Mokayathelphusa angelsotoi Moreno, Villalobos & Álvarez, 2022

Moreno-Juárez, Eric G., Villalobos, José Luis & Álvarez, Fernando, 2022, Two new genera and one new species of freshwater crabs of the subfamily Pseudothelphusinae (Decapoda: Brachyura: Pseudothelphusidae) from southwestern Mexico, Zootaxa 5200 (1), pp. 24-36 : 28-29

Mokayathelphusa angelsotoi Moreno, Villalobos & Álvarez n. sp.

( Figs. 3 , 4 )

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Type material. Holotype: CNCR 34843 , ♂, CL 14.9 mm, CW 23.1 mm; tributary of Río Negro , near the town of Santa María Chimalapa, 16°54’41”N, 94°42’21”W; 144 m asl, Municipality of Santa María Chimalapa, Oaxaca, Mexico, coll. A. Soto, 20 July 2018.

Description. Surface of carapace flat, smooth, except finely punctate branchial region. Cardiac, mesogastric, urogastric and branchial regions, discernible. Postfrontal area swollen, curved anteriorly to reach poorly defined superior frontal margin; postfrontal lobes low, separated by narrow, shallow median groove, ending anteriorly in median notch dividing superior frontal border. Cervical groove straight, narrow, well-marked, short, not reaching anterolateral margin. Lateral margin with 30 denticles and two shallow notches, anterior notch behind external angle of orbit, posterior notch at level of cervical groove ( Fig. 4a ). In frontal view, front, antennules, proepistome, epistome, and merus of third maxillipeds with minute dark spots; superior frontal margin marked by acute frontal bend of carapace, inclined towards median groove, with small granules, divided by V-shaped median notch; inferior frontal margin sinuous, with blunt granules, adjacent portion to antennular cavity higher than rest; interantennular septum concealed by inferior frontal margin. Antennules and antennular fossae visible, fossae wider in middle. Antennal peduncle filling orbital hiatus.Orbital margin well defined, internal surfaces of ocular cavities with scattered dark spots and short setae; inner tooth slender, elongate, concave longitudinally, superior margin subtriangular. Opercular plate of antennal gland ovoid. Superior margin of proepistome sharp in middle, oval-shaped at lateral ends. Epistome setose, surrounding buccal cavity; laterally with rounded granules; epistomal tooth triangular, apex directed anteriorly at same level of interantennular septum, between palps of third maxillipeds when closing buccal cavity. Opening of efferent branchial channel subquadrate, superior margin curved, ratio width/length 1.25.

Third maxilliped with ischium trapezoidal, 1.33 times wider than long; merus narrower than ischium, anterior margin widely rounded with shallow, rounded notch next to insertion of palp; ratio exopod/ischium length 0.65 ( Fig. 4b ).

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, swollen; fingers gaping, curved inwards distally, cutting edges with triangular teeth ( Fig. 4b ). Dactylus narrow, dorsal surface with longitudinal rows of small pits, cutting edge with two proximal triangular teeth, remaining edge with alternate small and big teeth, ending in curved acute point. Propodus cutting edge with two small proximal teeth, six medial triangular and acute ones, seventh smallest, final point acute, incurved.

