Oculophryxus bicaulis, a new genus and species of dajid isopod parasitic on the euphausiid Stylocheiron affine Hansen.

A new genus and species of dajid isopod is described from the euphausiid Stylocheiron affine Hansen. The isopod is a member of the Dajidae Krøyer, 1842, which are ectoparasites of shrimp, mysids, and krill. The female of the new genus and species is unique in its attachment to the eyestalk of its euphausiid host. The well-developed antennae encircle the eye peduncles of the host. The parasite presumably feeds by sucking blood directly from the head of the euphausiid. The new genus can be distinguished from other genera by the elongate, spoon-shaped antennae, the number of pereopods, and the indistinct abdomen. The male parasite attaches to the posterior of the female near the margin of the marsupium. The male can be distinguished from other genera by the rudimentary 7th pereopod. Epicaridia, microniscus and cryptoniscus larvae were not observed. The parasite was found in samples taken during 7 oceanographic surveys made along the west coast of Baja California. The parasite was found on the furciliae, juveniles, and immature males and females of S. affine. Female isopods may castrate their hosts as none of the infected hosts (n = 27) had reached maturity. Of the 3 eco-phenotypes of S. affine that are found in the region, the isopod apparently prefers the California Current morph. However, in the Gulf of Mexico, a similar parasite was found on S. longicorne Sars.