Hyalella alvarezi sp. nov.

http://www.zoobank.org/ urn:lsid:zoobank.org:act: 14E267AE-A7D5-4E38-A00A -1CA79136C1FF

(Figures 5–7)

Etymology. The new species is named in honour of Dr Fernando Alvarez Noguera for his important contribution to carcinological study in Mexico.

Material examined. Holotype male, size 4.4 mm (Cat. No. CNCR 35727), from Lake La Encantada in state of Veracruz, Mexico (18.458°N, 95.185°W), 24 July 2015, 332 m a.s.l., temp. 30°C, pH 7. Collectors: A. Marrón-Becerra, E. Lemus-Santana and M. HermosoSalazar. Paratypes (n = 30 males, n = 30 females): males – mean size 4.4 ± 0.5 mm, mean head length 0.6 ± 0.03 mm (n = 27), females – mean size 4.5 ± 0.5 mm, mean head length 0.5 ± 0.04 (n = 25) (permanent slides Cat. No. CNCR 35735, paratypes and SEM preparations CNCR 35736), locality same as holotype .

Type locality (Figure 1c). Lake La Encantada, state of Veracruz, Mexico (18.458°N, 95.185°W).

Diagnosis. Pleonite 1 and 2 with dorsoposterior carina. Coxa 4 excavated posteriorly. Eyes pigmented. Antenna 1 shorter than antenna 2. Antenna 2 less than half body length. Maxilla 1 palp short, overreaching half of length between base of palp and base of setae in outer plate, with 1 stout distal seta; base of the seta covered by a cylindrical structure, setules present; inner plate slender with 3 strong pappose distal setae. Maxilla 2 inner plate with 2 strong pappose setae on inner margin. Gnathopod 1, propodus hammer shaped, palm slope transverse, inner face with 4 serrate setae, comb scales on distoposterior and distoanterior border, carpus inner lobe with 3–4 serrate setae. Gnathopod 2, basis hind margin with 2 setae and denticles in polygonal pattern. Uropods without curved setae. Uropod 3, peduncle and ramus subequal in length, styliform. Telson as long as wide, distal margin truncated, with 2 long simple apposed setae. Coxal gills on segments 2–6. Sternal gills on segments 3–7.

Description of male

Body (Figures 5a, and 17c), tergites of pleon 1 and 2 with dorsoposterior carina. Epimeral plates 1–3 slightly acuminate. Coxae 1–3 (Figures 5a, and 17c) subequal in shape, subrectangular, longer than wide, coxa 4 wider than coxae 1–3 with deep posterior excavation, acumination absent. Coxa 5 with two subequal lobes. Coxa 6 anterior lobe reduced, coxa 7 anterior lobe absent.

Head typically gammaridean (Figures 5a, and 17c), smaller than first two thoracic segments, rostrum absent. Eyes pigmented, medium, rounded, located between insertions of antennae 1 and 2.

Antenna 1 (Figure 5a–b) less than half body length, shorter than antenna 2 (80% length of antenna 2), but longer than peduncle of antenna 2, almost reaching to middle of third pereonite; peduncle longer than head, reaching to middle of length of first pereonite; article 1 and 2 subequal in length, article 1 wider than articles 2–3, article 2 longer and wider than article 3, proportions (1.3:1.26:1), article 1 with 3 short setae ventrally, 1 smaller, and one cluster with 3 cuspidate setae at distal end, articles 1–3 mid-ventral margin with slender setae; flagellum longer than peduncle with 9 articles becoming gradually shorter towards distal portion; aesthetascs on flagellum, present on articles 2–6 (one pair), 7–8 (one).

Antenna 2 (Figure 5a, c) almost 1.27 times longer than antenna 1, reaching one-third body length, reaching fourth pereonite; peduncle reaching second pereonite, peduncle articles increase gradually in length and decrease in width; article 3 shorter but wider than 4 and 5, article 4 longer than article 3, article 5 slightly longer than article 4 (almost 1.3 times); flagellum with 8–10 articles, slightly longer than peduncle, without aesthetascs.

Buccal parts: upper lip (Figure 5f), distal margin rounded with numerous setules.

Lower lip (Figure 5g) subquadrate, outer lobes without notches or excavations, mandibular projection of outer lobes rounded.

Mandibles (Figure 5h–i), without palp, asymmetric; incisor toothed, 6 teeth present. Left lacinia mobilis with 5 teeth; setal row on left mandible with 3 main pappose setae plus accessory setae. Right mandible with 5 teeth, right lacinia mobilis reduced, with 2 pairs of asymmetric L-shape teeth; setal row on right mandible with 2 main pappose setae plus accessory setae and with setulae near molar process. Molar process large, cylindrical and triturative, with accessory pappose seta in both molars.

