Pseudothelphusa ixtapan, Ojeda-Escoto, Juan Carlos, Villalobos, José Luis & Álvarez, Fernando, 2017

Ojeda-Escoto, Juan Carlos, Villalobos, José Luis & Álvarez, Fernando, 2017, Three new species of freshwater crabs of the genus Pseudothelphusa (De Saussure, 1857) (Crustacea: Decapoda: Pseudothelphusidae) from Mexico, Zootaxa 4216 (6), pp. 559-571 : 564-566

Pseudothelphusa ixtapan n. sp.

( Figs. 4 , 5 )

Pseudothelphusa (Pseudothelphusa) dugesi belliana Rodríguez & Smalley, 1969: 81 , fig. 13, pl. 9. Pseudothelphusa belliana Rodríguez, 1982: 135 , fig. 88.

Pseudothelphusa (Pseudothelphusa) belliana form Ixtapan de la Panocha, Villalobos, 2005:248, pl. 18.

Type material. Male holotype, cl 24.3 mm, cb 40.1 mm; Aguiagua River near Ixtapan de la Panocha (18°54' N, 100°09' W; 1,018 m asl), San Miguel Ixtapan , Municipality of Tejupilco, state of Mexico, Mexico; 25 April 1961 ; coll. anonymous; CNCR 343. This individual was considered as Pseudothelphusa dugesi belliana and included as part of the material examined by Rodríguez & Smalley, 1969: 81, pl. 9 catalog number UNAM 4 25 61.

Description. Dorsal surface of carapace smooth, central portion flat, puntacted ( Fig. 4 A). Frontal portion lacking superior frontal border, curved downward reaching inferior frontal border, partially visible dorsally ( Fig. 4 A, D). Front smooth, moderately bilobed, inferior frontal border slightly projected, sinuous, with evident middle concavity, slight convexity at level of antennular fossae ( Fig. 4 D). Postfrontal lobes well formed with shallow anterior depression. Frontal portion of carapace anterior to postfrontal lobes convex. Median frontal groove shallow, well-marked, dividing front anteriorly reaching inferior frontal border; posteriorly separating postfrontal lobes, becoming obsolete little after. Cervical grooves well marked, wide, straight, not reaching anterolateral margin; posterior end curved. Regions moderately indicated, gastric, branchial swollen; cardiac, intestinal depressed ( Fig. 4 A). Anterolateral margin moderately prominent in lateral view, serrated, with 19 blunt tubercles on left side, 23 on right side, from cervical groove to mid branchial region; area between orbit, cervical groove depressed with fused granules. Posterior margin of carapace straight ( Fig. 4 A).

External angle of orbit faintly developed, with shallow basal notch; internal angle extending into interior of orbital cavity as moderate keel ( Fig. 4 D). Basal article of antennal peduncle separated from inferior frontal margin by narrow hiatus. In frontal view, antennules, antennular fossae, interantennular septum concealed by front ( Fig. 4 D); internal margin of second antennular article with small distal projection; ventrally antennular fossae wider in middle, inferior frontal margin slightly sinuous. Opercular plate of antennal gland ovoidal, with small central constriction, tuft of setae on external third. Epistome, portions surrounding buccal cavity with dense patch of setae; lateral portions with rounded granules; epistomal tooth triangular, apex directed downward at same level of interantennular septum ( Fig. 4 D). Opening of efferent branchial channel subquadrangular, ratio wide/length 1.36. Ischium of third maxilliped trapezoidal, slightly longer than wide; merus narrower than ischium, superior margin rounded, with shallow, rounded notch before the insertion of palp; ratio exopod/ischium 0.67 ( Fig. 4 C).

Chelipeds asymmetrical. Merus of larger cheliped with row of blunt tubercles along internal margin, carpus with triangular spine on internal margin. Chela with internal surface smooth, globose; fingers gaping, curved inward distally, with low, triangular teeth on cutting edges ( Fig. 4 B). Dactylus rather narrow, widely curved, dorsally ornamented with several longitudinal rows of small pits, black granules.

Male gonopod moderately strong. In mesial view, distal crest of caudomarginal projection curved; distal lobe as triangular subacute tooth, separated from proximal lobe by U-shaped notch, with apex not reaching beyond cephalic margin ( Fig. 5 A). Proximal lobe longer than wide, oval-shaped, proximally directed; cephalic margin curved ( Fig. 5 A). In cephalic view, distal lobe of caudo-marginal projection directed cephalically, aligned with proximal lobe; internal border close to inner expansion of mesial process. Proximal lobe slightly oblique with respect to longitudinal axis of gonopod; distal half of internal surface swollen with ill-defined border; cephalic margin straight ( Fig. 5 B). Mesial process as rectangular laminar expansion, distal margin perpendicular to longitudinal axis of gonopod, lateral margin with acute median tooth, series of small acute teeth on proximal angle ( Fig. 5 B). Superior margin almost straight, ending internally in rectangular inner expansion, rounded, closing apical cavity; same margin developing into central crest in apical cavity, delimiting field of spines. Inferior margin widely rounded. In lateral, mesial views, apical cavity oriented caudo-cephalically ( Fig. 5 A, C). In caudal view, distal third straight, tilted mesially, distal crest concave ( Fig. 5 D). In apical view, cavity U-shaped, opening of sperm channel in caudal position; field of spines wide, close to lateral crest, more than 60 terminal pore setae, some organized in caudo-cephalic rows; internally cavity armed with hook-shaped spinules along mesial, caudal surfaces ( Fig. 5 E).

Geographical distribution. Only known from the type locality.

Etymology. The specific epithet is the name of the type locality, Ixtapan , in the state of Mexico; it is used as a noun in apposition.

Remarks. Based on the morphology of the first gonopod, Pseudothelphusa ixtapan n. sp. is close to those species of Pseudothelphusa with a subrectangular mesial process, like P. dilatata Rathbun, 1898 , P. digueti Rathbun, 1898 , and P. morelosis Pretzmann, 1968 . The differences among these species are in the ornamentation of the mesial process, P. ixtapan n. sp. has only one lateral strong tooth and the inferior border is armed with a row of five acute spinules. In P. dilatata , P. digueti and P. morelosis the lateral margin of the mesial process has more than one spiniform tooth; the inferior border is smooth in P. morelosis and P. digueti , with denticles in P. dilatata .

The new species is distributed in the same area where P. mexicana and P. granatensis occur, in the border region between the states of Guerrero and Mexico. Pseudothelphusa morelosis , is another related species with a geographically close distribution in the Balsas River basin.

Figures

FIGURE 4. Pseudothelphusa ixtapan n. sp., male holotype, CNCR 343: A, dorsal view; B, major chela; C, third maxillipeds; D, frontal view of carapace.

FIGURE 5. Pseudothelphusa ixtapan n. sp., male holotype CNCR 343, left first gonopod: A, mesial view; B, cephalic view; C, lateral view; D, caudal view; E, apical view; F, total cephalic view. Abbreviations: ac, apex cavity; cmp, caudo-marginal projection; mp, mesial process; ms, marginal suture; osc, opening of sperm channel.