Caecidotea contrerasbalderasi, García-Vázquez & Campos & Rodríguez-Almaráz, 2023

García-Vázquez, Leonardo, Campos, Ernesto & Rodríguez-Almaráz, Gabino A., 2023, A new and rare epigean asellid from western Mexico Caecidotea contrerasbalderasi sp. nov. (Isopoda: Asellidae) with a new suture pattern in pleopod IV for the Mexican epigean species, Nauplius 31, pp. 1-10 : 3-7

Caecidotea contrerasbalderasi sp. nov.

( Figs. 2–4 )

Zoobank: urn:lsid:zoobank.org:act:29BCA5AD-04FC-4C8F-B237-751C36E02573

Material examined. Holotype: 1 male (UANL- FCB-C-6240), length 7 mm, in freshwater pond, clear water and bottom of mud and gravel; Pantanal , municipality Xalisco, Nayarit, Mexico, 21°25’38.29”N 104°51’29.67” W, elev. 927 m, 15 February1988, coll. Gabino A. Rodríguez-Almaraz. Paratypes: 4 females and one male (UANL-FCB-C-6241) ; one specimen, unsexed ( USNM 1014039 ) .

Diagnosis. Male body length 7.0 mm, width 1.6 mm. Head trapezoidal, anterior margin concave, postmandibular lobes protruding. Pereionites I– II with concave margin. Pleotelson subquadrate, lower caudomedial lobe bilobed. Pleopod I length 1.4 × width; distal article length 1.4 × protopod length, distal article length 1.9 × width, external margin proximally concave with 4 small setae as long as retinacula. Pleopod III transverse suture with 7 presutural simple setae. Pleopod IV protopod with fringe of small setae plus 2 long simple setae. Pleopod V with 2 sinuous sutures. Uropod half as long as pleotelson.

Description. Male (UANL-FCB-C-6240) 7 mm ( Figs. 2A – 4 ). Body length 4.2 width; surface covered by scattered setae; head width 1.5 × length, anterior margin concave; without eyes; postmandibular lobes poorly developed. Pereionites subrectangular, lateral margins rounded with setae, pereionites I–II similar in length with frontal margin medially concave, pereionite I symmetrical, pereionite II with anterolateral margin front projecting, pereionites III–IV with frontal margin straight, pereionites V–VII with frontal margin convex, posterolaterally back projecting ( Fig. 2A ).

Antennula not overreaching protopodal article 3 of antenna; flagellum with 7 articles, aesthetascs in formula 1-1-1-1; articles tapering distally, first article 1.5 and 2.6 times longer than second and third segments; 1–3 longer than f lagellum. First article 1.5 and 2.6 times longer than second and third articles.

Antenna, flagellum broken in all specimens except a paratype female in which it reaches posterior margin of pleotelson, with 4 protopodal articles, and flagellum of 19 articles.

Pereiopod I ( Fig.2A ),subchelate, propodus length 1.4 × width, shorter than pereiopod II; palm outer margin convex, proximally with 2 articulated strong setae; mesial process unicuspidate, large, triangular with pointed apex not surpassing dactylus width; distal process absent; proximal process with 2 strong setae, one as long as medial process; dactylus flexor margin with 9 setae increasing in size distally, outer margin with 5 simple setae, 1 distally plumose seta; dactylus as long as inner margin of propodus. Pereiopod II (not figured) longer not as robust as pereiopod I; not subchelate; dactylus as long as propodus length. Pereiopod III ( Fig.3C ) propodus with 6 strong setae as long as dactylus unguis. Pereiopod IV( Fig.3D ) slightly longer than pereiopod II; dactylus with 2 setae on inner margin with 1 terminal setae, outer margin with 4 setae;propodus length 3.0 dactylus length, propodus length 4.0 width, outer and inner margin bearing scattered setae; with single subtriangular projection on distal margin; carpus subtrapezoidal length 2.4 × width; outer margin with 1 setae centrally placed plus 3 on posterodistal margin, inner margin with 7 spines; merus triangular, subequal as wide as long, with long, robust setae of different sizes at anterodistal angle; ischium rectangular, length 1.4 × width and about 1.1 ×merus length; basis subrectangular length 1.7 × ischium length; inner margin with 2 proximal spines plus one distal spine, outer margin with 10 spines. Pereiopod V (not figured) similar in length to pereiopod VI. Pereiopod VI ( Fig. 3H ) similar to pereiopod IV;dactylus about third as long as propodus. Pereiopod VII (not figured) 1.1 pereiopod VI length.

Pleopod I ( Fig. 4A ), longer than pleopod II; basal protopod with 4 retinacula, length 1.4 × width; distal article length 1.4 × protopod length, distal article length 1.9 × width, bearing rounded apex, mesial margin proximally concave with 4 small setae; inner margin without setae; apex with 7 simple longer setae, distally with 3 additional simple and smaller setae.

Pleopod II ( Fig. 4B ), protopod subquadrate, width 0.8 × length, with 1 medial seta; exopod proximal segment with 3lateral setae, distal segment oval, length 1.3 × width, with 11 lateral and distal setae, with numerous minute simple setae on inner distal margin; endopod narrow, length 4.0 × width, with rounded prominent lateral basal inner and outer apophyses, tip produced into terminal process, tapering and slightly curving latero-distally, cannula long simple; caudal process simple, rounded, armed with 7 cuticular scales, ventral groove simple length 4.3 × width; mesial process simple, acute; lateral process not evident ( Fig. 4C,D ).

