Nullibrotheini Soleglad & Fet, 2003

Soleglad, Michael E. & Fet, Victor, 2003, High-level systematics and phylogeny of the extant scorpions (Scorpiones: Orthosterni), Euscorpius 2003 (11), pp. 1-175 : 96

Tribe Nullibrotheini Soleglad & Fet , new tribe

Type Genus. Nullibrotheas Williams, 1974 .

Composition. This new monotypic tribe is described here. It includes a single monotypic genus Nullibrotheas .

Distribution. Mexico (southern Baja California).

Taxonomic history. The single known species of the genus Nullibrotheas has been originally assigned to Chactidae as “ Broteas ” or Broteochactas by earlier authors. Williams (1974, 1980), who described this genus, placed it in Vaejovidae . Stockwell (1989, 1992)

transferred Nullibrotheas back to Chactidae ; see Sissom (2000a, 2000c).

Biogeographic history. Baja California Peninsula separated from the Mexican mainland ca. 5.5 Ma ago. The Cape region of Baja California Sur, where genus Nullibrotheas is found ( Williams, 1974, 1980), has been isolated in Pliocene, which led to formation of cryptic species (Grismer, 2000; Riddle et al., 2000; Gantenbein et al., 2001a). Such an isolation could facilitate the survival of a relict lineage which led to Nullibrotheas .

Diagnosis. Synapomorphies. Patella external est series with additional accessory trichobothrium; patella ventral surface with additional accessory trichobothrium; ventral edge of cheliceral movable finger with dentition; lateral carinae of metasomal segment IV present; chelal V1 carina distal termination curves towards the internal finger condyle. Important Symplesiomorphies. Chelal trichobothria Db basal, Dt situated at palm midpoint; patellar trichobothria series em 1 –em 2 and esb 1 proximal of segment midpoint; neobothriotaxy Ch1 present on patellar ventral surface; neobothriotaxy Ch1 present on patellar external surface.

Discussion. Nullibrotheas shows a close affinity to its sister tribe Chactini . In particular, the unique major fixed neobothriotaxic patterns for the pedipalp patella exhibited in both, type Ch1, are quite distinct. All patellar external series match in position and pattern, though in Nullibrotheas we see an additional accessory trichobothrium in the est series ( Fig. 86). The patellar ventral series also exhibits an additional accessory trichobothrium (six total trichobothria in the ventral series in Nullibrotheini and five in Chactini ). Only one species is defined in this genus, N. allenii , but its range in Baja California Sur is quite extensive, extending from Mulege in central Baja to Cabo San Lucas at the Cape ( Williams, 1974: Fig. 5). Within this geographical range considerable overall size differences are exhibited, populations in the La Paz area reach sizes of 60 mm. whereas adults in most other areas range from 30–45 mm. In addition, color populations are present over this distributional range. These observations ( Williams, 1974) are based on the examination of over 280 specimens. Williams decided this variability best be attributed to a single variable species. In support of this conclusion, based on the limited number of specimens examined by us, we detect no variability in the number of accessory trichobothria, showing consistency to the fixed neobothriotaxic pattern exhibited in this chactid subfamily. In scorpion groups that exhibit variability in neobothriotaxy, this variability can be useful in determining phylogenetic relationships within the group (e.g., Euscorpius , Anuroctonus , Hadrurus ).