Before the present study, Plesionika rostricrescentis (Bate, 1888) and P. lophotes Chace, 1985 were the two Plesionika species unique in having a high basal rostral crest. A recently described species, P. erythrocyclus Chan & Crosnier, 1997 has a low basal rostral crest but is evidently related to P. rostricrescentis. Close examination of the abundant material collected during the MUSORSTOM expeditions and from Taiwan revealed that there are at least eight species in this ‘‘P. rostricrescentis-P. lophotes’’ species complex. These taxa are morphologically very similar but can be distinguished by their very distinctive colorations, which are often striking and consist of large circular spots. In the ‘‘P. rostricrescentis’’ group, which has the dorsal margin of the rostrum unarmed between the anteriormost tooth of the basal rostral crest and the subapical teeth, five species are recognized. Plesionika rostricrescentis is still known only by the holotype from the Kai Islands. Two new species, P. hsuehyui and P. suffusa, closely similar to P. rostricrescentis, are described. Plesionika hsuehyui is widely distributed from Taiwan to Fiji, while P. suffusa has only been found off New Caledonia. Plesionika erythrocyclus, previously known only from Taiwan and French Polynesia, occurs widely in the southern Pacific. Another new species, P. bimaculata, which closely resembles P. erythrocyclus, is distributed off New Caledonia and in adjacent areas. Three species are recognized in the ‘‘P. lophotes’’ group, which bear dorsal rostral teeth between the basal rostral crest and subapical teeth. Plesionika lophotes is restricted to the area between Japan and northwestern Australia. Two further closely similar new species, P. rufomaculata and P. scopifera are described, the former widely distributed from Okinawa to Futuna Island, the latter only off New Caledonia and Tonga. Although coloration is very important in distinguishing these species, species with similar color patterns do not necessarily belong to the same species group. Morphologically, these species are mainly separated by the height of the basal rostral crest, the number of rostral teeth, and the length of the stylocerite and the dactyli of the posterior three pereiopods. However, there is sexual dimorphism in the development of the basal rostral crest in these species, sometimes making positive identification of males and young specimens difficult. |