G1 slender, with torsion throughout its length, distal half curved mesially making apical cavity visible in mesocephalic position. In mesial view ( Fig. 3a ), principal axis twisted counterclockwise, distal crest of caudal surface (Cdc) cephalically oriented, projected mesially; distal portion of caudo-marginal projection directed cephalad, with distal lobe (Dl) as a strong spine with flat distal surface, delimited by well marked external crest (Ecdl); medial lobe (Ml) not visible; proximal lobe (Pl) partially evident in proximal half, as curved sheet, with subacute end; distal crest of apical cavity ornamented with acute, hooked spinules. In caudal view ( Fig. 3b ), principal axis with distal half twisted, mesially inclined; medial portion with curved, sharp caudal edge (Ce), lateral surface with sharp rib-like border (Le); mesial process (Mp) as laminate rectangular plate, lateral margin raised, produced into irregular crest (Lbmp), armed with acute teeth; distal crest of lateral surface (Ldc) widely rounded. In lateral view ( Fig. 3c ), distal half of gonopod straight, surface smooth, Ldc rounded; Lbmp thin, armed with nine irregular teeth, distally forming right angle with superior border; lobes of caudo-marginal projection partially visible, Dl and Ml conical, acute, Pl triangular. In cephalic view ( Fig. 3d ), distal half inclined mesially; lobes of caudo-marginal projection evident, Dl and Ml conical, acute, latero-cephalically directed, distal one moderately stouter; Pl as curved sheet, distal end slender, rounded; mesial process as thin plate with toothed lateral border (Lbmp); distal portion forming right angle with superior border (Dbmp); apical cavity U-shaped, mesial distal crest (Mdc) with row of acute, hooked spinules, field of apical spines adjacent to internal lateral surface with several chitinized setae, aperture of spermatic channel on caudal position, distal crest of lateral surface projecting distally. In distal view ( Fig. 3e ), apical portion evidently curved cephalad, apical cavity (Ac) barely visible; Ldc smooth laterally, mesially armed with short spinules; distal lobe of caudo-marginal projection conical, slender, acute; mesial process partially noticeable. Apical cavity only visible distally in meso-cephalic position ( Fig. 3f ), U-shaped, aperture on cephalic surface, closed by internal angle of mesial process (Imp); field of spines (Sf) adjacent to lateral surface, with 10 long, conical and slender corneous setae, and 20 shorter conical tubercles scattered on caudal portion of cavity; aperture of spermatic pore (Sp) in caudal position, with spinules on caudal internal surface; distal crest of mesial surface (Mdc) armed with slender spinules. Dl and Ml of caudo-marginal projection, almost totally visible, conical, subacute, fused at base, directed cephalad.

Distribution. Known only from the type locality.

Type locality. Stream tributary of Río Negro (16°54’41”N, 94°42’21”W; 144 m asl), Municipality of Santa María Chimalapa, Oaxaca, Mexico .

Etymology. This species is named after Ángel Fernando Soto Pozos, enthusiastic herpetologist interested in the biodiversity of the Chimalapas region, and collector of the type specimen.

Remarks. The G1 morphology of Mokayathelphusa angelsotoi sp. nov., is unique among the members of the subfamily Pseudothelphusinae . The new species is genetically related to Disparithelphusa pecki Smalley & Adkison, 1984 . Both species present a trilobed caudo-marginal projection, the two short distal lobes and the elongated proximal one. However, the shape, arrangement and orientation of these lobes are completely different. Other apical elements such as the mesial process, and the form and ornamentation of apical cavity, also show differences.

Geographically, Diparithelphusa pecki occurs in northern Oaxaca, in the Sierra de Juárez near the town of Tuxtepec, whereas Mokayathelphusa angelsotoi n. sp. occurs in the Chimalapas region about 190 km to the southeast ( Fig. 1 ). Genetically, both species are clearly different as seen in their phylogenetic placement ( Fig. 2 ).

Figures

FIGURE 1. Distribution of monotypic genera in Mexico, subfamilies Pseudothelphusinae and Raddausinae.

FIGURE 2. Consensus tree resulting from ML and BI analyzes of the concatenated matrix (COX 1, 16S and H3) from the genus of the Pseudothelphusinae subfamily.

FIGURE 3. Mokayathelphusa angelsotoi sp. nov., holotype G1 views: a) mesial, b) caudal, c) lateral, d) cephalic, e) distal, f) apical cavity. Abbreviations: Ac) apical cavity; Cdc) caudal distal crest; Ce) caudal edge; Dl) distal lobe of the caudo-marginal projection; Dbmp) distal border of the mesial process; Ecdl) external crest of the distal lobe; Imp) internal angle of the mesial process; Lbmp) lateral border of the mesial process; Ldc) lateral distal border; Le) Lateral edge; Mdc) mesial distal crest; Ml) mesial lobe of the caudo-marginal projection; Mp) mesial process; Ms) Marginal suture; Sf) spine field; Sp) spermatic pore. Scales as broad lines a-e: 1mm; f: 0.5 mm.

FIGURE 4. Mokayathelphusa angelsotoi sp. nov. a) carapace dorsal view, b) carapace frontal view, c) chela, d) carapace ventral view, abdomen removed.