Hyalella sarukhani Marrón-Becerra & Hermoso-Salazar 2022, sp. nov.

Hyalella sarukhani sp. nov.

http://www.zoobank.org/ urn:lsid:zoobank.org:act: 7B0E06D1-9F55-4345-9055- 9054F8B9B450

(Figures 2–4)

Etymology. The new species is named in honour of Dr José Sarukhán in recognition of his outstanding contribution to the study of the biodiversity of Mexico.

Material examined. Holotype male, size 7.7 mm (Cat. No. CNCR 35726), from Lake Chapultepec (19.424°N, 99.187°W), 10 August 2016, 2253 m a.s.l. collector: A. Marrón-Becerra. Paratypes (n = 10 males, n = 10 females): males – mean size 6.4 ± 0.5 mm, mean head length: 0.6 ± 0.03 mm (n = 10), females – mean size 6.2 ± 0.4 mm, mean head length 0.5 ± 0.04 (n = 10) (permanent slides Cat. No. CNCR 35731, paratypes and SEM preparations Cat. No. CNCR 35732), locality same as holotype. Other material revised Xochimilco (19.264°N, 99.094°W), 10 August 2016, 2240 m a.s.l., collector A. Marrón-Becerra (Cat. No. CNCR 35733). Lake Chalco, Mexico City (19.264°N, 98.974°W), 29 March 2016, 2231 m a.s.l., temp. 24°C, pH 8.7, conductivity 1793 µS/cm, dissolved oxygen 2.8 mg /L, collectors: A. Marrón-Becerra and F. Charqueño-Celis (Cat. No. CNCR 35734).

Type locality (Figure 1a). Lake Chapultepec, Mexico City, Mexico (19.424°N, 99.187°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, reaching less than half of length between base of palp and tip of setae in outer plate, with 1 short stout distal seta and setules; inner plate slender with 2– 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 5–6 serrate setae, comb scales on distoposterior and distoanterior border, carpus inner face lobe with 5 serrate setae. Gnathopod 2, basis hind margin with 3–5 setae, merus with 1 medial seta, excavation of palm wide. Uropods without curved setae. Uropod 3, peduncle and ramus subequal in length, styliform. Telson slightly wider than long, distal margin rounded with 2 long simple setae widely separated. Coxal gills on segments 2–6. Sternal gills on segments 3–7.

Description of male

Body (Figures 2a, and 17a), tergites of pleon 1 and 2 with dorsoposterior carina. Epimeral plates 1–3 acuminate. Coxae 1–3 (Figures 2a, and 17a) 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, anterior lobe slightly shorter than posterior, coxa 6 anterior lobe reduced.

Head typically gammaridean (Figures 2a, and 17a), shorter than first two thoracic segments, reaching to middle of second pereonite, rostrum absent. Eyes pigmented, black, medium, rounded, located between insertions of antennae 1 and 2.

Antenna 1 (Figure 2a–b) less than half the body length, shorter than antenna 2, but longer than peduncle of antenna 2, almost reaching to middle of third pereonite; peduncle as long as head; article 1 and 2 subequal in length, article 1 wider than articles 2–3, article 2 longer and wider than article 3, (proportions 1.8:1.6:1), article 1 with 2 short cuspidate setae ventrally, 1 smaller, and one cluster with 3 cuspidate setae at distal end; flagellum longer than peduncle with 9–10 articles gradually shorter towards distal portion; aesthetascs present on articles 4–7 (one pair), and 8–9 (one aesthetasc).

Antenna 2 (Figure 2a, c) almost 1.3 times longer than antenna 1, slightly shorter than one-third body length, reaching fourth pereonite; peduncle almost reaching to middle of first 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 (almost 1.5 times); flagellum with 11–12 articles, longer than peduncle (almost 1.5 times); without aesthetascs.

Buccal parts: upper lip (Figure 2f) distal margin rounded, with numerous setules.

Lower lip (Figure 2g), subquadrate, outer lobes without notches or excavations; mandibular projection of outer lobes rounded.

Mandibles (Figure 2h–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-shaped 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 (Figures 2d, and 19b), palp short, uniarticulate, longer than wide, distally pointed with 1 short and stout distal seta, setules present; palp length almost half of distance between base of palp and base of seta on outer plate, but less than half distance between base of palp and tip of seta on outer plate (Figures 2d, and 19b); inner plate slender, shorter than outer plate, with 2–3 pappose distal setae; outer plate with 9 stout serrate setae and with setules.

Maxilla 2 (Figure 2e) plates subequal; inner plate shorter and slender, with 2 pappose setae on mid-distal margin, and with 7 shorter serrulate setae on distal margin; outer and inner plates with large simple distal setae (type A2) and abundant setules on both distal surfaces and margins.

Maxilliped (Figures 2j, and 20b) inner plate lobe longer than outer plate lobe; distal margin slightly convex, on 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 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, distal end of outer margin with 3 simple setae and comb scales, inner margin with at least 12 setae and 6 at distal end; fourth article unguiform, longer than nail, with comb scales; nail almost reaching 2/3 of fourth article, with serration at distal half.