Maxilla 1 (Figures 5d, and 19c), palp short, uniarticulate, longer than wide, distally pointed with 1 short distal stout distal seta (A 5 type), with a cylindrical structure near the base that covers almost one-third of distal seta, setules present; palp length slightly exceeds one-half of distance between base of palp and base of seta on outer plate (Figures 5d, and 19c); inner plate slender, shorter than outer plate, with 3 pappose distal setae; outer plate with 9 distal stout serrate setae and with setules.

Maxilla 2 (Figure 5e) plates subequal; inner plate shorter and slender with 2 pappose setae on mid-distal inner margin, distal margin with abundant setae and 6 serrulate setae; outer plate without serrate setae but with 2 long pappose setae; outer and inner plates with large simple distal setae (type A2) and abundant setules on both distal surfaces and margins.

Maxilliped (Figures 5j, and 20c) inner plate lobe longer than outer plate lobe, distal margin slightly convex, in both plates, inner plate distal margin with 3 cuspidate setae of equal size and with plumose setae, inner margin with several pappose setae; outer plate, inner and distal margins with numerous simple setae. Palp composed of four articles subequal in maximum length, first article with 3 simple setae at inner distal end and without seta on outer distal end; second article with numerous simple setae on inner margin and 3 on the outer distal end; third article with several setae on distal margin, distal end of outer margin with 4 simple setae and comb scales, inner margin with at least 8 setae and at least 5 at distal end; fourth article unguiform slightly longer than nail, with comb scales, inner margin near distal half with 2 setae, and 1 seta near nail base on outer margin; nail exceeds 2/3 of fourth article, with serration at distal half.

Gnathopod 1 (Figure 6a) subchelate, hammer shaped. Basis elongated, maximum length almost 3 times longer than maximum width; posterior margin with 1 seta, distal end with one cluster of 2 setae. Ischium short, subquadrate, slightly longer than wide, length almost same as maximum width of basis and maximum length of merus, distal posterior end with one cluster of 4 setae. Merus longer than wide, ventral surface with comb scales, distal margin with 7 setae. Carpus longer than wide, longer than propodus; with strong, short, and wide posterior lobe and forming one scoop-like structure, open to inside; lobe, inner surface with 2–3 serrate setae. Propodus 1.5 times longer than wide, inner surface near distal margin with 3–4 serrate setae (3 in a row), outer surface near half of margin with 1 seta; distal anterior end with two clusters of approximately 8 setae; distal anterior and posterior surfaces with comb scales; palm transverse, posterior distal end with 1 robust seta and cup for dactylus. Dactylus claw-like; nail present; with 1 plumose seta, and comb scales.

Gnathopod 2 (Figures 6b, and 21c) subchelate; palm slightly oblique. Basis elongate, more than 3 times longer than wide; posterior margin with 1–2 long setae and denticles in polygonal pattern. Ischium short, subquadrate, shorter than merus. Merus short; posterior margin with 1 seta and distal end of posterior margin with 5 simple setae; posterior inner and outer surfaces with comb scales. Carpus shorter than propodus; anterodistal end with 5 setae; posterior lobe scoop-like, elongate, almost 1.5 times width of merus, with several submarginal pappose setae and comb scales. Propodus robust, almost 1.3 times as long as wide, subrectangular, palm slightly shorter than posterior margin; slope slightly irregular, with several long simple setae, and some short and medium setae; distal margin of palm with one truncated process near insertion of dactylus and with narrow posterior excavation at base (Figure 22c); palm posterior distal end with 2 strong setae, comb scales, and cup for the dactylus. Dactylus claw-like, congruent with palm, without comb scales; outer margin with 1 plumose seta; inner margin with setules widely separated, crenulation absent.

Pereopods 3–7 (Figure 6e–i) simple, gradually longer posteriorly; pereopod 5 shorter than 4 and 6.

Pereopod 3 (Figure 6e), basis elongate; mid-posterior margin with 1 simple seta. Merus anterior margin with 1 long simple seta; posterior margin with 3 setae; anterodistal and posterodistal end with one cluster of 4 setae. Carpus slightly shorter and slenderer than merus; posterior margin with 4 stout setae plus accessory seta; anterodistal end with at least 5 slender setae, posterodistal end with at least 2 setae. Propodus slenderer than carpus; posterior margin with 4 setae; anterodistal end with 6 simple setae. Dactylus clawlike, length less than half of propodus; nail present.

