Caecidotea camaxtli, García-Vázquez & Rodríguez-Almaraz & Pedraza-Lara, 2019

García-Vázquez, Leonardo, Rodríguez-Almaraz, Gabino & Pedraza-Lara, Carlos, 2019, Caecidotea camaxtli (Isopoda: Asellidae) a new species from the Tlaxcala valley, Mexico, Zootaxa 4624 (3), pp. 377-386: 378-384

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Caecidotea camaxtli

sp. nov.

Caecidotea camaxtli   sp. nov.

Figs 1–5 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5

Material examined. Holotype, male ( CNCR 35080), body length 13.5 mm, Laguna El Ojito , San Luis Apizaquito, Municipality of Apizaco, Tlaxcala, Mexico, water channel adjacent to main access road to the reservoir below bridge, 19°26’00’’N, 98°06’00’’W, 2 April 2017, coll. L. García-Vázquez, J. García and S. Martínez. GoogleMaps  

Paratypes, male ( CNCR 35081; dissected parts of pereopod I, pleopod II and the left genital papillae, CNCR 35084; dissected structures for line drawings of left pleopods I, III, IV and V in the specimen’s tube), body length 13 mm. Female ( CNCR 35082), body length 6.4 mm   . 15 males and 15 females ( CNCR 35083)   . 10 males and 10 females (FCB-UANL-C440-08177), all with the same data as the holotype GoogleMaps   .

Diagnosis. Head anterior margin concave, length approximately 2.0 times width; post-mandibular lobes not produced. Pleotelson lateral margins parallel, caudal lobe rounded. Pleopod II exopodite ovate, as long as endopodite; endopodite tip with three processes, caudal process with cuticular scales. Uropod endopodite wide, lanceolate.

Description. Male (CNCR 35080) 13.5 mm ( Fig. 1A, B View FIGURE 1 ); pleotelson with setae as long as antennular article 1. Head width 2.0 times length, anterior margin concave. Eyes present, pigmented, 1.9 times long as wide. Lateral margins with several setae. Post-mandibular lobes not produced. Pereonites lateral margins subrectangular with several setae of same length that first antennular article on lower and upper edges.

Pereonite 1 1.5 length pereonite 2–3 length; pereonites 6 and 7 slightly wider; pereonites 4–7 widest, lateral margin subrectangular, narrowing posteriorly. Genital papillae tube-like ventrally on pereonite 7 and pleonite 1 ( Fig. 3F, G View FIGURE 3 ) with 1–3 small spines on margin, located in posterior ventral margin of last thoracic segment.

Antennula flagellum with 10 articles on both sides, reaching distal border of the last segment peduncle antennal when projected forward; penultimate segments with aestetascs in formula 1–0–1–1. Antenna flagellum with 77 articles; proximal article longer than wide; following articles decreasing in length.

Pereopod I ( Figs 2A View FIGURE 2 , 3A View FIGURE 3 ) dactylus length 1.3 times length of palm, internal border with distinct serration distally before claw; palmar margin with rounded protuberance on joint of dactylus; mesial and distal process with rows of simple setae on both lateral edges. Pereopods II–III not dimorphic subequal in lengths ( Fig. 2B, C View FIGURE 2 ). Pereopod IV ( Fig. 2D View FIGURE 2 ) dimorphic, dactylus length near propodus length, dactylus with row of three strong spines. Pereopod V ( Fig. 3E View FIGURE 3 ) propodus subequal to carpus length. Pereopod VI ( Fig. 2F View FIGURE 2 ) similar length to pereopod VII, propodus similar length to carpus; merus with subcircular projection on midpoint of external margin. Pereopod VII ( Fig. 2G View FIGURE 2 ) length 2.9 times body length; merus with carina at midpoint of lower margin.

Pleotelson width 1.2 times length, lateral margins parallel, with several simple setae, caudomedial lobe rounded.

Pleopod I length 1.3 times pleopod II length; protopodite subtriangular, proximal margin rounded, length 1.7 times width, internal margin with 4–6 coupling hooks, distal segment subrectangular, external margin concave, length 1.8 width, length subequal to proximal article length, distal margin and lateral margins with 22–25 simple setae ( Fig. 4A View FIGURE 4 ).

Pleopod II protopodite subcircular, tear-shaped, with 1 robust seta near external distal angle; outer margin of exopodite proximal segment with 4 simple setae; exopodite distal article oval, margin with 17–25 long plumose setae; endopodite slender, length 3.6 times width, medial portion curved, length 1.3 times exopodite length, endopodite length 1.6 times protopodite length, internal and external process prominent, endopodite apex with 3 processes, caudal process with protuberances, cannula reaching half of caudal process with subcylindrical apex ending in acute peak, mesial process evident at base of cannula ( Fig. 3B View FIGURE 3 ); endopodite armed with 5–15 cuticular scales ( Fig. 3C, D View FIGURE 3 ).

Pleopod III exopodite oval with distal margin setose, length 1.4 times endopodite length, width 1.8 times endopodite width, with transverse suture, 23 plumose setae on distal margin, outer margin with 24–26 simple setae; endopodite small oval 1.4 times exopodite length ( Fig. 3B View FIGURE 3 ).

Pleopod IV distal margin exopodite with 10 proximal setae, length 1.6 times width; length 1.2 times endopodite length ( Fig. 4C View FIGURE 4 ).

