Hyalella viviannae sp. nov.

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(Figures 8–10)

Etymology. The new species is named in honour of Dra Vivianne Solís-Weiss, in recognition of her studies of marine and estuarine invertebrates in Mexico.

Material examined. Holotype male, size 4.9 mm (Cat. No. CNCR 35728) from Lake San Julian, state of Veracruz, Mexico (19.256°N, 96.265°W), 24 July 2015, 5 m. a.s.l., temp. 37°C, pH 7.8. Collectors: A. Marrón-Becerra, E. Lemus-Santana and M. Hermoso-Salazar. Paratypes (n = 30 males, n = 30 females): males – mean size 4.5 ± 0.6 mm (n = 27), mean head length 0.6 ± 0.03 mm (n = 10), females – mean size 4.3 ± 0.4 mm, mean head length 0.6 ± 0.03 (n = 30) (permanent slides Cat. No. CNCR 35737, paratypes and SEM preparations CNCR 35738), locality same as holotype .

Type locality (Figure 1b). Lake San Julian, state of Veracruz, Mexico (19.256°N, 96.265° 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 tip of setae in outer plate, with 1 large stout distal seta and setules; 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 face lobe with 3 serrate setae. Gnathopod 2, basis hind margin with 2 serrate setae. Uropods without curved setae. Uropod 3, peduncle slightly shorter than ramus, ramus styliform. Telson slightly longer than width, distal margin rounded with 2 long simple apposed setae. Coxal gills on segments 2–6. Sternal gills on segments 3–7.

Description of male

Body (Figures 8a, and 17e), tergites of pleon 1 and 2 with dorsoposterior carina. Epimeral plates 1–3 slightly acuminate. Coxae 1–3 (Figures 8a, and 17e) subequal in shape, subrectangular, longer than wide; coxa 4 wider than coxae 1–3 with deep posterior excavation; acumination absent. coxa 5 anterior lobe slightly shorter than posterior; coxa 6 anterior lobe reduced; coxa 7 anterior lobe absent.

Head typically gammaridean (Figures 8a, and 17e), shorter than first two thoracic segments, rostrum absent. Eyes pigmented, medium, rounded, located between insertions of antennae 1 and 2.

Antenna 1 (Figure 8a–b) less than half body length, shorter than antenna 2, but longer than peduncle of antenna 2; peduncle longer than head, almost reaching second pereonite; articles 1 and 2 subequal in length, article 1 wider than articles 2–3, article 2 longer and wider than article 3 (proportions 1.6:1.3:1), article 1 almost reaching half ventral surface with 1 short cuspidate seta and with one cluster with 3 cuspidate setae at ventral-distal end, articles 2–3 without mid-ventral margin setae; flagellum longer than peduncle with 6 articles gradually shorter towards distal portion; aesthetascs present on articles 3–5 (one).

Antenna 2 (Figure 8a, c) almost 1.2 times longer than antenna 1, reaching one-third body length, almost reaching fifth pereonite; peduncle almost reaching the second pereonite, peduncle articles increase gradually in length and decrease in width; article 3 shorter but wider than 4 and 5, article 4 slightly longer than article 3, article 5 longer than article 4 (less than 1.5 times); flagellum with 7–9 articles, slightly longer than peduncle (almost 1.5 times); without aesthetascs.

Buccal parts: upper lip (Figure 8f) distal margin rounded with numerous setules.

Lower lip (Figure 8g), subquadrate, outer lobes without notches or excavations, mandibular projection of outer lobes rounded.

Mandibles (Figure 8h–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 6 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. Both molar processes large, cylindrical and triturative, with accessory pappose setae.

Maxilla 1 (Figure 8d and 19d), palp uniarticulate, longer than wide, distally pointed with 1 stout distal seta, seta length reaching one-third of palp length, setules present; palp length almost reach 2/3 of distance between base of palp and base of seta on outer plate, almost half distance between base of palp and tip of seta on outer plate (Figure 8d); inner plate slender, shorter than outer plate with 2–3 pappose distal setae; outer plate with 9 stout distal serrate setae and with setules (Figure 8d).

Maxilla 2 (Figure 8e) plates subequal; inner plate shorter and slender, with 2 pappose setae on mid-distal margin, and with 7 shorter paposerrate setae; outer and inner plates with large simple distal setae (A 2 type) and abundant setules on both distal surfaces and margins.

Maxilliped (Figures 8j, and 20d) inner plate lobe longer than outer plate lobe; distal margin slightly convex; 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 1 seta at outer distal end; second article with numerous simple setae on inner margin and 3 on outer distal end; third article with several setae on distal margin, outer margin with 4 simple setae and comb scales, inner margin with 5–6 setae and at least 9 at distal end; fourth article unguiform, longer than nail, with comb scales, inner margin near distal half with 3 setae and 1 near nail base on outer margin; nail exceeds 2/3 of fourth article, with serration at distal half.

