Pseudothelphusa chilapaensis, Madrigal & Villalobos-Hiriart & Álvarez, 2025

Madrigal, Kevin J., Villalobos-Hiriart, José Luis & Álvarez, Fernando, 2025, Integrative taxonomic analysis of the Pseudothelphusa americana de Saussure, 1857 species complex with the description of three new species (Decapoda, Pseudothelphusidae, Pseudothelphusinae), Zootaxa 5659 (1), pp. 1-28 : 14-17

Pseudothelphusa chilapaensis sp. nov.

http://zoobank.org/ 2C9A52D9-6992-41A8-8CCC-BED2810E9FCD

( Figures. 5 , 8 )

Pseudothelphusa (Pseudothelphusa) americana americana – Bott 1968: 40, figs. 1a, 1b.

Pseudothelphusa americana – Villalobos-Hiriart 2005: 127 [not Pseudothelphusa americana de Saussure, 1857 ].

Type material examined. Holotype (herein designated): male (CL 21.73 mm, CW 34.14 mm) ( CNCR 29077 ), Ajolotero River , ~ 5 km SW of Chilapa, municipality of Chilapa de Álvarez, Guerrero, Mexico, 17°34’30.00”N 99°12’24.60”W, 1527 m asl, coll. J.L. Villalobos, A. Celis, O. Vázquez & G. García, 9 June 2000 . Paratypes: 9 males (CL 14.42–21.44 mm, CW 22.29–33.62 mm), 4 females (CL 10.06–19.99 mm, CW 16.10–30.42 mm) ( CNCR 29078 ), same data as holotype .

Description. Carapace slightly convex in dorsal view; surface finely punctuated/reticulated, punctuation concentrated near anterolateral margin, between postfrontal lobes and on frontal border ( Fig. 5B ). Superior frontal border absent; front gently curved downwards; frontal border bilobed, continuous, thick, smooth, central portion with shallow, narrow depression ( Fig. 5A, B ). Postfrontal lobes well marked, slightly elevated; frontal median groove well defined, wide, shallow; cervical grooves notably marked, wider, deeper at proximal end, not reaching anterolateral margin ( Fig. 5B ). Gastric region well defined, convex, slightly higher than branchial region, cardiac region marked by 2 shallow lateral depressions near urogastric region; urogastric sutures Y-shaped, horizontally arranged, slightly inclined, curved at middle. Notch on external orbital angle absent ( Fig. 5B ). Anterolateral margin ornamented with low denticles, most conspicuous on meso-branchial section, decreasing progressively in size towards external angles; posterior margin straight ( Fig. 5B ).

Frontal border straight in frontal view, convex at level of antennular fossae, without widening at lateral angle ( Fig. 5A ). Orbits subrectangular; orbital margin with inferior and lateral borders crenated; inferior border slightly inclined; external orbital angle subacute with lateral notch; internal orbital tooth subtriangular, like grooved plate, well-developed, separated from lateral angle of frontal border, leaving moderately narrow hiatus ( Fig. 5A ). Antennae not separated from front; antennal basal article not covered by lateral angle of frontal border ( Fig. 5A ). Interantennular septum small, sharp, inserted under inferior frontal border. Operculum of antennal gland ovoid, tuft of bristles on external portion. Branchial efferent channel aperture subquadrangular, width/length ratio 1.2. Epistomal tooth at septum level, triangular, downwards directed. Pterygostomial region, epistome pubescent. Third maxillipeds covering buccal cavity, ischium subtrapezoidal, width/length ratio 0.90, gnathal margin ornamented with small subtriangular teeth decreasing in size distally, bristle tuft placed between teeth; merus of third maxilliped with anterolateral border rounded, not extending beyond buccal cavity, width/length ratio 1.21; anterior notch present, shallow; gnathal border gently excavated to permit the palp insertion, inferior portion ornamented with small teeth and long bristles; palp mesially pubescent, denser towards the dactylus; third maxilliped surface punctuated, each punctuation with setae, distributed longitudinally in the gnathal margin; exognath wider at base, ending in acute apex, exognath/ischium length 0.65 ( Fig. 5C ).

Chelipeds asymmetrical; internal border of merus with small tubercules; internal border of carpus with low, wide granules, armed with triangular, acute spine. Major chela with palm surface punctuated; dactylus and fixed finger separated by moderately broad gap; dactylus some widened, faintly curved; cutting borders with low teeth dentated ( Fig. 5D ).

G1 straight, robust, with distal third twisted towards median axis of sternal surface of body. In caudal view, distal third straight; distal crest of caudo-marginal projection higher than lateral crest; distal end of caudal surface with wide, shallow concavity ( Fig. 5G ). Caudal surface of mesial process with basal lobe well-developed, conical, wide at base. In mesial view, caudo-marginal projection with subapical surface of caudal margin slightly excavated; crest of distal lobe smooth, rounded caudally, straight cephalically; distal lobe small, triangular, slightly directed downwards, with acute apex, faintly projected towards mesial side, separated from proximal lobe by wide V-shaped notch; proximal lobe U-shaped, broad, short, length/width 1.66, moderately oblique to principal axis, distal margin rounded ( Fig. 5H ). In cephalic view, distal third moderately tilted laterally; distal and proximal lobes of caudo-marginal projection disposed in same plane, proximal lobe oblique to G1 principal axis, inner surface moderately swollen, with low median carina reaching beyond middle portion ( Fig. 5F ). Mesial process subtrapezoidal, perpendicular to G1 principal axis, ending laterally in triangular subacute spine; superior border straight with long and sinusoidal crest covering two thirds of process reaching inner lobe; inferior border with proximal portion convex, distal portion gently concave, extending to lateral spine; inner lobe subquadrangular, laminar, in contact with inner surface of proximal lobe ( Fig. 5F ). In lateral view, mesial process latero-caudally curved; basal lobe of caudal surface with conical apex ( Fig. 5I ). In distal view, apical cavity U-shaped, of uniform width; central crest of apical cavity moderately high, straight, reaching inner lobe of mesial process; apical spines field deep, in central position, with approximately 17 moderately short spines, disposed in 2 irregular caudo-cephalic rows, cephalic spines partially covered by superior border of mesial process ( Fig. 5E ). Aperture of spermatic channel in caudal position. Mesial process with lateral spine moderately slender at base, curved, directed latero-caudally; basal lobe of caudal surface noticeable, conical, developed ( Fig. 5E ).

