Pseudothelphusa, : Smalley & Adkison, 1984

Villalobos, José Luis & Alvarez, Fernando, 2010, Phylogenetic analysis of the Mexican freshwater crabs of the tribe Pseudothelphusini (Decapoda: Brachyura: Pseudothelphusidae), Zoological Journal of the Linnean Society 160 (3), pp. 457-481 : 475

PSEUDOTHELPHUSA

The genus Pseudothelphusa , composed of 23 species, is defined by four characters (node 12): cervical groove not reaching the anterolateral margin of the carapace (character 12); U- or V-shaped notch separating proximal and distal lobes of the caudo-marginal projection of the gonopod (character 49); proximal lobe of the caudo-marginal projection longer than wide (character 56); and proximal lobe of the caudo-marginal projection with straight internal carina (character 58).

The internal structure of the genus as revealed by the phylogenetic analysis shows several important changes with respect to the previous classification ( Rodríguez, 1982). First, Pseudothelphusa guerreroensis is situated in a separate branch because of the combination of eight characters (10, 25, 26, 27, 30, 52, 69, and 71) that describe its unique morphology. From these, the following are characters that are not shared with any other species in the genus: the merus of the third maxilliped as wide as long (character 26), with an anterior margin that gives the article a subrectangular shape (character 27); a rounded lobe at the base of the major chela’s fingers (character 30); and a distal lobe of the caudo-marginal projection oriented proximally. This set of characters prompted Alvarez & Villalobos (1994a) to place P. guerreroensis in the genus Tehuana ; however, the same authors ( Villalobos & Alvarez, 2003) later placed it back in Pseudothelphusa , a decision that is now supported by the present phylogenetic analysis.

Second, there is a group of six species ( D. pecki , P. dilatata , P. seiferti , P. nelsoni , P. parabelliana , and P. morelosis ) that comes out in five different arrangements ( Fig. 7 ). The close relationship of P. dilatata and P. seiferti (node 13) is based on three characters of the carapace: a smooth (character 6) and straight (character 7) superior frontal margin, and a cervical groove reaching the anterolateral margin of the carapace (character 12).

Third, it is relevant to note that D. pecki always appears to be closely related to P. nelsoni and P. parabelliana (nodes 14 and 15), indicating that it should be accommodated in Pseudothelphusa . The characters that support this relationship are: a superior frontal border of the carapace granulate (character 6) and inclined towards the midline (character 7); a smooth space between the median and lateral epistomal teeth (character 25); a slender gonopod (character 33); and the similarity of the distal lobe of the caudo-marginal projection of the gonopod (character 50). The gonopod of D. pecki is esentially that of Pseudothelphusa: Smalley & Adkison (1984, p. 132) had already established the strong similarities between the two genera, justifying the new genus based mostly on the orientation of the apex cavity, which is only a small modification from the typical gonopod of Pseudothelphusa . The same authors also considered that the gonopod morphology of D. pecki was very similar to that of P. nelsoni , an observation that is now confirmed with the phylogenetic analysis presented here. Therefore, Disparithelphusa will now be considered a synonym of Pseudothelphusa .

Fourth, the remaining 15 species of Pseudothelphusa , starting with P. dugesi , appear in the same arrangement in all ten trees obtained (node 16). The characters that define this group are: frontal portion of the carapace slightly convex (character 10); posterior margin of the carapace concave in most species (character 17); distal crest of the caudo-marginal projection curved caudally (character 59); and inferior margin of mesial process convex (character 71). The grouping of these species is consistent with their distribution patterns. Pseudothelphusa digueti occurs in Lake Chapala, Jalisco, and is in its own branch. Pseudothelphusa dugesi , P. americana , and P. doenitzi , are distributed in central Mexico in Morelos, Puebla, and Oaxaca, respectively. They all share a subtriangular mesial process, with a straight, superior margin, and a short and somewhat rounded distal lobe of the caudo-marginal projection. Node 19 is the splitting point for four species from Guerrero ( P. belliana , P. hoffmannae , P. granatensis , and P. mexicana ) characterized by a caudo-marginal projection with an acute distal lobe and an oval-shaped proximal lobe that expands proximally, and a mesial process that ends in one or several tips. This group separates from the remaining eight species distributed along the western slope of Mexico. Developing from node 20 are the branches that group eight species distributed along the Pacific slope from Jalisco to Sonora ( P. peyotensis and P. nayaritae , Nayarit; P. leiophrys , Colima; P. terrestris , and P. jouyi , Jalisco; P. rechingeri , Sinaloa; P. lophophallus , Durango; P. sonorensis , Sonora). In all of them the distal lobe of the caudo-marginal projection appears either reduced or absent.

Figures

Figure 7. Details of the complete tree obtained for the tribe Pseudothelphusini, showing alternative arrangements of the species of Pseudothelphusa. A, Disparithelphusa pecki is the sister taxon of Pseudothelphusa nelsoni and Pseudothelphusa parabelliana. B, Pseudothelphusa dilatata and Pseudothelphusa seiferti are sister species. C, the position of Pseudothelphusa morelosis changes. D, Disparithelphusa pecki and P. parabelliana are sister species.