Pleopod V exopodite subrectangular, length 1.6 times width, transverse suture present; exopodite proximal external margin with 7 simple setae, length 1.4 times endopodite length, width 1.3 times endopodite width; endopodite length 1.6 times width ( Fig. 4D View FIGURE 4 ).

Uropods length subequal to pleotelson length, armed profusely with robust setae; endopodite wide lanceolate, length 0.8 times protopodite length, length 0.7 times exopodite length; exopodite length 2.2 times width; protopodite length 1.5 times width.

Female paratype (CNCR 35082), 6.4 mm ( Fig. 1C View FIGURE 1 ); pleotelson with several setae length 2.0 eye width. Head width 2.4 times length, anterior margin concave. Eyes 2.4 times wider than long, pigmented. Post-mandibular lobes not produced, with setae as long as eye width. Pereonite 3 maximum width 2.1 mm.

Pereonites lateral margins subrectangular. Pereonite 1 length 0.85 times pereonites 2–3 length, wider than the rest. Pereonites 4–7 with lateral margins subrectangular, narrowing posteriorly with setae on lower and upper edges, length subequal to eye width.

Antennula flagellum with 9 articles, extending to base of first antennal article when projected forward; penultimate segments with aestetascs in formula 1–1–0–1. Antennas missing.

Pereopod I not as robust as in male; dactylus length subequal to palm length, internal border with distinct strong spines; palm margin with 2 rows robust setae on both lateral edges, without mesial and distal processes. Pereopod II longer than pereopod I; dactylus length subequal to propodus length. Pereopods III–VII with sub-parallel lateral margins. Pereopod VII 2.0 times body length.

Pleotelson width subequal to length, lateral margins sub-parallel, with simple setae; caudomedial lobe round- ed.

Uropods biramous, length 2.2 times pleotelson length, with simple setae; endopodite longer than protopodite, length 0.7 times protopodite length, length 0.5 times exopodite length; exopodite length 3.0 times width; protopodite length 1.6 times width ( Fig. 1D View FIGURE 1 ).

Habitat. This species was found in small reservoir, which was created by impounding a natural spring. The specimens were associated with the roots of submerged riparian vegetation, including reeds, as well as in the surface and cavities of submerged volcanic rocks within channels that flow out of the reservoir.

Distribution. Only known from the type locality.

Etymology. This species is named after Camaxtli, the god of war, faith and hunting, who is part of the Tlaxcala Valley’s mythology.

Remarks. Among the Mexican epigean species of Caecidotea   , males of C. camaxtli   sp. nov. have the longest body (13 mm in average; C. puebla   : 10.3 mm C. xochimilca   : 10.5 mm, C. williamsi   : 4.4 mm) ( Cole & Minckley 1968; Rocha-Ramírez & Peñaloza-Daniel 2011; Escobar-Briones & Alcocer 2002). C. camaxtli   sp. nov. can be distinguished from its Mexican epigean congeners by the form of the pereopods, the chaetotaxy of pereopod I, as well as the sinuous edge of the palm, having pleotelson with parallel lateral margins, rounded caudomedial lobe, and by the rounded proximal margin and tear-shape of the protopodite of pleopod II. Additionally, three processes are present on the apex of the endopodite: a long and rounded caudal process with cuticular scales, a mesial process and a short simple cannula. Caecidotea camaxtli   sp. nov. can be separated from C. communis   by the possession of a tearshape protopodite of pleopod II and by lanceolate and wider uropods which are profusely covered by setae, while C. communis   shows a subsquare protopodite of pleopod II, and narrower uropods with scarce setae covering.

Pérez-Rodríguez (1994) reported that Laguna El Ojito was slightly alkaline and morning surface temperature ranged from 14–22°C from January to October. We noted that the sedimentary environments of the lake comprised two main types: 1) lentic waters with clay bottoms, where specimens were found in association with the roots of reeds and 2) lotic waters with terrigenous, sandy or silty clay, where submerged igneous rocks provided hiding places for isopods. Individuals of C. camaxtli   sp. nov. were abundant in the habitats described above. Other common crustaceans collected concomitantly in Laguna El Ojito included the crayfish C ambarellus m ontezumae (Saussure, 1857) and amphipod Hyallela   sp. Laguna El Ojito currently represents the only known population of C. camaxtli   sp. nov. and there is uncertainty whether this species is more widely distributed or endemic to this system, which is subject to anthropogenic pressures related to water supply to nearby communities (Pérez-Rodríguez 1994).

The discovery of this new species is evidence that freshwater isopod diversity in central Mexico is likely higher than currently recorded. Fleming (1973) and Argano (1977) concluded that C. communis   (type locality: Pennsylvania, USA) was the only epigean species inhabiting Mexico. However, the description of the new species presented here and C. puebla   , C. williamsi   , and C. xochimilca   suggest that rather than one species widely ranging from Canada to Mexico, Caecidotea   species in the latter represent a mosaic of endemic/highly localized species ( Fig. 6 View FIGURE 6 ), and that C. communis   sensu stricto may be not be present in Mexico. Nine species of Caecidotea   have been recorded from Mexico, five of which are found in surface waters along the Trans-Mexican Volcanic Belt, while the rest inhabits the southwest region, specifically within the karstic basin of Chiapas in caves with subterranean aquatic habitats ( Bowman 1975, Argano 1977). We would expect an increase in the number of species with a greater sampling effort, and analysis of more populations from Mexico can be carried on.