Pseudathanas Bruce 1983

Genus Pseudathanas Bruce, 1983

Alberta Kazmi & Kazmi 2010: 233.

Emended diagnosis. Body not compressed, not particularly slender. Carapace smooth, unarmed dorsally and laterally. Rostrum broadly triangular, unarmed dorsally and ventrally. Orbital teeth absent or reduced. Pterygostomial angle rounded, not protruding; posteroventral margin of branchiostegite fringed with long plumose setae; cardiac notch well developed. All pleonites with distoventrally rounded pleura; sixth pleuron with articulated plate. Telson moderately broad, with two pairs of stout spiniform setae on dorsal surface; posterior margin rounded, with two pairs of spiniform setae; anal tubercles absent. Eyes well developed, partly visible or concealed in dorsal view; cornea large, well pigmented. Antennular peduncle stout, relatively short; stylocerite well developed, distally acute, overreaching mid-length of second article of peduncle; ventromesial carina armed with tooth; second article not particularly elongate; lateral flagellum with short fused portion and well-developed accessory ramus with aesthetascs. Antenna with basicerite stout, unarmed or armed with small sharp tooth; scaphocerite with well-developed blade and small distolateral tooth. Mandible with two-articulated palp; molar and incisor processes well developed. Third maxilliped with well-developed exopod; coxa with acutely produced lateral plate; ultimate article tapering into corneous tip, unarmed. First pereiopods (= chelipeds) enlarged in both sexes, unequal or subequal in size, asymmetrical or subsymmetrical in shape, carried flexed beneath body when not in use; ischium robust, with dorsal and ventral margins rugose and armed with short spiniform setae; merus with ventrolateral margin rugose and armed with prominent tooth near its mid-length, ventral surface deeply excavated; carpus vase- or cup-shaped, without setal rows on mesial surface; chelae more or less swollen; palm with tubercles and row of setae on ventral surface; fingers of major chela armed with large teeth, without snapping mechanism. Second pereiopod with ischium unarmed; carpus with four or five subarticles; chela simple, without modifications. Third and fourth pereiopods moderately slender; ischium armed with one or two spiniform seta(e); merus unarmed; carpus with one spiniform seta on distoventral margin; propodus with several spiniform setae; dactylus simple, conical. Fifth pereiopod with ischium armed with one spiniform seta; merus unarmed; carpus with one spiniform seta on distoventral margin; propodus with at least two spiniform setae and short cleaning brush; dactylus simple. Second male pleopod with appendix masculina subequal in length to appendix interna; second female pleopod with appendix interna only. Uropodal exopod with diaeresis armed with row of stout spiniform setae. Gill-exopod formula provided in Table 3.

1, 2

same remarks as for Table 1. 3 needs confirmation.

Species included. Type species P. darwiniensis Bruce, 1983; P. banneri (Kazmi & Kazmi, 2010) comb. nov.

Remarks. The alpheid genus Pseudathanas was originally established to accommodate only the type species Pseudathanas darwiniensis Bruce, 1983, a small, peculiar, intertidal shrimp found in silted rock pools near Darwin, Northern Territory, Australia (Bruce 1983). Pseudathanas was separated from the closely related genus Athanas by the much shorter rostrum, the greatly reduced orbital teeth, the proximally thickened antennal flagella, the unequal and asymmetrical chelipeds, and the presence of stout spiniform setae on the transverse suture (diaeresis) of the uropodal exopod (Bruce 1983), this latter feature being unique within the Alpheidae and therefore most diagnostic of the genus. No other specimens of Pseudathanas have been reported since Bruce’s (1983) description of P. darwiniensis and the genus remained monotypic for almost 40 years.

