycnogonids feed on anemones, corals, sponges, and bryozoans. The male carries the eggs and young larvae on his specialized front legs, called ovigers. He may fertilize eggs from more than one female and will carry them all. The gut and reproductive organs of the pycnogonid are contained not only in its body, but also extend to the tips of its leg.

The commonest species is Pycnogonum littorale, the common sea-spider, with four pairs of eight-jointed legs. It is found under stones at low water, and can sometimes be seen clinging to an anemone in a louselike fashion.

The largest form is Colossendeis gigas, which measures nearly 60 cm/24 in across, including its legs. This form is found only at great depths, as are the majority of pycnogonids, though some species extend to the foreshore.