Rathbunixa Theil & Felder 2020, n. gen.

Genus Rathbunixa n. gen.

urn:lsid:zoobank.org:act: 316B06E6-4F1B-4109-A608-2BAC7E426737

TYPE SPECIES. — Rathbunixa sayana (Stimpson, 1960) n. comb. [Pinnixa].

DIAGNOSIS. — Carapace broad, regions clearly defined, cardiac ridge sharp, not extending entirely across carapace. Third maxilliped ischiomerus subtrapezoidal; propodus and dactylus longer than carpus, shorter than ischiomerus; dactylus elongate, inserting near base of propodus, reaching beyond end of propodus. Chelipeds hairy or pubescent, no lines of setae or tubercles on palm; fixed finger strongly reduced or deflexed, sexually dimorphic, ontogenetically variable. Ambulatory legs elongate, slender; relative lengths P4> P3> P2> P1. Male pleon tapering toward end, telson subtriangular; lacking gonopodal plate.

ETYMOLOGY. — Named for Mary J. Rathbun, who carefully cataloged, examined and described a large percentage of the pinnotherids presently known to mankind, including this genus. Gender feminine.

ADDITIONAL SPECIES. — Rathbunixa affinis (Rathbun, 1918) n. comb. [Pinnixa];

Rathbunixa californiensis (Rathbun, 1894) n. comb. [Pinnixa]; Rathbunixa occidentalis (Rathbun, 1894) n. comb. [Pinnixa]; Rathbunixa pearsei (Wass, 1955) n. comb. [Pinnixa].

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

Rathbunixa pearsei n. comb. — ULLZ 4421, ULLZ 4425, ULLZ 5513, ULLZ 5590 (8), ULLZ 7024, ULLZ 14001, ULLZ 14006 (2), ULLZ 14007, ULLZ 14010, ULLZ 14082, ULLZ 14085, ULLZ 14515 (3), ULLZ 14910, ULLZ 14913, ULLZ 15032, ULLZ 16744 (2) (Fort Pierce, FL, USA), ULLZ 13947 (Marco Island, FL, USA); MNHN-IU-2017-9366 (= former ULLZ 7026); ULLZ 4496, ULLZ 4498, ULLZ 7401, ULLZ 13542 (4), ULLZ 13547 (2), ULLZ 17455 (2) (Tampa Bay, FL, USA), ULLZ 15749 (Bayport, FL, USA), ULLZ 2594 (5), ULLZ 15671 (Mobile Bay, AL, USA), ULLZ 14041 (Bay St. Louis, MS, USA), ULLZ 14016 (Horn Island, MS, USA), ULLZ 17466, ULLZ 17470 (offshore, northeastern Gulf of Mexico), ULLZ 2593 (Cheniere au Tigre, LA, USA), ULLZ 2596 (Corpus Christi, TX, USA);

Rathbunixa sayana n. comb. — USNM 36323 (Rhode Island, USA), USNM 173396 (North Carolina, USA); MNHN-IU-2017-9367 (= former ULLZ 7397), ULLZ 14906 (2) (Fort Pierce, FL, USA), USNM 48438 (Sarasota Bay, FL, USA).

REMARKS

Morphological similarities among some species of this genus have been noted previously, though always between species sharing an ocean basin such as the eastern Pacific pair, R. affinis and R. occidentalis, and the western Atlantic pair, R. pearsei and R. sayana (Rathbun 1918; Wass 1955; Zmarzly 1992). We have observed great variability in the morphological characters that define R. pearsei and that are reported to differentiate it from R. sayana. Wass (1955) described the former species to separate specimens found in northwestern Florida from R. sayana, the distribution of which was known at that time to range from Massachusetts to Sarasota Bay, in southwestern Florida. Later records extended the distribution of R. sayana to Grand Isle, Louisiana, and Brazil (Schmitt et al. 1973). In addition, we have samples that fit the morphological characters of R. sayana from Corpus Christi, Texas. We also have collections of specimens matching the description of R. pearsei from Atlantic coast of Florida, Gulf of Mexico waters in southern Florida, and Gulf Shores, Alabama. All these samples are genetically very close in relationship (Fig. 1). This suggests that R. pearsei should be regarded as a junior synonym of R. sayana. However, the type of R. sayana is not extant, and the type locality is the mouth of Beaufort Harbor, North Carolina, a location we were unable to represent among collection sites for our samples of R. sayana, all of which are well to the south. Thus, we for now lack genetic evidence upon which to base genetic re-evaluation of these two taxa, and retain both names.

When Rathbun (1894) described Pinnixa occidentalis and P. californiensis she noted the resemblance between the two, but nonetheless treated them as separate species, though she later synonymized them (Rathbun 1918). However, more recently smaller and less granulate variations of R. occidentalis have been reported, indicating that this taxon should be treated as a “group of allied species” (Hart 1982). The specimen we examined is probably one of these variants. Whether or not some of these variants could possibly match the description of R. californiensis requires further investigation. For now, we elect to retain R. californiensis as a separate taxon, following Ng et al. (2008). The material of R. occidentalis included here was collected in Panama, expanding the southern limit of the species range, which was formerly Magdalena Bay, in Mexico (Schmitt et al. 1973). Despite the fact that we were unable to analyse additional samples of the R. californiensis – occidentalis complex, we provisionally assign both species to this genus, based on their long recognized relationship.