In the poorly known, not peer-reviewed publication (book) on the caridean shrimps of Pakistan, Kazmi & Kazmi (2010) established the alpheid genus Alberta Kazmi & Kazmi, 2010 for Alberta banneri Kazmi & Kazmi, 2010, based on a single ovigerous female from Bulleji, near Karachi. All material listed in this study, including the holotype of A. banneri, was supposedly deposited in the Marine Reference Collection and Resource Centre, University of Karachi, Pakistan. The generic diagnosis of Alberta, as well as the description of its type species A. banneri, are very poor compared to modern standards in caridean taxonomy. Nevertheless, the semi-diagrammatic illustrations of A. banneri provided by Kazmi & Kazmi (2010) are sufficient to suggest that this taxon belongs to the genus Pseudathanas. Most importantly, the diaeresis of the uropodal exopod of A. banneri is adorned with the same row of strong spiniform setae as in P. darwiniensis (cf. Bruce 1983: fig. 2F, 5C; Kazmi & Kazmi 2010: fig. 108B). The collection of three specimens (one subsequently lost) of a species with all characteristics of A. banneri in northern Oman (see below) eliminated any lingering doubts about its identity. Therefore, Alberta is herein placed in the synonymy of Pseudathanas and the Omani material is reported as Pseudathanas banneri (Kazmi & Kazmi, 2010) comb. nov. The generic diagnosis of Pseudathanas provided above was emended to accommodate several features of P. banneri that are novel for the genus, especially the dorsally covered eyes, the subequal and subsymmetrical chelipeds, and the second pereiopod carpus with four subarticles (carpal subdivisions).

As suggested by Bruce (1983), Pseudathanas is closely related to Athanas, from which it differs essentially by the armature of the diaeresis.All other morphological characters listed by Bruce (1983) to distinguish Pseudathanas from Athanas are invalid as they are present in some more recently described species of the latter genus (see also above). These characters are the marked reduction of the rostrum (also observed in A. iranicus, A. daviei, A. manticolus, A. claereboudti sp. nov.); the absence of supra-, extra-, or infra-corneal teeth (absent or greatly reduced in A. iranicus, A. daviei, A. manticolus and A. claereboudti sp. nov.); the well-developed, dissimilar chelipeds, apparently in both males and females (female minor cheliped unknown in P. darwinensis) (variable in Athanas, with similar condition found, for instance, in A. shawnsmithi); and the proximally thickened antennal flagellum (also observed in A. iranicus, A. shawnsmithi, A. manticolus and A. claereboudti sp. nov.). Pseudathanas also shares many features with Athanopsis Coutière, 1897 and Leptathanas De Grave & Anker, 2008, differing from both of these genera by the unique armature of the uropodal diaeresis; from Athanopsis by the distally pointed rostrum (vs. rounded in Athanopsis); and from Leptathanas by the relatively well developed rostrum (reduced in Leptathanas) and the much slenderer walking legs and antennular peduncles (very stout in Leptathanas) (cf. Coutière 1897, 1899; Anker & Ahyong 2007; De Grave & Anker 2008; Anker 2011b, 2012; Marin et al. 2014, see also Fig. 10). The long plumose setae on the posteroventral margin of the branchiostegite are present in Pseudathanas, but also in the not closely related Orygmalpheus De Grave & Anker, 2000 and (with lesser development) in some other alpheid genera (De Grave & Anker 2000; Anker et al. 2006a).

Anker et al. (2006a) performed a cladistic analysis of morphological characters and recovered Pseudathanas and Athanas in sister position within a larger “athanoid” clade (clade AP), together with Athanas (paraphyletic), Arete Stimpson, 1860 and Aretopsis De Man, 1910. In the molecular analysis of the Alpheidae, Chow et al. (2021) also recovered an athanoid clade (clade S-V), which further included Acanthanas Anker, Poddoubtchenko & Jeng, 2006 (Anker et al. 2006b). Pseudathanas and Leptathanas were not included in their analysis because no suitable material of these genera was available at that time. Interestingly, Chow et al. (2021) showed Athanas and Arete to be non-monophyletic due to the positions of two species of Athanopsis and one species of Athanas, respectively. Surprisingly, and difficult to explain from the morphological point of view, Rugathanas Anker & Jeng 2007 was excluded from clade S-V despite the presence of several synapomorphic features linking it to other athanoid genera (Anker & Jeng 2007). Based on its overall morphology, Pseudathanas appears to be closest to Athanopsis and is most likely nested within the Athanas + Athanopsis lineage of Chow et al. (2021), whilst the phylogenetic position of the highly derived Leptathanas remains more enigmatic. The entire athanoid clade will definitively need more phylogenetic efforts devoted to it, in view of interesting evolutionary convergences due to symbiotic lifestyles (both infaunal and epibiotic, see Anker & Jeng 2007).