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Caecidotea chicoensis sp. nov. (Figs 10–13) Material examined: Holotype, male (CNCR 35516), length 9.5 mm, National Park Mineral del Chico, spring behind the visitor center, 20°11’01”N, 98°42’57”W, elev. 2985 m, Municipality Mineral del Chico, Hidalgo, Mexico, 12 December 2018, coll. L. García-Vázquez and M. C. Jordán-Hernández. Paratypes, male (CNCR 35517) length 9.5 mm; same data of collection and collectors as holotype; dissected parts pereiopod I, pereiopod IV, pleopod II; dissected structures for right pleopod drawings I, III, IV and V in the specimen tube. Females present in the same container. Diagnosis. Male body 3 times its width. Head rectangular, width 2.7 length, anterior margin concave; eyes small, oblique oval, length 1.5 width, postmandibular lobes produced. Pleotelson lateral margins parallel, caudomedial lobe subacute produced. Pleopod II protopod ventral surface with cuticular scales on dorsal edge; exopod with ornamentation on ventral surface; endopod medial surface with elongated transverse striations. Uropods irregular, lanceolate. Description. Male (CNCR 35516) 9.5 mm (Fig. 10A); head rectangular, width 2.7 times length, anterior margin concave. Eyes present, oval, dark pigmented, length 0.4 width. Postmandibular lobes produced. Subrectangular pereionites lateral margins straight with setae, as well as on dorsal surface. Pereionite 1 length 1.0 pereionite 2 length; pereionite 1 0.9 pereionite 3 length; pereionites 6–7 with subrectangular margins, posterior narrowing. Antennula flagellum with 11 articles, reaching distal antenna podomere middle, when projecting forward; last four segments with aestetascs in formula 0–1–1–1. Antenna flagellum with 67 articles; proximal article longer than wide, following articles decreasing in length. Pereiopod I (Figs 10B, 11A–B) propodus slender triangular, dactylus outer edge with simple setae as long as palm, irregular inner edge; inner and outer palmar margin with row simple setae; proximal process with 3 robust setae; mesial process acute, exceeding dactylus width. Pereiopods II–III (Fig. 10C – D) similar length. Pereiopod IV (Figs 10E, 11C), propodus with spine in dactylus; dactylus robust; dactylus length 0.5 propodus length, lower margin with five strong spines. Pereiopod V (Fig. 10F), basis similar length to propodus. Pereiopod VI (Fig. 10G) as long as pereiopod VII, basis length similar to carpus length. Pereiopod VII (Fig. 10H) 1.2 body length. Pleopod I (Fig. 12A) as long as pleopod II; protopod subrectangular, proximal margin rounded, length 1.6 width, inner margin with 3 retinacula, distal segment subrectangular, outer margin concave, length 2.6 times width, margins with 10 simple setae. Pleopod II (Fig. 13A–F), protopod subrectangular, distal edge with cuticular scales; exopod base triangular with distal spines; exopod oval, with small cuticular scales, distal margin with 20–25 long plumose setae; slender endopod, as length 4.6 width, 1.1 exopod length 0.8 times protopod length, mesial surface curved, with irregular reticulations, internal and external process prominent; endopod apex with 3 processes: cannula subcylindrical, apex truncated with transverse striations on mesial surface, caudal process present; mesial process subtriangular, striated surface; caudal process robust, subconical, rounded apex, armed with 2–6 cuticular scales directed proximally. Pleopod III (Fig. 12B), exopod oval with distal margin setose, length 1.4 endopod length, width 1.6 endopod width, transverse suture in proximal half, 20 plumose setae on distal margin, external margin with 40 simple setae; endopod short oval, 0.7 exopod length. Pleopod IV (Fig. 12C), exopod length 1.6 width, external margin with 10 proximal setae; endopod length 0.9 exopod length. Pleopod V (Fig. 12D), exopod oval, length 1.9 width, transverse suture not evident; endopod length 0.9, width 0.9 exopod length. Pleotelson (Fig. 12E), as wide as long, lateral margins parallel, rounded with several simple setae, caudomedial lobe produced subacute. Uropods (Fig. 12E), subsquare, length 0.9 pleotelson width, armed with robust setae; endopod irregular, lanceolate, length 1.1 pleotelson length, exopod as long as protopod. Habitat. The specimens of Caecidotea chicoensis sp. nov. were located in a small spring, approximately 1 meter in diameter, located behind the visitor center of Mineral del Chico National Park. The water that emerges from the spring runs through a small channel approximately 50 cm wide; algae growths and anuran larvae were also found. Distribution. Only known from the type locality. Etymology. This species is named after the Mineral del Chico National Park. Remarks. Caecidotea chicoensis sp. nov. can be distinguished from other Mexican species of Caecidotea by the presence of elongated striations on the medial surface of pleopod II endopod., Published as part of García-Vázquez, Leonardo, Pedraza-Lara, Carlos & Rodríguez-Almaraz, Gabino, 2021, Six new epigean species of Caecidotea (Isopoda: Asellidae) distributed along the Trans-Mexican Volcanic Belt in Central Mexico, pp. 45-77 in Zootaxa 4965 (1) on pages 56-61, DOI: 10.11646/zootaxa.4965.1.2, http://zenodo.org/record/4723078