Pereopod 4 (Figure 6f) similar in shape to pereopod 3 but slightly longer, coxa 4 wider than coxa 3 with posterior excavation; basis posterior margin with 1 simple seta; merus mid anterior margin with 1 stout setae; propodus posterior margin with 3–5 setae.

Pereopods 5–7 (Figure 6g –i) similar in shape, basis posterior lobe rounded and denticulated; pereopod 7 (Figure 6i) basis lobe widely expanded, almost reaching ischium distal margin; wider than lobes in pereopods 5 and 6; basis lobe width as wide as 1.5 times the basis (measured at cleft between basis and basis lobe); posterior margin with 10–12 serrations, each with 1 setule but 2–4 serrations with 1 stout seta on distal margin; anterior margin with three clusters of 2 stout setae and one cluster of 2 setae at distal end. Dactylus length less than half of propodus length.

Pleopods 1–3 (Figure 7e) not modified, biramous, elongated, rami multi-annulated, with numerous plumose setae; pleopod 1, inner margin of peduncle at distal end with 2 short retinacula (coupling hooks).

Uropod 1 (Figure 7a) longer than uropod 2 (Figure 7b); peduncle longer than rami, dorsal margin with 2 setae; inner and outer distal ends each with 1 seta; rami subequal, inner ramus slightly longer, with 2 dorsal and 4 distal setae, outer ramus with 2 dorsal and 4 distal setae; male without curved setae on inner ramus.

Uropod 2 (Figure 7b) as long as peduncle of uropod 1; peduncle slightly longer than outer rami, with 1 dorsal seta, inner and outer distal ends each with 1 seta; rami subequal; inner ramus slightly longer with 2 dorsal and 3 distal setae; outer ramus with 2 dorsal and 4 distal setae.

Uropod 3 (Figures 7c, and 23c) peduncle rectangular, wider than ramus, with 5 strong distal setae of variable length; inner ramus absent; outer ramus uniarticulate, slender, slightly shorter than peduncle, with 4 slender apical setae and 1 connate seta.

Telson (Figures 7d, and 24c) entire, as long as wide, distal margin pointed, with 2 long simple setae apposed; two clusters of 3 plumose setae symmetrically distributed.

Coxal gills sac-like, present on segments 2–6 (Figure 6h, dotted line). Sternal gills tubular, present on segments 3–7 (Figure 6h, dotted line).

Female (Figure 17d) similar to male. Gnathopod 1 (Figure 6c), carpus with 3 serrate setae on the inner face lobe. Propodus with 4 serrate setae in a row over the inner face, and 3 long setae on a row on the outer face. Gnathopod 2 (Figure 6d) smaller than male gnathopod 2, parachelated, palm reverse oblique, basis posterior margin with 1 seta; propodus longer than twice maximum width, outer face with 3–4 serrate setae in a row and 1 large seta near the palm, anterior and posterior distal half with comb scales. Pereonite 2 with one anterior excavation or notch for amplexus. Pereopod 7 lobes with 9 serrations and setules, and with 2 stout setae on the distal margin. Oostegites subtriangular, almost reaching one-half length of merus, with setae curled on the margins.

Intraspecific variation. The palp of maxilla 1 is short and varies in length and form in the same organism or if is moulting; can reach a maximum length of almost 2 times width and presents constricted margin in the middle.

Habitat. Freshwater, epigean, littoral, associated with Eichhornia crassipes (Mart.) Solms.

Distribution. Lake La Encantada, state of Veracruz, Mexico (18.458°N, 95.185°W).

Remarks

Hyalella alvarezi sp. nov. (La Encantada, Veracruz) shares morphological traits with the other species from Veracruz and with H. wakulla from Florida, such as the dorsal mucronations (except in H. garyi sp. nov.), and the telson with 2 distal setae apposed, similar to H. azteca s.s. (except in H. sarukhani sp. nov., and H. garyi sp. nov.). This species can be distinguished primarily by the presence of one cylindrical base covering almost one-third of the distal setae in palp of maxilla 1, the polygonal pattern (denticles) over the surface of basis in male gnathopod 2 (similar to H. gauchensis Streck and Castiglioni, 2017, H. georginae Streck and Castiglioni, 2017 and H. rioantensis Penoni and Bueno, 2020 – i.e. the three from southern Brazil), and one slender excavation in the palm of male gnathopod 2. On the other hand, this species shares morphological characters with H. sarukhani sp. nov. (Tables 1, S1–S 2).