Pleopod III ( Fig.4E ),protopod small; exopod ovate forming large operculum for remaining pleopods; distal article length 1.3 proximal article length, transverse suture with 7 presutural simple setae, external margin with 4 small simple setae, distal margins with 9 postsutural simple setae, apex with 10 plumose setae.

Pleopod IV ( Fig.4F ), protopod small bearing a basal fringe of small setae plus 2 long simple setae; exopod type B after Lewis and Bowman (1981), ovate, with single transverse suture on median margin; protopod distal article length 1.2 × proximal article length.

Pleopod V ( Fig.4G ), with 2 sinuous sutures arising near to distal third length; external margin with 3 setae; exopod ovate, length 1.9 × width.

Pleotelson, subquadrate, as long as wide, lateral margins parallel with several setae, caudomedial lobe wide protruding; lower caudomedial lobe emarginate, with 1 simple setae on each lobe; apex rounded.

Uropods half as long as pleotelson length;endopod length 1.6 × protopod length, endopod length 1.2 × exopod length.

Female paratype (UANL-FCB-C-6241) 6 mm ( Fig. 2B ) (only features differing from male are illustrated and described, Fig. 3 ).

Pereiopod I ( Fig. 3B ) slender; propodus length 2.5 × width; palm without process and with unequal simple setae; dactylus with 5 setae on flexor margin. Pereiopod II ( Fig. 3E ) longer than pereiopod I; not subchelate; dactylus length 3.3 × propodus length, with 1 seta on inner margin plus 1 terminal setae; propodus length 6.0 × width; inner and outer margin with 7 simple setae bearing scattered smaller ones, inner margin with 5 simple setae bearing distally a sclerotized triangular process. Pereiopod IV ( Fig. 3F ) slightly longer than pereiopod II; dactylus with 1 seta on inner margin and a larger terminal setae, outer margin with 3 simple setae; propodus length 2.4 × dactylus length, outer margin with 6 large setae with smaller setae intercalated, inner margin with 4 setae with single subtriangular projection on their distal margin; carpus subtrapezoidal length 3.0 × width; outer margin with 2 setae centrally placed, 2 on posterodistal margin, inner margin with 4 setae; merus triangular, length 1.3 × width, with 2 strong setae at anterodistal angle; ischium rectangular, length 2.2 width, 1.2 times as long as merus;basis subrectangular length 1.4 × ischium length, 2.3 times as long as wide; inner margin without setae, outer margin with 3 simple setae plus 1 plumose seta. Pereiopod VI ( Fig. 3G ) longer and more robust than pereiopod II and IV; dactylus with 1 spine on inner marginal plus a greatest terminal spine; outer margin with 1 simple seta plus 1 short seta; propodus length 6.0 × width.

Etymology. The present species is named in honor of Dr. Salvador Contreras-Balderas, as a posthumous tribute to his important and successful career as a taxonomist of fishes and crustaceans, as well as Professor of Systematics and Evolution in the Facultad de Ciencias Biológicas of the Universidad Autónoma de Nuevo León.

Habitat. The species was collected in a crystalline, freshwater shallow pond at 20 cm deep (temperature 24–26 oC) under submerged rocks and between the decaying organic matter (willow leaves), with muddy and gravelly bottom.

Distribution. Only known from the type locality.

Remarks. Morphologically, the eyes in the type series of Caecidotea contrerasbalderasi sp. nov. are absent, as well as body pigmentation, features usually associated with a subterranean lifestyle ( Rudy et al., 2018). In contrast, this species does not present elongation of appendages such as pereiopods, antennae or uropods. A similar situation is found in some Eastern Australian phreatoicidean isopods belonging to the genus Crenoicus and in the New Zealand genus Notamphisopus , in which epigean species lack functional eyes and pigmentation ( Fenwick et al., 2009; Wilson and Ho, 1996).

Figures

Figure 2. Caecidotea contrerasbalderasi sp. nov., Pantanal, municipality Xalisco, Nayarit, Mexico. A, Holotype male (UANL- FCB-C-6240), 7.0 mm.B, Paratypefemale (UANL-FCB-C-6241) 6.0 mm.A, male habitus.B, female habitus.Scale bars = 1.0 mm.

Figure 3. Caecidotea contrerasbalderasi sp.nov., holotypemale (UANL-FCB-C-6240), 7.0 mm, paratypefemale (FCB-UANL-6241), Pantanal, municipalityXalisco,Nayarit, Mexico.A, male pereiopodI; B, female pereiopodI; C, malepereiopod II; D, male pereiopod III; E, female pereiopod IV; F, pereiopod V; G, female pereiopod VI. H, pereiopod VII. Scale bar: A, B = 0.15, C-H = 0.2 mm.

Figure 4. Caecidotea contrerasbalderasisp.nov.,holotype male(UANL-FCB-C-6240),7.0 mm, left pleopods,Pantanal, Municipality Xalisco, Nayarit, Mexico. A, pleopod I; B, pleopod II; C, D, dorsal and ventral view of the apex of the endopodite; E, pleopod III; F, pleopod IV; G, pleopod V. Scale bars: A, B = 0.1 mm, C, D = 0.054 mm, E-G = 0.2 mm.