Type locality. Ajolotero River (17°34’30.00”N 99°12’24.60”W, 1527 m asl), ~ 5 km SW of Chilapa, municipality of Chilapa de Álvarez, Guerrero, Mexico .

Etymology. The species epithet is taken from the municipality of Chilapa de Álvarez where the species was collected.

Remarks. The G1 of P. chilapaensis sp. nov. is similar to that of P. americana s.s., particularly in mesial view. However, it is possible to recognize certain differences between them: in caudal view, P. chilapaensis sp. nov. has the basal lobe of the caudal surface of the mesial process well-developed, and it is discernible laterally and caudally ( Fig. 5G, I ) (versus basal lobe inconspicuous in P. americana s. s.; Fig. 4G, I ); in cephalic view, the lobes of the caudo-marginal projection are moderately inclined away from the main axis of the gonopod in P. chilapaensis sp. nov. ( Fig. 5F ) (versus straight and parallel to the main axis in P. americana s.s.; Fig.4F ); and in mesial view, the distal crest of the caudo-marginal projection of P. chilapaensis sp. nov. is rounded caudally and straight cephalically, and the proximal lobe is short and broad, its length/width ratio is 1.66, and is moderately oblique to the principal axis, and rounded distally ( Fig. 5H ) (versus the distal crest of the caudo-marginal projection is widely rounded, the proximal lobe is slender and elongated, its length/width ratio is 1.85, and is proximally directed, and acutely curved distally in P. americana s.s.; Fig. 4H ). Additionally, some somatic structures display morphometric differences, e.g., the exognath length/ischium length ratio is 0.65 in P. chilapaensis sp. nov. (versus 0.83 in P. americana s.s).

Bott (1968) revised freshwater crabs that came from Xochitempa near Chilapa, Guerrero. He considered those individuals to belong to Pseudothelphusa (Pseudothelphusa) americana americana without further comments. Villalobos-Hiriart (2005) identified the crabs from Río Ajolotero as a different morphological form of P. americana s.s., but just as Bott (1968), did not make any remarks about them. Our phylogenetic analysis retrieved P. chilapaensis sp. nov. as sister group to P. belliana + P. hoffmanae clade and completely separated from P. americana s. s. populations ( Fig. 2 ). In summary, the molecular, morphological, and geographical evidence presented support the description of P. chilapaensis sp. nov. as a new taxon.

Distribution. Pseudothelphusa chilapaensis sp. nov. was collected from the type locality, Ajolotero River, and at Xochitempa (17°31’36.73”N 99°10’10.47”W; 1900 m asl), near Chilapa, Guerrero, Mexico ( Bott, 1968).

Figures

FIGURE 2. Phylogenetic tree obtained from BI and ML of three concatenated genes (COI, 16S, H3). Posterior Probability (PP) and Bootstrap (B) values above. 50/50 respectively are shown.

FIGURE 4. Pseudothelphusa americana sensu stricto, male, neotype (CL 26.60 mm, CW 40.63 mm) (CNCR 35390).A, frontal view; B, dorsal view; C, ventral view; D, major chela; E, G1 distal view; F, G1 cephalic view; G, G1 caudal view; H, G1 mesial view; I, G1 lateral view. Abbreviations: ASF, apical spine field; BL, basal lobe; DC, distal crest; DL, distal lobe; LC, lateral crest; MP, mesial process; PL, proximal lobe; SCA, spermatic channel aperture. Scale bars: A–D = 5 mm; E–I = 1 mm.

FIGURE 5. Pseudothelphusa chilapaensis sp. nov., holotype (CL 21.73 mm, CW 34.14 mm) (CNCR 29077). A, frontal view; B, dorsal view; C, ventral view; D, major chela; E, G1 distal view; F, G1 cephalic view; G, G1 caudal view; H, G1 mesial view; I, G1 lateral view. Abbreviations: ASF, apical spine field; BL, basal lobe; DC, distal crest; DL, distal lobe; LC, lateral crest; MP, mesial process; PL, proximal lobe; SCA, spermatic channel aperture. Scale bars: A–D = 5 mm; E–I = 1 mm.

FIGURE 8. Map of central Mexico showing the distributions of the four Pseudothelphusa species recognized in this study. Localities: 1, Mixquiahuala; 2, Ventoquipa; 3, Michac; 4, Chignahuapan; 5, Zacatlán de las Manzanas; 6, San Miguel La Presa, Ixtacuixtla; 7, La Ascención Huitzcolotepec; 8, ‘El Ojito’ Spring, Apizaco (P. americana s. s. type locality); 9, Palo Huérfano; 10, Cuahutinchán; 11, Cuauxixtla; 12, San Marcos Necoxtla; 13, Ajolotero River, near Chilapa; 14, Querétaro-state of Mexico. State abbreviations: CMX, Mexico City; GUA, Guanajuato; GRO, Guerrero; HID, Hidalgo; MEX, State of Mexico; MIC, Michoacán; MOR, Morelia; OAX, Oaxaca; PUE, Puebla; QUE, Querétaro; TLA, Tlaxcala; VER, Veracruz.