Sayixa, Theil & Felder, 2020

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 : 97-98

Genus Sayixa n. gen.

urn:lsid:zoobank.org:act:2312947B-988C-442F-B00C-8BCBCE273BC2

TYPE SPECIES. — Sayixa monodactyla (Say, 1818) n. comb. [ Pinnixa ].

ORIGINAL DESCRIPTION FOR PINNIXA [ PINNOTHERES ] MONODACTYLA ( SAY, 1818) . — “ P. monodactylum * (male) Thorax transverse; hands monodactyle. […]

Thorax transversely subeliptical, narrowing each side to the middle of the lateral edge, which is rounded, a tubercle each side marking the situation of the anterior lateral angles, surface punctured; orbits suborbicular; anntennae [sic], exteriors subequal to the breadth of the clypeus; hand oblong, somewhat quadrate; palm concave and ciliated in the middle, a spiniform angle instead of a finger, with a tooth at its base, and another at the base of the thumb larger; thumb abruptly incurved at base, rectilinear towards the tip, with an angle at the interior middle, tip acute, attaining the tip of the spiniform angle; feet, second, fifth and third pairs subequal, the latter rather larger, fourth pair larger, and with the fifth pair with somewhat dilated tibia; abdomen with a few larger punctures, terminal joint rounded at tip, entire, ciliated and attaining the tip of the geminate joints of the pedipalpi.

Length three tenths, breadth one half an inch.

This curious animal occurs in the Richmond Museum. Mr. J. Warrell, the proprietor of that interesting establishment, supposes it to be American, but whether from our eastern or western coast he could not say. It is particularity remarkable in having monodactyle hands, a character which in a very rigid arrangement would not only separate it from the genus Pinnotheres , but also from the preceding species as a distinct genus. The tibia of the fourth and fifth pairs of feet are somewhat dilated, but the corresponding tarsi are accidentally wanting in this specimen.”

DIAGNOSIS. — Carapace transversally subeliptical, wider than long, punctate, narrowing toward rounded lateral edges; anterolateral margins each with single lobiform tooth or tubercle near or just anterior to lateral extreme. Third maxilliped with ischiomerus subtrapezoidal; propodus and dactylus elongate, longer than carpus; dactylus inserting near base of propodus, reaching beyond end of propodus. Chelipeds heavy, palm lacking longitudinal lines of setae; cheliped fixed finger strongly shortened, reduced to spiniform angle, with sharp tooth at base of dactylus.

First two ambulatory legs (P2, P3) slender, P4 and P5 somewhat stouter; lengths P4> P3> P2> P5. Male pleon subtrapezoidal, somites 4-6 constricted; telson oblong subellipsoidal, much wider than long.

ETYMOLOGY. — Named for Thomas Say, author of the type species of this new genus, and first author to describe pinnotherid species after Linneaus.

MATERIAL EXAMINED. — In addition to the material included in the phylogenetic analyses ( Table 1 ) one sample was available for examination: MNHN-IU-2017-9368 (= former ULLZ 8569 ) (offshore, northern Gulf of Mexico) .

REMARKS

In describing the species Pinnotheres monodacytlum , later transferred to Pinnixa, Say (1818) indicated that this taxon presented characters that “would not only separate it from the genus Pinnotheres , but also from the preceding species as a distinct genus”. The “preceding species” he is referring to is Pinnotheres cylindricum , which would become later the type of the genus Pinnixa . He discusses in that work the differences between the two species and the genus Pinnotheres , but he chose to maintain both within the genus Pinnotheres . Later, in 1846, Adam White, assistant in the Zoological Deparment of the British Museum, established the genus Pinnixa for P.cylindrica on the basis of its carapace being much wider than long, its having a larger cheliped palm when compared to Pinnotheres , and on the relative lengths of the ambulatory legs. He, however, did not include what we herewith assign to Sayixa monodactyla n. comb. in the genus Pinnixa , most likely because he had not found the opportunity to examine it. According to Rathbun (1918), Sayixa monodactyla n. comb. had not been seen since the type was reported upon. Moreover, the type in Richmond Museum was, also according to her, probably not extant.