Tehuana ayotzintepecensis, Moreno-Juárez & Villalobos & Álvarez, 2022

Moreno-Juarez, Eric G., Villalobos, Jose Luis & Alvarez, Fernando, 2022, Revision of the freshwater crabs of the genus Tehuana Rodriguez & Smalley in Smalley 1970 (Decapoda, Pseudothelphusidae), with the descriptions of two new species, ZooKeys 1117, pp. 1-35 : 1

Tehuana ayotzintepecensis sp. nov.

Figs 4 , 5

Type material.

Holotype: Mexico - Oaxaca • 1 ♂, CL 42.6 mm, CW 67.3 mm; Municipality of Ayotzintepec, Cajone River, south of Ayotzintepec town, stream tributary of Cajone River; 17°39'46"N, 96°07'51"W; alt. 128 m; 5 Mar. 2018; J.L. Villalobos, I.A. Toledano, E.G. Moreno leg; CNCR 34628. Paratype: 1 ♂, CL 43.4 mm, CW 67.4 mm; same as for holotype; CNCR 36323.

Additional material examined.

Mexico - Oaxaca • 2 ♂, CL 26.5-28.2 mm, CW 40.6-42.4 mm; same data as for holotype; CNCR 36324 .

Description.

Carapace with dorsal surface flat, finely punctate, with small black granulations on frontal and anterolateral areas; gastric and branchial regions little inflated; postfrontal portion lightly depressed, almost horizontal, reaching anteriorly superior frontal border. Postfrontal lobes low, but evident, delimited anteriorly by shallow depressions, separated by narrow and deep median groove. Gastric pits deep, wide. Cardiac region discernible. Cervical groove shallow, curved, deep posteriorly, straight anteriorly, becoming obsolete near anterolateral margin, forming shallow notch. Anterolateral margin prominent, armed with 22-24 rounded granules of similar size; granulated between orbit and cervical groove, shallow notch next to orbit. Posterior margin straight (Fig. 4A ). In frontal view, superior frontal border straight, formed by low tubercles, divided by deep, V-shaped median notch, external angle internally projected almost touching internal orbital tooth; inferior frontal border thin, granulated, sinuous, more projected than superior one (Fig. 4B ). Orbits with external angle slightly granulated, with deep basal notch; internal orbital tooth triangular, well developed, extending to interior of orbit floor as high keel. Basal article of antennal peduncle separated from front by orbital hiatus. Antennules and antennular fossae partially visible, slightly widening in middle portion by an undulation of inferior frontal border; interantennular septum concealed by inferior frontal border. Operculum of antennal gland as ovoidal, flat plate, with middle constriction and tuft of short bristles on lateral third. Epistome devoid of setae; pterygostomian region with low granules; epistomal tooth triangular, directed downwards. Opening of efferent branchial channel subrectangular, longer than wide, width/length ratio 0.68. Third maxilliped with trapezoidal ischium, slightly longer than wide; merus anterior margin rounded with shallow rounded notch in palp articulation; ratio exopod/ischium length 0.70.

Chelipeds distinctly heterochelous in males, subequal size in females. Major chela right, merus subtriangular in cross section, superior margin rounded with short transversal rows of low granules; lower inner margin with longitudinal row of conical tubercles increasing in size distally. Carpus proximal half with row of small conical tubercles, distal with scattered tubercles, ending in short acute spine, median spine obtuse. Fingers moderately gaping, punctate, cutting margins with rounded teeth; fixed finger with row of variable sized subtriangular teeth, median ones larger; tips slightly crossing when closed. Palm slightly swollen (length/width ratio 1.34), inner surface smooth, rest of palm with scattered black granules (Fig. 4C ). Dactylus moderately arched, slightly longer than palm (dactylus/palm ratio 1.05).

