Pinnotheres nudus Holmes, 1895

Campos, Ernesto, 2016, The Pinnotheridae of the northeastern Pacific (Alaska to Mexico): zoogeographical remarks and new bivalve hosts (Crustacea, Brachyura, Pinnotheridae), Zootaxa 4170 (2), pp. 311-329 : 323

Pinnotheres nudus Holmes, 1895

( Figs. 4 E–H)

Diagnosis. Carapace slightly broader than long, subquadrate to orbicular in outline, convex, curving downwards towards margins, surface smooth, naked, regions not defined. Front deflexed, rounded, not protruding, central portion continued downward as triangular process between antennules, smaller triangular processes at sides partly separating orbits from antennular fossettes. Orbits ovate, wide inner hiatus partly filled by base of antennas; eye peduncles very short, stout, cornea minute. Antennules oblique; antennular fossettes communicate each other beneath front. Third maxillipeds oblique, nearly fitting buccal area; merus broad, smooth, subquadrate, outer margin produced into broadly rounded laminate expansion; propodus oblong, distally rounded; dactylus spatulate, articulated near base, extending somewhat beyond propodus. Chelipeds moderate, smooth, naked; hands narrow, rather thick, widest immediately behind articulation of dactyl; fingers nearly or quite as long as palm, subconical, not conspicuously dentate on inner margins, partly covered by very short, dense pubescence. Pereiopods 2-4 subequal, pereiopod 5 smaller, all smooth, little compressed, dactyli acute, nearly straight, those pereiopod 5 longer, more slender than preceding pairs. Abdomen of female nearly circular in outline, covers entire sternal surface; six somites and telson separated, fourth, fifth and sixth being subequal, larger than others (modified from Holmes, 1895).

Distribution. Santa Cruz (type locality), Monterey, California, U.S.A. (Holmes 1895, 1900).

Hosts. Unknown.

Remarks. Pinnotheres nudus is known by its original description based on two syntype females collected at Santa Cruz , California, U.S.A. The two syntypes deposited in the California Academy of Sciences were destroyed in the San Francisco fire after the earthquake of April 18, 1906 . Measurements of the syntypes given by Holmes (1895) (cl 20 mm, cw 24 mm; cl 15.5 mm, cw 19 mm). For more than a century there have been no new published records for this species. Campos & Manning (2000) nevertheless suggested that P. nudus should be placed in synonymy with Opisthopus transversus . Both species share several features including a large antenna, visible dorsally ( Fig 4A , E), a third maxilliped with a carpus that is shorter than the spatulate propodus, and a spoonshaped dactylus that is inserted proximally on the ventral margin of the propodus, with its apex extending beyond the tip of this article ( Fig. 4D , H). Both species possess pereiopods 2–4 that are subequal in length and shape, whereas the pereiopods 5 are the shortest. Furthermore , the abdomen ( Fig 4B , E) is nearly circular, composed of six somites and a freely articulating telson, with somites 4–6 subequal and larger than the others. Although these shared features may suggest that both species are synonymous, a reappraisal of their morphology showed some important features that were overlooked by Campos & Manning (2000). Pinnotheres nudus has a front that is deflexed, rounded, not protruding ( Fig. 4 E), the central portion continued downward as a triangular process between the antennules; the subconical fingers of the chela are not conspicuously dentate along the inner margins, and although described as long as the palm, the original figure shows that both pollex and dactylus are longer than the palm ( Fig. 4 G), and the dactyli of pereiopods 2–4 are acute, nearly straight whereas those of pereiopods 5 are relatively longer and more slender than in the preceding pairs. In contrast, O. transversus has a slightly produced, deflexed, almost straight, emarginate front ( Fig. 4A ); the fingers of the chela are shorter than the palm and the cutting edge of the fingers has one small tooth at the base of dactylus and two or three at base of the pollex ( Fig. 4C ), and the dactyli of pereiopods 2–4 are uniformly curved and small, whereas the dactyli of the pereiopods 5 are no longer than those of pereiopods 2–4 and all are of similar shape. These features allow to clearly distinguish both species so P. nudus should be removed from the synonymy of O. transverus and considered a valid species. The morphology of the third maxilliped described above and the shape and relative length of the dactyli of pereiopods 2–5 support the exclusion of P. nudus from Pinnotheres Bosc, 1802 . The species is nevertheless retained temporally in Pinnotheres awaiting the collection of additional material.

Figures

FIGURE 4. A – D, Opisthopus transversus Rathbun, 1918 from Punta San Miguel, Todos Santos Bay, Ensenada, Baja California, Mexico. E-H, Pinnotheres nudus Holmes, 1895, from Santa Cruz, California, U. S. A. Adult female: A, E, carapace, dorsal view; B, F, abdomen; C, G, right and left cheliped respectively, outer aspect; D, H, third maxilliped, outer view. A – C, scale 1: 0.5 mm; 2: 0.1 mm; E – H, not to scale.