Gnathopod 1 (Figure 3a) 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 2 setae. Ischium short, subquadrate, distal posterior end with 2 clusters of 2 setae. Merus longer than wide, almost distal half of length of ventral surface with comb scales; distal margin with 5–6 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; inner surface with 5–6 serrate setae, Propodus 1.5 times longer than wide; inner surface near distal margin with 5–6 serrate setae in one row; distal anterior end with two clusters of approximately 5 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 3b, and 21b) subchelate; palm slightly oblique. Basis elongate, more than 3 times longer than wide; posterior margin with 3–5 long setae. Ischium short, subquadrate, shorter than merus. Merus short; posterior margin with 1 seta and distal end of posterior margin with 8 simple setae; posterior inner and outer surfaces with comb scales. Carpus shorter than propodus; anterodistal end with 3 setae; posterior lobe scooplike, elongate, with several submarginal pappose setae and comb scales. Propodus robust, length slightly less than 1.5 times maximum wide, subrectangular; palm slightly shorter than posterior margin; slope slightly irregular, with several long simple setae, and few short and medium setae; distal margin of palm with one truncated process near insertion of dactylus and with one wide posterior excavation at base (Figure 22b); palm posterior distal end with 2 strong setae, comb scales and cup for dactylus. Dactylus claw-like, congruent with palm, without comb scales; outer margin with 1 plumose seta; inner margin crenulate with separated setules.

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

Pereopod 3 (Figure 3e), basis elongate; mid-posterior margin with 1–2 simple setae. Merus longer than ischium (almost 3 times the maximum length); anterior margin with 2 setae; posterior margin with 6 setae; anterodistal and posterodistal ends each with one cluster of 4–5 setae, lobe less than one-fourth length of carpus. Carpus shorter and slenderer than merus; posterior margin with 5 stout setae plus accessory setae; posterodistal end with at least 5 slender setae; anterodistal end with at least 2 setae. Propodus shorter than anterior margin of merus, slenderer than carpus; posterior margin with 7 stout setae; anterodistal end with 5 simple setae. Dactylus claw-like, length slightly overreaching half of propodus; nail present.

Pereopod 4 (Figure 3f) similar in shape to pereopod 3 but slightly longer; coxa 4 wider than coxa 3 with posterior excavation; basis posterior margin with 1–2 simple setae; merus mid-anterior margin without setae; propodus posterior margin with 6 setae.

Pereopods 5–7 (Figure 3g –i) similar in shape; basis posterior lobe rounded and denticulated. Pereopod 7 (Figure 3i) 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 wide as basis (measured at cleft between basis and basis lobe); posterior margin with 19 serrations, each with 1 setule (17) but 2 serrations with 1 stout seta on distal margin; anterior margin with two clusters of 2 stout setae on distal half and 1 at distal end. Dactylus length almost half of propodus length.

Pleopods 1–3 (Figure 4e) 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 4a) longer than uropod 2 (Figure 4b); peduncle longer than rami, with 3 dorsal setae, inner and outer distal ends each with 1 seta; rami subequal, inner ramus slightly shorter, with 2 dorsal and 4 distal setae, outer ramus with 3 dorsal and 4 distal setae; male without curved setae on inner ramus.

Uropod 2 (Figure 4b) longer than peduncle of uropod 1; peduncle as long as rami, with 2 dorsal setae and 2 additional distal setae; rami subequal, inner ramus slightly longer, with 2–3 dorsal and 4 distal setae, outer ramus with 3 dorsal and 5 distal setae.

Uropod 3 (Figures 4c, and 23b) slightly shorter than peduncle of uropod 2; peduncle rectangular, wider than ramus with 5 strong distal setae of variable length; inner ramus absent; outer ramus uniarticulate, slender, slightly shorter than peduncle, 2 times the length of larger seta of peduncle, basal width near 2 times width of apex of ramus, with 3 slender apical setae and 1 connate seta.

Telson (Figures 4d, and 24b) entire, as long as wide, distal margin rounded with 2 long simple setae widely separated by almost one-third of maximum width of telson; and two lateral clusters of 3 plumose setae symmetrically distributed.

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

Female (Figure 17b) similar to male. Gnathopod 1 (Figure 3c), ischium distal half of posterior surface with comb scales; carpus with 3 serrate setae on inner face lobe; propodus with 4–5 serrate setae in row over the inner face. Gnathopod 2 (Figure 3d) smaller than male gnathopod 2, parachelated, palm reverse oblique; basis posterior margin with 2–3 setae; ischium distal half of posterior surface with comb scales;propodus slightly longer than twice maximum width, outer face with 3 serrate setae in one row and 3 large setae near palm, anterior and posterior distal half with comb scales. Pereonite 2 with one anterior excavation or notch for amplexus. Pereopod 7 lobe with 13 serrations and setules, and 2 stout setae on distal margin. Oostegites subtriangular with curled setae on margins.

Intraspecific variation. Gnathopod 2 of male, basis hind margin up to 5 setae (some organisms from Chalco). Pereopod 3 merus posterior margin up to 4 setae (organisms from Chalco).

Habitat. freshwater, epigean, littoral, found associated with roots of Lemna sp.

Distribution. Mexico City, Mexico.

Remarks

Hyalella sarukhani sp. nov. (from Mexico City) can be easily distinguished from species in the Hyalella azteca complex by the telson with rounded distal margin and the presence of 2 long setae wide apart (almost one-third of maximum width of telson). This species has more serrations in the posterior margin of the lobe of pereopod 7 but less stout setae on the distal margin than H. azteca. This species bears setules on the palp of maxilla 1, in contrast with Hyalella wakulla (Drumm and Knight, 2019). The morphological differences from the other Hyalella species described in this work are summarised in Tables S1 and S2 (Table 1).