Gnathopod 1 (Figure 9a) subchelate, hammer shaped. Basis elongated, maximum length almost 3.5 times longer than maximum width; posterior margin with 1 seta, distal end with one cluster of 4 setae. Ischium short, subquadrate; distal posterior end with two clusters of 2 setae. Merus longer than wide, ventral surface with comb scales; distal margin with 5 setae. Carpus longer than wide, longer and slightly wider than propodus, with strong, short, and wide posterior lobe, forming one scoop-like structure, open to inside; lobe inner surface with 3 serrate setae. Propodus maximum length less than 1.5 times longer than wide; inner surface near distal margin with 4 serrate setae in one row, distal anterior end with one cluster of approximately 7 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 9b, and 21d) subchelated; palm slightly oblique. Basis elongate, more than 3 times longer than wide; posterior margin with 1–2 setae. Ischium short, subquadrate, shorter than merus. Merus short, posterior margin with 8 simple setae; distal third of posterior inner and outer surfaces with comb scales. Carpus shorter than propodus; anterodistal end with 3 setae; posterior lobe scoop-like, elongate, with several submarginal pappose setae and comb scales. Propodus robust, length slightly exceeds 1.5 times as long as wide (1.6 times), subrectangular; palm slightly shorter than posterior margin; slope slightly irregular, with several long simple setae, and few and médium setae; inner face with 4 submarginal thinner simple setae; palm, distal margin, with one truncated process near insertion of dactylus, and without posterior excavation at base, angle stepped (Figure 22d); 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 proximal third with one plumose seta, inner margin crenulate with separated setae.

Pereopods 3–7 (Figure 9e–i) simple, gradually longer posteriorly. Pereopod 5 shorter than 4 and 6.

Pereopod 3 (Figure 9e), basis elongate, mid-posterior margin with 1 simple seta. Merus; anterior margin with 2 setae; posterior margin with 4 setae, anterodistal end with one cluster of 2 setae and posterodistal end with one cluster of 4–5 setae. Carpus shorter and slenderer than merus; posterior margin with 4 stout setae plus accessory setae; posterodistal end with at least 4 slender setae; anterodistal end with at least 2 setae. Propodus shorter than posterior margin of merus; posterior margin with 4 setae; anterodistal end with 5 simple setae. Dactylus claw-like, length almost half of length of propodus; nail present.

Pereopod 4 (Figure 9f) 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 seta; propodus posterior margin with 5 stout setae.

Pereopods 5–7 (Figure 9g –i) similar in shape, basis posterior lobe rounded and denticulated. Pereopod 7 (Figure 9i) basis lobe widely expanded, almost reaching ischium distal margin; wider than lobes of pereopods 5 and 6; basis lobe, width almost 1.5 times as width as basis (measured at cleft between basis and basis lobe); posterior margin with 15 serrations, each with 1 setule (13) but 2 serrations with 1 stout seta on distal margin; anterior margin, distal end with three clusters of stout setae on distal half and one cluster of 3 stout setae at distal end. Dactylus length almost half of propodus length.

Pleopods 1–3 (Figure 10e) 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 10a) longer than uropod 2; peduncle longer than rami, dorsal margin with 3 dorsal setae, 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; male without curved setae on inner ramus.

Uropod 2 (Figure 10b) slightly longer than peduncle of uropod 1; peduncle as long as outer ramus, with 1 dorsal seta and 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 10c, and 23d) length similar to peduncle of uropod 2; peduncle rectangular, wider than ramus, with 4 strong distal setae of variable length; inner ramus absent; outer ramus uniarticulate, slender, slightly longer than peduncle, more than 2 times (almost 3 times) length of larger setae of peduncle, basal width near 3 times width of apex of ramus, with 3 slender apical setae and 1 connate seta.

Telson (Figures 10d, and 24d) entire, longer than wide, narrowing posteriorly, with 2 long simple apposed setae; outer surface with two clusters of 3 plumose setae near middle distal portion, near margin, symmetrically distributed.

Coxal gills sac-like, present on segments 2–6. Sternal gills tubular, present on segments 3–7.

Female (Figure 17f) similar to male. Gnathopod 1 (Figure 9c), carpus with 2 serrate setae on inner face lobe; propodus with 3 serrate setae in a row over the inner face. Gnathopod 2 (Figure 9d) smaller than male gnathopod 2, parachelated; palm reverse oblique; basis posterior margin with 1 seta; propodus slightly longer than twice maximum width, outer face with 2 serrate setae in a row and 1 large seta near the palm; anterior and posterior distal half with comb scales. Pereonite 2 with an anterior excavation or notch for amplexus. Pereopod 7 lobes with 10 serrations and setules, and with 3 stout setae on the distal margin. Oostegites subtriangular with setae curled on the margins.

Intraspecific variation. The palp of maxilla 1 is short but presents differences in length and form; especially if the organism is moulting, it could reach almost 2 times its length and present a constricted margin in the middle.

Habitat. Freshwater, epigean, littoral, associated with roots of Typha dominguensis Pers, found in the sediment.

Distribution. Lake San Julian, state of Veracruz, Mexico (19.256°N, 96.265°W).

Remarks

Hyalella viviannae sp. nov. is similar to H. azteca and the other species from state of Veracruz; however, this species can be recognised by the relatively long distal seta in the palp of maxilla 1, the absence of one notch in the palm of gnathopod 2 in males (angle step), the relative length of the ramus in uropod 3 (longer than peduncle), and the form of the telson – longer than wide with 2 apposed setae and the distal margin rounded.)