Alphacheles Klompmaker, Martin, Hyžný, Bowman, Phillips & Portell, 2025, n. gen.

Genus Alphacheles n. gen. urn:lsid:zoobank.org:act: D5A2F0B5-3E68-403C-A751-6951DE740D9F TYPE SPECIES. — Callianassa zeta Rathbun, 1936 (Callianassa alpha Rathbun, 1935a; non Callianassa alpha Stenzel, 1935), by present designation. ETYMOLOGY. — The genus name is a combination of “alpha ”, referring to the homonymous species name Callianassa alpha, and “cheles” meaning “claw”. Gender: masculine. DIAGNOSIS. — As for the type species. REMARKS Shortly after the description of Callianassa alpha Rathbun, 1935a, it was revealed that the name had already been used by Stenzel (1935) for yet another fossil ghost shrimp assigned to Callianassa. A rectification was published in the following year, renaming C. alpha to C. zeta Rathbun, 1936. Callianassa zeta differs from all known extant and extinct ghost shrimp taxa by its tuberculate area (“densely punctate excrescence” sensu Rathbun [1935a]; “triangular patch of granules” sensu Feldmann et al. [2019]) at the base of the fixed finger which is present at the outer and inner lateral surfaces. This character has been considered a diagnostic feature of this species (Rathbun 1935a; Feldmann et al. 2019). Its taxonomic significance is herein elevated to the genus level, and hence a new genus is proposed to accommodate this species. So far, only propodi and dactyli are known for Alphacheles zeta (Rathbun, 1936) n. comb. Most specimens represent major claws, whereas in one case also a minor claw is identified (Fig. 5O). Their morphology is rather close to that of extant species of Gourretia and Paragourretia, based on which the new genus is classified within the family Ctenochelidae. Nevertheless, the familial placement of Alphacheles n. gen. should be considered preliminary until more complete material is found. Alphacheles n. gen. shares with the above-mentioned genera the following set of characters: major cheliped propodus distinctly longer than high and subrectangular in outline, relatively long fingers exceeding half of the propodus palm length, and dactylus occlusal surface with simple dentition (cf. Le Loeuff & Intès 1974; Sakai 2002, 2004; Ngoc-Ho 2003). These characters are shared also with Cretagourretia, an exclusively fossil genus known from the Early Cretaceous (Albian) of Spain. This set of characters mentioned above is rarely seen in other ghost shrimp families (Poore & Ahyong 2023). As mentioned above, Alphacheles n. gen. differs from all ghost shrimp genera known to date by the presence of a tuberculate area at the base of the fixed finger. It differs also from yet another exclusively fossil ctenochelid genus, Ahazianassa, from the Late Cretaceous (Maastrichtian) of Japan. Additionally, Alphacheles n. gen. possesses a more elongate palm than Ahazianassa does. Besides Callianassa alpha, Rathbun (1935a) described also “ C. alpha var.” from the Upper Eocene Jackson Group of Mississippi. A new variety of C. alpha is based on a single incomplete propodus and a pleon found at the same locality. Because the isolated propodus does not appear to show a densely tuberculate area at the base of the fixed finger, “ C. alpha var.” is not considered closely related to Alphacheles zeta n. comb. Given the large temporal separation of c. 25 million years, these specimens might represent a new species, but a restudy of the specimens is needed.