Caecidotea alvarezi García-Vázquez & Pedraza-Lara & Rodríguez-Almaraz 2021, sp. nov.

Caecidotea alvarezi sp. nov.

(Figs 2–5)

Material examined: Holotype, male (CNCR 35519), length 5.0 mm, shore of the Chapala Lagoon, Jamay, 20°17’07.00”N, 102°42’36.97”W, elev. 1524 m, Municipality of Jamay, Jalisco, Mexico, 19 March 2018, coll. L. García-Vázquez and C. Pedraza-Lara.

Paratypes, male (CNCR 35520), length 4.7 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 2.8 times longer than wide. Head trapezoidal, width 0.6 length, anterior margin straight; eyes 3 times longer than wide, postmandibular lobes not produced. Pleotelson lateral margins parallel, caudomedial lobe produced, broad, rounded. Pleopod II exopod with cuticular scales directed distally, as long as those in medial margin cannula; endopod with flagella, mesial process almost high as cannula. Uropods long as pleotelson length.

Description. Male (CNCR 35519) 5.0 mm (Fig. 2); head width 2.8 length, anterior margin straight. Eyes present, oval, dark pigmented, length 0.6 width. Postmandibular lobes not produced. Subrectangular pereionites lateral margins ornamented with setae, pereionites 1–2 rounded, pereionites 3–5 straight, pereonites 6–7 rounded, posterior angle produced.

Pereionite 1 length 1.1 pereionite 2 length; pereonite 1 0.9 pereionite 3 length; pereionites 6–7 wider, widening in posterior angle.

Antennula flagellum with 10 articles, longer than distal antenna podomere middle; last four segments with aestethascs in formula 1–1–1–0. Antenna flagellum with 50 articles; proximal article wider than long; following articles decreasing in length.

Pereiopod I (Figs 2B, 3A–B) propodus slender, dactylus longer than palm with five simple setae on outer surface, irregular inner edge; palmar margin with row simple setae; proximal process with robust spine length 0.3 mesial process length; mesial process acute, exceeding dactylus width. Pereiopods II–III (Fig. 2C–D) similar length. Pereiopod IV (Figs 2E, 3C–D), propodus with spine in dactylus; dactylus length 0.5 propodus length with 3 spines on lower margin. Pereiopod V (Fig. 2F) basis 1.3 propodus length. Pereiopod VI (Fig. 2G) similar length to pereiopod VII length, basis length 1.4 propodus length. Pereiopod VII (Fig. 2H) 0.5 body length.

Pleopod I (Fig. 4A) length 1.1 pleopod II length; protopod trapezoidal, proximal margin straight, length 1.5 width, inner margin with 5 retinacula, distal segment subrectangular, outer margin concave, length 2.3 width, margins with 20 simple setae.

Pleopod II (Fig. 5A–F), protopod subrectangular, proximal edge rounded; exopod oval, in dorsal view with two vertical rows cuticular scales adjacent to inner margin, distal margin with 20 short plumose setae; slender endopod, as long as 3.8 width, similar to exopod 0.7 protopod length, curved mesial surface with flagella, internal and external process prominent, with suture close to base; endopod apex with 3 processes: cannula short, shaped as ribbed blade, not closed, tip truncated rounded, almost reaching apex caudal process, ventral groove present, extending proximally from base to cannula more than 3.0 its length; mesial process evident, with transverse grooves on surface; caudal process robust, conical, rounded apex, armed on subapical dorsal surface with 7–17 cuticular scales directed proximally.

Pleopod III (Fig. 4B), exopod oval with distal margin setose, length 1.1 endopod length, width 1.6 endopod width, transverse suture in proximal half, 15 plumose setae on distal margin, external margin with 6 simple setae; endopod short oval, 0.9 exopod length.

Pleopod IV (Fig. 4C), exopod as long as 1.7 width, with pronounced notch, on outer margin, close to pleopod joint; endopod 0.9 exopod length.

Pleopod V (Fig. 4D), exopod oval, as long as 1.8 width; transverse suture not obvious; endopod length 0.9 exopod length, width 0.7 exopod width.

Pleotelson (Fig. 4E), subsquare, width 1.1 length, lateral margins parallel, with simple setae, caudomedial lobe broad rounded.

Uropods (Fig. 4F), length equal to pleotelson length, armed with robust setae; length 0.5 endopod length; endopod linear, length 0.8 protopod length, exopod length 1.1 protopod length.

Habitat. This species was collected on the shoreline of the Chapala lagoon within the roots of the water lily Eichornia crassipes, along with other crustaceans (e.g., crayfish of the genus Cambarellus and amphipods of the genus Hyalella).

Distribution. Only known from the type locality.

Etymology. This species is named in honor to Dr. Fernando Alvarez, curator of the National Crustacean Collection, in recognition to his career in the study of Mexican crustaceans.

Remarks. C. alvarezi sp. nov. is similar to the species C. williamsi Escobar-Briones & Alcocer, 2002 from Laguna de Alchichica, Puebla. The two species, however, can be distinguished by the number of retinacula in pleopod I (3 in C. williamsi and 5 in C. alvarezi sp. nov.) and the shape of pereiopod I. C. williamsi has only mesial process, while C. alvarezi sp. nov. has both mesial and proximal processes.