Some New Zealand Parasitic Copepoda of the Family Anthosomidae
The material on hand agrees well with Thomson's description and figures (1889, p.366-7, pl. 27, figs. 2a-j); this could be expected in the case of the Otago Museum material since it had been identified as L. percis by Thomson himself.
Wilson (1936, p.340) claimed to have found this species on Promicrops itaira at the Dry Tortugas. The only description he gives is that the first antennae "prove to be six-segmented, with no setae except two minute ones at the tip of the end segment". Since in A. percis the antenna is seven segmented with setae on every segment it seems that Wilson's record is of yet another species of Aethon.
A. percis resembles A. quadratus Krøyer in its general form and in its possession of forked, unsegmented, second pereiopods, and in the development of the third pereiopods, but it can be separated from A. quadratus in that the latter has the posterior lateral lobe of the cephalothorax extending out well beyond the anterior (which may even be missing; Krøyer does not make this clear) while in A. percis the posterior lobe is only slightly longer than the anterior. Further, A. quadratus has a well developed neck region, almost entirely missing in A. percis.