Pseudothelphusa acahuizotla, 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 : 561-564

Pseudothelphusa acahuizotla n. sp.

( Figs. 2 , 3 )

Type material. Male holotype, cl 22.0 mm, cb 35.8 mm; small stream in Acahuizotla (17°21'38" N, 99°28'02" W; 820 m asl), Municipality of Chilpancingo de los Bravo, state of Guerrero, Mexico; 26 July 2014; coll. S.M. Martínez-Zam; CNCR 31708 .

Description. Dorsal surface of carapace flat, punctate, with low tubercles on area behind orbits, adjacent to anterolateral margin at branchial region ( Fig. 2 A). Gastric region inflated, anterior portion slightly curving to reach superior frontal border, marked by acute frontal bend of carapace, inclined towards median groove, with low, rounded tubercles. Front vertically deflexed, smooth, bilobed ( Fig. 2 D); inferior frontal border visible in dorsal view; ventrally slightly projected, sinuous, with evident middle concavity, slight convexity at antennular fossae level. Postfrontal lobes well formed, without anterior depression ( Fig. 2 D). Frontal portion between superior frontal border and postfrontal lobes flat. Median frontal groove narrow, deep, anteriorly finished in V-shaped notch, dividing superior frontal border; posteriorly separating postfrontal lobes, becoming obsolete little after. Dorsal area behind orbits concave. Cervical grooves well marked, wide, curved, ending before reaching anterolateral margin. Regions moderately indicated, gastric, branchial swollen, cardiac, intestinal depressed. Anterolateral margin prominent in lateral view, serrated, with subacute granules from cervical groove to middle portion of branchial region; area between orbit and cervical grove with 8–10 granules. Posterior margin of carapace straight ( Fig. 2 A).

Orbits with external angle faintly developed, granulated, with rounded basal notch; internal angle with high border. Basal article of antenna separated from anterior frontal margin by narrow hiatus. In frontal view, antennules, antennular fossae partially visible, fossae wider in middle; interantennular septum partially covered by inferior surface of frontal border ( Fig. 2 D). Opercular plate of antennal gland ovoid, with small middle constriction, tuft of setae on external third. Epistome, portions surrounding buccal cavity densely setose; laterally with rounded granules; epistomal tooth triangular, apex directed downwards at same level of interantennular septum, between palps of third maxillipeds when closing buccal cavity ( Fig. 2 D). Opening of efferent branchial channel subquadrate, ratio width/length 1.26. Third maxilliped with ischium trapezoidal, slightly longer than wide; merus narrower than ischium, anterior margin widely rounded without shallow, rounded notch before insertion of palp; ratio exopod/ischium 0.75 ( Fig. 2 C).

Chelipeds asymmetrical. Merus of larger cheliped with row of blunt tubercles along internal margin, carpus with strong triangular spine on internal margin. Chela with internal surface smooth, globose; fingers gaping, curved inwards distally, with low, triangular teeth on cutting edges ( Fig. 2 B). Dactylus rather narrow, dorsal surface with longitudinal rows of small pits.

Male gonopod robust. In mesial view, distal crest of caudomarginal projection moderately curved at same level of lateral crest ( Fig. 3 A). Distal lobe of caudomarginal projection ending as acute, triangular tooth, rising from superior angle of proximal lobe, separated by narrow V-shaped notch; apex not reaching cephalic margin. Proximal lobe of caudomarginal projection longer than wide, subtriangular, wider distally, cephalo-proximally directed; cephalic margin curved. In cephalic view ( Fig 3 B), distal lobe of caudomarginal projection oriented cephalically, at same level as proximal lobe; internal surface flat. Proximal lobe of caudomarginal projection parallel to principal axis of gonopod. Mesial process approximately trapezoidal, wider section perpendicular to longitudinal axis of gonopod; distolateral angle with acute spine, caudo-laterally directed. Superior margin rounded, reaching internal angle forming subtriangular expansion closing apical cavity cephalically, in contact with internal surface of caudomarginal projection; same margin developing into central crest inside apical cavity, delimitng field of spines. Lateral border slightly concave, inferior angle rounded. In lateral view ( Fig. 3 C), lateral crest rounded, lateral spine, spine on caudal surface of mesial process visible, middle constriction on lateral surface of principal axis, strongly marked. In caudal view ( Fig. 3 D), distal third of gonopod tilted mesially, caudal crest concave, caudal surface of mesial process armed with well-formed central conical spine. In apical view ( Fig 3 E), apical cavity Ushaped, with opening of sperm channel in caudal position; field of spines wide, close to lateral crest, armed with 20–24 terminal pore setae, caudo-cephalically oriented.

Geographical distribution. Only known from the type locality.

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

Remarks. Regarding the external morphology, Pseudothelphusa acahuizotla is similar to P. belliana Rathbun, 1898 , described from Chautipan, Guerrero; both species have a flat and punctate carapace with round granules on the frontal and branchial surfaces; the front is vertical with a well-marked superior frontal border bearing low, rounded tubercles. Pseudothelphusa acahuizotla n. sp. differs from P. belliana in having the dorsal surface of the carapace smooth, without black and short bristles on the posterolateral regions, and in the following characters of the male gonopod: the size and form of the distal lobe of the caudomarginal projection which is small and triangular, separated from the proximal lobe by a V-shaped narrow notch; and by the shape of the mesial process which is approximately trapezoidal with the lateral spine at the level of the superior margin and in the form of the inferior margin; caudal surface of mesial process with an elongated and rounded spine. Pseudothelphusa belliana ( Rathbun, 1898: 515, fig. 4), has a male gonopod with a distal lobe of the caudomarginal projection slender and separated from the mesial process by a narrow incision; the mesial process is subtriangular, and the superior margin is widely curved; the lateral spine is located on the distal half of the lateral margin; below the spine the lateral margin is straight, and continues proximally to end in the principal axis of the gonopod without forming an inferior margin; the caudal surface of the mesial process has a conical tubercle.

The new species is distributed in southeastern Guerrero, close to P. belliana and P. hoffmannae , all occurring in the Papagayo River basin, where P. galloi , P. nelsoni and P. guerreroensis are also distributed. With the description of P. acahuizotla n. sp. the number of recognized species in the state increases to eight.

Figures

FIGURE 2. Pseudothelphusa acahuizotla n. sp., male holotype, CNCR 31708: A, dorsal view; B, major chela; C, third maxillipeds; D, frontal view of carapace.

FIGURE 3. Pseudothelphusa acahuizotla n. sp., male holotype CNCR 31708, 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, caudomarginal projection; mp, mesial process; ms, marginal suture; tps, terminal pore setae.