Scleroplax Rathbun, 1894

Theil, Emma Palacios & Felder, Darryl L., 2020, Phylogeny of the genus Pinnixa White, 1846 (Crustacea, Brachyura, Pinnotheridae) and allies inferred from mitochondrial and nuclear molecular markers, with generic reassignment of twenty-one species, Zoosystema 42 (6), pp. 85-103 : 98

Genus Scleroplax Rathbun, 1894

Scleroplax Rathbun, 1894: 250 .

TYPE SPECIES. — Scleroplax granulata Rathbun, 1894 , by monotypy when genus was erected.

ORIGINAL DIAGNOSIS BY RATHBUN (1918). — “Carapace transverse, subpentagonal, hard, very convex, regions scarcely indicated, lower or true antero-lateral margin curving gradually into postero-lateral margin, not forming an angle with it as in Pinnixa . Ambulatory legs similar, third longest but not unusually long, fourth not noticeably reduced. Ischium of outer maxillipeds rudimentary, merus oblique, palpus three-jointed, the last joint articulating near proximal end of preceding joint. Only a single species known.”

DIAGNOSIS OF THE GENUS AS MODIFIED BY CAMPOS (2006). — “Carapace hard, subheptagonal, highly convex dorsally, anterolateral margins not forming angle with posterolateral margins; MXP3 [= third maxilliped] slightly oblique, covers buccal cavity, ischio-merus subtrapezoidal, propodus extending to end of dactylus, both spoonshaped and larger than carpus. WL1-4 [= walking leg] of similar shape, third pair slightly longer, fourth not noticeably reduced.”

DIAGNOSIS. — (Modified from Rathbun 1918 and Campos 2006). Carapace transverse, subpentagonal or oblong, hard, very convex, anterolateral margins not forming an acute angle with posterolateral margins; cardiac ridge, if present, not extending entirely across carapace. Third maxilliped slightly oblique, covering buccal cavity, ischiomerus subtrapezoidal; propodus and dactylus elongate, longer than carpus; dactylus inserting near base of propodus, reaching end of propodus or slightly beyond. Male cheliped strong, fixed finger somewhat shortened, straight; female cheliped feeble, fixed finger straight; external palm surface sometimes with longitudinal line of tubercles. Walking pereopods subequal, cylindrical, relative lengths P4> P3 ≥ P2> P5. Male pleon tapering toward end, telson subsemicircular; first pleonal somite lacking gonopodal plate between gonopods.

ADDITIONAL SPECIES. — Scleroplax faba (Dana, 1851) n. comb. [ Pinnixa ];

Scleroplax franciscana ( Rathbun, 1918) n. comb. [ Pinnixa ]; Scleroplax littoralis (Holmes, 1894) n. comb. [ Pinnixa ];

Scleroplax schmitti ( Rathbun, 1918) n. comb. [ Pinnixa ]; Scleroplax tubicola (Holmes, 1894) n. comb. [ Pinnixa ].

MATERIAL EXAMINED. — In addition to the material included in the phylogenetic analyses ( Table 1 ) the following samples were available for examination:

Scleroplax franciscana n. comb. — ULLZ 5625 , ULLZ 5626 (Bodega Bay, CA, USA) ;

Scleroplax littoralis n. comb. — ULLZ 8505 (10) (Poulsbo, WA, USA), ULLZ 14072 (4) (Gamble Bay, WA, USA) ;

Scleroplax schmitti n. comb. — ULLZ 14036 , ULLZ 14842 (8) (Baranof Island, AK, USA), ULLZ 14117 , MNHN-IU-2017-9369 = former ULLZ 14119 (Japonski Island, AK, USA) ;

Scleroplax tubicola n. comb. — ULLZ 14116 (Middle Island, AK, USA), ULLZ 14118 (Japonski Island, AK, USA) .

REMARKS

Genetic distances and the morphological differences observed among some of the species in this group are similar to those shown among conspecific populations in other pinnotherid genera, for instance Austinixa , Tumidotheres Campos, 1989 , or Tunicotheres Campos, 1996 . Furthermore, for some species there seems to be striking variation in key characters between juveniles and adults. For example, juveniles of P. littoralis and P. faba appear to be extremely difficult to discriminate ( Zmarzly 1992). A more detailed investigation with larger sample sizes and markers appropriate to determine variability between populations of these species is required to clarify phylogenetic relationships within and among them. In addition, knowledge of host associations is required to accompany samples, as these taxa might represent species complexes of separate, but morphologically similar, populations that have adapted to different hosts, which may also be reflected in variations between inshore and offshore samples.

The only specimen of Pinnixa scamit available for molecular analyses and morphological examination was a juvenile (UF 11969), and had therefore been identified provisionally. Genetically it was closely allied to Scleroplax , however, morphologically it showed characters similar to those in Rathbunixa n. gen. It had long slender legs, somewhat compressed, and a sculpted carapace. Despite the results of the molecular analysis, we choose not to transfer Pinnixa scamit to the genus Scleroplax , until specimens definitively identifiable as P. scamit are available for analysis.