Athanas Leach 1814

Genus Athanas Leach, 1814

Athanas Leach 1814: 401.

Emended diagnosis (simplified and updated from Anker & Jeng 2007). Body not compressed, slender to moderately stout. Carapace smooth, glabrous or moderately setose, typically unarmed dorsally, sometimes with small postrostral tubercle. Rostrum typically elongate, sometimes lanceolate in dorsal view, rarely short, subtriangular; dorsal margin unarmed or with minute teeth; ventral margin unarmed. Orbital teeth usually present as one pair of extra-corneal tooth, often well developed and sometimes protruding beyond anterior margin of eye, and one pair of infra-corneal teeth; occasionally infra-corneal teeth reduced or absent; extra-corneal teeth occasionally reduced to small bumps; supra-corneal teeth absent (often) or present (rarely). Pterygostomial angle rounded or angular, sometimes produced as sharp tooth; branchiostegite with scarce setae; cardiac notch well developed. First to fourth pleonites with distoventrally rounded or bluntly angular pleura; fifth pleonite with pleuron angular or subacute distoventrally; sixth pleuron with articulated plate. Telson moderately slender to broad, tapering distally, with two pairs of stout spiniform setae on dorsal surface; posterior margin rounded or straight, with two pairs of spiniform setae; anal tubercles absent. Eyes well developed, at least partly visible in dorsal view; cornea large, well pigmented, sometimes slightly reduced. Antennular peduncle stout, relatively short; stylocerite well developed, distally acute or subacute, usually overreaching mid-length of second article, sometimes its distal margin; ventromesial carina armed with tooth; second article not or variously elongate; lateral flagellum with short fused portion and well-developed accessory ramus with aesthetascs.Antenna with basicerite moderately to very stout, armed with sharp tooth; scaphocerite with well-developed blade and variously developed distolateral tooth. Mandible with two-articulated palp; molar and incisor processes well developed. Third maxilliped with well-developed exopod; coxa with moderately produced lateral plate; ultimate article tapering into corneous tip, often with small spiniform seta(e). First pereiopods (= chelipeds) highly variable in development, often sexually dimorphic, typically greatly enlarged in males, sometimes in both sexes, subequal or very unequal in size, subsymmetrical or highly asymmetrical in shape, carried extended or flexed beneath body when not in use; basis typically with rudimentary exopod; ischium robust, with dorsal margin or both dorsal and ventral margins often armed with spiniform setae; merus with ventrolateral margin smooth or dentate, ventral surface flattened or deeply excavated; carpus variable, cylindrical, vase- or cup-shaped, without setal rows on mesial surface; chelae more or less enlarged and swollen, palm with or without tubercles and row of setae on ventral surface; fingers of chelae unarmed or armed with teeth, in males or in both sexes, without snapping mechanism. Second pereiopod with ischium unarmed; carpus typically with five, rarely four or six, subarticles; chela simple, without modifications. Third and fourth pereiopods varying from very slender to moderately stout; ischium usually armed with one spiniform seta, rarely with two spiniform setae or unarmed; merus unarmed; propodus with several spiniform setae or short stiff setae on ventral margin; dactylus more or less slender, simple or biunguiculate. Fifth pereiopod with ischium unarmed or armed with one spiniform seta; merus unarmed; propodus with or without spiniform setae and well-developed cleaning brush; dactylus simple or biunguiculate. Second male pleopod with appendix masculina equal in length or exceeding appendix interna, sometimes reaching beyond endopod; second female pleopod with appendix interna only. Uropodal exopod with unarmed, sinuous or straight diaeresis. Gill-exopod formula summarised in Table 1.

1 lateral plate on coxa; 2 strap-like epipods of Chace (1988); 3 if present, rudimentary.

Species included. Type species A. nitescens (Leach, 1814); all species listed in De Grave & Fransen (2011) + A. manticolus Ďuriš & Anker, 2014; A. mendax Ahyong, 2015; A. alpheusophilus Marin, 2017; A. philippei Anker & Ďuriš 2022; A. exilis Komai & Henmi, 2023; A. claereboudti sp. nov. (described below).

Remarks. Athanas and allied genera were reviewed and taxonomically redefined by Anker & Jeng (2007). However, the rapidly increasing number of species, especially among the infaunal “commensals”, resulted in the much greater morphological heterogeneity of Athanas compared to the definition of the genus given by Anker & Jeng (2007). In the herein emended generic diagnosis of Athanas, the author attempted to take into consideration all important novel features described in the genus (including the below-described new species) since its redefinition by Anker & Jeng (2007). It is interesting to note that the infaunal lifestyle that evolved in some lineages of Athanas and Salmoneus resulted in remarkable convergences between these two genera, for instance, in the shape of the frontal margin of the carapace (decrease in length of the rostrum and reduction of orbital teeth), reduction of the cornea size, strengthening of the antennal flagella, and appearance of either setal brushes (Athanas) or setal rows (Salmoneus) on the chelae of the first pereiopods.

The recent phylogenetic hypothesis for the Alpheidae based on molecular data (Chow et al. 2021) showed a non-monophyly of Athanas in its present composition (see also discussion under Pseudathanas). Another important result of this study was the lack of support for the two currently recognised, informal species groups within the genus, which were in use since Coutière (1899), namely the A. nitescens (Leach, 1814) group (containing species with extended chelipeds) and the A. dimorphus Ortmann, 1890 group (containing species with ventrally folded chelipeds). Therefore, the herein provided diagnosis of Athanas should be used with some reservation as further taxonomic rearrangements, with redefinitions of genera and their diagnostic features, are expected in the near future.