G1 slender, proximal half cylindrical, becoming compressed distally, meso-distal lobe conical, well developed; principal axis with medial constriction on lateral surface, twisted mesially. In mesial view (Fig. 5B ), distal half inclined towards cephalic surface. Caudo-marginal projection with distal lobe well developed, subrectangular with cephalic margin rounded, separated from proximal lobe by an incision; proximal lobe well developed, ax-shaped, 1.24 as higher than long. Meso-distal lobe arise from caudal corner of mesial surface, well developed, conical, with rounded apex. In caudal view (Fig. 5C ), distal third straight, apical cavity distally directed, caudal surface ending distally in wide, shallow concavity. Caudo-marginal projection distal crest of mesial surface higher than lateral one. Meso-distal lobe well developed, conical, apex rounded. Mesial process reduced, spoon shaped, only partially visible. In cephalic view (Fig. 5A ), mesial process reduced, with the distal surface excavated, transversal to principal axis of G1, without spine on lateral margin, laying over carina of inner surface of proximal lobe of caudo-marginal projection; cephalic border bilobed, internal lobe pyramidal, rounded not touching internal face of caudo-marginal projection distal lobe, lateral lobe rounded, subcylindrical, projected anteriorly more than internal one. Field of apical setae visible, cephalo-caudally elongated, setae brownish, shorter than distal crest of lateral surface. Caudo-marginal projection lobes cephalically directed, separated, distal one slightly curved mesially; proximal one oval shaped, lateromesially inclined; carina of inner surface not visible. Distal crest of lateral surface sharp, with some tufts of short setae; subdistal circular scar on lateral face of principal axis partially visible. In lateral view (Fig. 5D ), distal half inclined cephalically. Caudo-marginal projection with the distal lobe partially visible, separated from the proximal lobe by incision, as long as lobe; inner surface of proximal lobe with semicircular strong carina, which extends over basal third of proximal surface. Mesial process lateral lobe subcylindrical, superior surface excavated, lateral border smooth, developing proximally rounded margin ending in subcircular scar. In distal view (Fig. 5E ), apical cavity U-shaped, opening cephalically. Field of apical setae delimited by central crest and internal surface of lateral surface; 20-60 apical setae; aperture of spermatic channel in caudal position; central crest ending cephalically in acute, triangular internal lobe of mesial process, close to internal surface of distal lobe of caudo-marginal projection. Mesial process with distal surface excavated, as an anterior continuation of the field of setae, raised border delimit the lateral and internal lobes. Meso-distal lobe well developed, conical, apex rounded.

Distribution.

Only known from the type locality in northern Oaxaca, Mexico.

Etymology.

The specific epithet is taken from the town where the specimens were collected: near town of Ayotzintepec. The word is Náhuatl “Ayotlzin-tepec”, and means "hill of the little turtles" ("en el cerro de las tortuguitas" in Spanish).

Remarks.

Tehuana ayotzintepec sp. nov. has the typical morphology of the species distributed throughout the Isthmus of Tehuantepec, with a reduced mesial process, cylindrical or spoon shaped, in a transversal position relative to the G1 principal axis and laying over the proximal lobe of the caudo-marginal projection. These characters, make the new species similar to T. complanata , T. jacatepecensis , and T. lamellifrons ; however, in T. ayotzintepecensis sp. nov. the two lobes of the caudo-marginal projection are of the same length in mesial view, the proximal one has a subacute inner angle and the distal one is completely rounded. Geographically, T. ayotzintepecensis sp. nov. and T. jacatepecensis occur in the same general area along the Gulf of Mexico versant of the Sierra de Juárez in northern Oaxaca. In contrast, T. lamellifrons is distributed along the Pacific versant of the Sierra Madre Occidental in southern Oaxaca, and T. complanata occurs in central Veracruz (Fig. 1 ). The phylogenetic tree is consistent with the morphological similarity as it shows a close relationship between the four species (Fig. 3 ).

Figures

Figure 1. Distribution of the species of the genus Tehuana in southeastern Mexico.

Figure 3. Phylogenetic tree obtained for the genus Tehuana based on the concatenated analysis of three genes (H 3, 16 S, COI), using maximum likelihood and Bayesian inference. Branch supports values are posterior probability / bootstrap. Only clades with branch support above 50 % indicated. Clades a, b, and c are labelled for discussion purposes.

Figure 4. Tehuana ayotzintepecensis sp. nov., male holotype A total dorsal view B frontal view of carapace C left chela. Scale bars: 4 cm (A); 2 cm (B, C).

Figure 5. Tehuana ayotzintepecensis sp. nov., left G 1 of male holotype A cephalic view B mesial view C caudal view D lateral view E distal view. Abbreviations: dl, distal lobe; ic, interal carena of the proximal lobe; imp, internal angle of the mesial process; ldc, lateral distal crest; mc, middle constriction; mdc, mesial distal crest; mdl, meso-distal lobe; mp, mesial process; ms, marginal suture; pl, proximal lobe; sf, spine field; sp, spermatic pore. Scale bars: 1 mm (A-D), 0.5 mm (E).