Biology/Natural History: Males have a pair of accessory (ovigerous) legs for carrying eggs. Females do not have these legs. This species seems to preferentially live on the giant green anemone Anthopleura xanthogrammica. Several individuals may occur on the same anemone (see below). It is one of the largest sea spiders to be found along our coast. The species feeds by jamming its proboscis into the anemone's tissues and sucking fluids. The proboscis has a wide aperture, probably to allow sucking up some particles in its food. Studies of closely related species have suggested that the animal has no heart (it probably pumps its blood by peristalsis).

Family Pycnogonidae is one pycnogonid family in which females lack ovigerous legs entirely. This is true for some other families as well, while in others the females have reduced ovigerous legs. Females release eggs from gonopores which are present on several legs near the base. The male, which is standing over or under her, fertilizes the eggs then gathers them up and sticks them to his ovigerous legs, where he cares for them. The eggs hatch as small protonymphon larvae which can swim. In a related closely related species to this one (P. litorale), the larva loses all three pairs of its larval legs and its proboscis at the fifth molt, then produces the adult proboscis and legs during later molts.