Enigmatheres canfieldi ( Rathbun, 1918 ) Rathbun, 1918

Campos, Ernesto, 2009, Pacific Ocean, with a reappraisal of the subfamily Pinnotherinae de Haan, 1833 (Crustacea: Brachyura: Pinnotheridae), Zootaxa 2022, pp. 29-44 : 32-33

Enigmatheres canfieldi ( Rathbun, 1918) , new combination

( Fig. 1 A–E)

Raphonotus subquadratus Rathbun, 1904: 106 (part: specimen from Monterey, California, fide Rathbun, 1918). (Not Raphonotus subquadratus Dana, 1851 ).

Fabia canfieldi Rathbun, 1918: 12 , 101, 102, 106–107, pl. 24, fig. 5–7, text-fig. 57; Schmitt, 1921: 254 –255, pl.39, fig. 5–6: Balss, 1957: 1420; Schmitt et al., 1973: 7, 22: Dai, 1980: 136; Campos, 1996b: 1174 –1175; Ng et al., 2008: 249 (listed).

Distribution and host. Known from only Monterey, California, the type locality; in folds of the keyhole limpet Megathura crenulata (Sowerby, 1825) .

Material examined. Holotype of Fabia canfieldi Rathbun, 1918: 1 damaged female ( USNM 8445).

Redescription of holotype. Carapace damaged (crushed as to be for the most part beyond description). Front devoid of setae, with short, longitudinal median depression.

Third maxilliped obliquely placed in buccal cavity; ischium, merus indistinguishably fused; palp 3- segmented; carpus larger than conical propodus; dactylus small, narrow, inserted on middle third of medioventral margin of propodus. Exopod with 2-segmented flagellum ( Fig. 1 A–B).

Chelipeds elongated ( Fig. 1 C), palm slightly increasing in width distally, fingers shorter than palm, slightly deflexed, ventral margin of propodus slightly concave; fingers not gaping when closed, setose along inner surface; with prehensile tooth at proximal third of cutting edge of dactylus, smaller one at base of pollex; cutting edge of both fingers with small teeth ( Fig. 1 C).

Walking legs subcylindrical, naked, relative length 2> 3> 1> 4; second leg asymmetrical, right 1/3 longer than left; WL1 stouter than others; propodi slightly curved, slightly stouter at distal end than at proximal, except right WL2 which tapers to distal end; longest right WL2 dactylus differs from others dactili in being nearly straight to tip; other dactyli shorter, slender, conical, more curved toward hooked, hard tip ( Fig. 1 E).

Abdomen of six somites and telson well separated.

Remarks. The presence of a thin, translucent and soft carapace, enlarged carpus of MXP3 and asymmetrical WL2 are characters that suggest Enigmatheres is related to the genus Austinotheres Campos, 2002 . Enigmatheres differs from Austinotheres in the gently curved outer margin of the MXP3 ischiummerus, and by the insertion of the dactylus on the middle third of the ventral margin of the conical propodus. Austinotheres has an obtuse angle on the MXP3 outer margin and the dactylus of this appendage is inserted further distally on the propodus. Austinotheres can be also distinguished from Enigmatheres by its slender and long walking legs, with blade-shaped and slightly curved dactyli. Both Enigmatheres and Austinotheres can be distinguished from other pinnotherids by the asymmetrical WL2 and the shape and relative length of the MXP3 palp articles, particularly the carpus being larger than the propodus, as well as the small and narrow dactylus being inserted medially or distally on the medioventral margin of the propodus. Others genera currently in the Pinnotheridae have symmetrical walking legs and/or the dactylus of MXP3 is inserted on the middle or proximal ventral margin of a propodus which is always larger than the carpus.

Figures

FIGURE 1. Enigmatheres canfieldi (Rathbun, 1918) new combination, Monterey, California (USNM 8445). Adult female: A – B, left outer and right inner view of MXP 3; C, left cheliped; D, pollex and dactylus of left cheliped; E, left and right walking legs, respectively. Scales: A = 0.57 mm; B = 0.47 mm; C – D not at scale; E = 1 mm.