Brankocleistostoma Števčić, 2011

Lasley Jr, Robert M., Anker, Arthur & Naruse, Tohru, 2024, Two new species and a new record of infaunal crabs (Decapoda: Brachyura: Pinnotheridae and Varunidae) from Oman and Saudi Arabia, Zootaxa 5476 (1), pp. 207-229 : 215

Brankocleistostoma Števčić, 2011

Brankocleistostoma Števčić, 2011: 134 .

Type species. Brankocleistostoma fossulum (Barnard, 1955) = Paracleistostoma fossula Barnard, 1955 , by original designation.

Remarks. Naruse & Clark (2009, as Paracleistostoma ) and Ng (2012) compared the presently monotypic genus Brankocleistostoma with what they considered to be its closest gaeticine relative, Gopkittisak . In addition to having a relatively broad carapace, unlike the other gaeticine genera, both Brankocleistostoma and Gopkittisak lack the longitudinal sternal sulcus on the anterior sternites to accommodate the filtering setae of Mxp3, which seems to be an outdated character previously used to diagnose Brankocleistostoma ( Davie & Ng 2007; Števčić 2011; Naruse 2015). On the other hand, in both Brankocleistostoma and Gopkittisak , the anterior sternites 1–3 are depressed to accommodate the Mxp3 setae. Several other genera with a similar sternal morphology were subsequently included in the Gaeticinae (see Naruse 2015: table 2).

Until the present study, only female specimens of B. fossulum were known (Barnard 1955; Ng 2012). As in most brachyuran crabs, male characters, especially the degree of fusion of male pleonites and morphology of G1, are important for generic and subfamilial assignments. Therefore, a diagnosis of the first known male of B. fossulum is provided below.

As mentioned above, in the subfamily Gaeticinae , as currently defined, the male pleonites 3–6 are functionally fused and immovable ( Davie & Ng 2007; Guinot et al. 2018). However, in B. fossulum , the fusion affects only the pleonites 4–6, with the suture between the pleonites 3 and 4 being well defined; therefore, pleonite 3 is capable of some limited flexing ( Fig. 5C , 6D ). Examination of more males is needed to confirm this character, which would have some consequences for the diagnosis of the subfamily.

In B. fossulum , G1 is stout and relatively straight, with a curved, chitinous, distal “beak” emanating from near a “shoulder” (rounded lobe); the tip is partially obscured by short, stiff, simple setae. All these features are also present in G1 of Gopkittisak ( Naruse & Clark 2009; Komai 2011; see also below), suggesting a close relationship between Gopkittisak and Brankocleistostoma , although the absence (in the former genus) or presence (in the latter genus) of teeth on the anterolateral margin of the carapace clearly separates the two genera ( Naruse 2015).

Figures

FIGURE 5. Brankocleistostoma fossulum (Barnard, 1955), male (6.7/4.1), Farasan Islands, Saudi Arabia, FLMNH UF 36973: A, habitus, dorsal; B, anterior surface of carapace and buccal frame, anterior (frontal); C, sternum, pleon, telson and Mxp3, ventral; D, right chela, outer; E, left chela, outer. Photographs by R. Lasley.

FIGURE 6. Brankocleistostoma fossulum (Barnard, 1955), male (6.7/4.1), Farasan Islands, Saudi Arabia, FLMNH UF 36973: A, left G1, dorsal; B, same, ventral; C, third maxilliped, ventral; D, pleon and telson, ventral. Scales: 1 mm.