Hyalella fatimae Verónica & Alejandra 2022, n. sp

Hyalella fatimae n. sp. (Figs. 1–7) Type locality. Argentina, Salta Province, Los Andes Department: 24°13’6.41’’S 66°28’24.09’’W (Fig. 1), 4458 m a.s.l., peatbog near to Chorrillos. Type specimens: Holotype male, body length 8.10 mm (FML-CRUST 01273). Paratypes: one female (ovigerous), body length 6.92 mm (FML-CRUST 01274); two males, body length 5.8 and 7.57 mm (FML-CRUST 01275). All collected at type locality (Fig. 1), 18-XII-2013; Col. J. Rodríguez. Additional material: Argentina; 3 males, 7 females Argentina; Salta Province, peatbogs vega Abra de Chorrillos, left branch (VC1C); 24°11’38’’S 66°32’15’’W (Fig. 1). 4358 m a.s.l., 17-XII-2013; Col. J. Rodríguez (FML- CRUST 01277). One female, Argentina, Salta Province, Los Andes Department: 24°13’6.41’’S 66°28’24.09’’W, 4458 m a.s.l., peatbog near to Chorrillos, 18-XII-2013; Col. J. Rodríguez (FML-CRUST 01276, SEM preparations). Diagnosis. Antenna 1 shorter, barely longer than head. Inner plate of maxilla 1 reaching base of palp, with two short and robust pappose setae. Inner plate of maxilla 2 with one robust papposerrate seta. Propodus of male gnathopod 1 hatchet-shaped, with nine serrate setae on inner face, palm angle with three cuspidate setae with accessory seta (one longer external, two shorter, internal). Epimeral plate I rounded, II and III posterodistally slightly acuminate. Etymology. The species epithet “ fatimae “ honors the limnologist Fátima Romero (Fundación Miguel Lillo- Tucumán, Argentina) for her contributions to the study of freshwater macroinvertebrates in Argentina. Habitat. Freshwater, epigean. Description of Holotype male. Size, 8.10 mm. Head smaller than first two thoracic segments combined. Eyes pigmented, large, subrounded. Body surface smooth. Epimeral plate I rounded, different from plates II and III, which are posterodistally slightly acuminate (Fig. 4A). Pereiopodal coxae I to III subequal in shape, slightly overlapping. Acumination in coxae absent. Coxa III narrower than IV. Coxa IV deeper than wide, excavated posteriorly. Posterior lobe of coxa V deeper than anterior lobe. Anterior lobe of coxa VI small (Figs 7A–D). Antenna 1 (Fig. 4B) much shorter than antenna 2 but longer than peduncle of latter; peduncle shorter than head, first segment ⅓ longer than second one, third segment slightly shorter than second; all segments of peduncle with group of simple setae; in addition, second segment with medial plumose seta. Flagellum of eight articles, all with groups of simple setae, additionally 1–2 aesthetascs per article arranged distally between articles 5–7, distal article with group of four long setae and one small simple seta. Antenna 2 (Fig. 4C) less than half of body length, with peduncle slightly longer than head, article 4 shorter than article 5; articles 3–5 with groups of simple setae, and 1–2 plumose setae, article 5 with other simple medial setae. Flagellum with 10 articles, distally with group of simple setae, and some articles with plumose setae. Labrum (Fig. 4D) ventral margin truncate, covered by short distal setules. Mandibles basic amphipodan type (sensu Watling 1993); each with well-developed large, cylindrical, triturative molar. Left mandible (Fig. 4F) incisor 6-denticulate (three short, three long); lacinia 3-denticulate; setal row with five pappose setae. Right mandible (Fig. 4E) incisor 6-denticulate (three very short, three long); lacinia complex, setal row with two pappose setae. Lower lip (Fig. 5A) outer lobes rounded with distal and internal setules, mandibular projection of outer lobes round. Inner lobes wanting Maxilla 1 (Fig. 5B) palp unsegmented, longer than wide, reaching more than half the distance between base of palp and base of setae on outer plate, setulose and with strong papposerrate seta distally; nine serrate long distal setae on outer plate; inner plate slender, shorter than outer one, bearing two apical papposerrate setae; both plates with setules and denticles on outer face. Maxilla 2 (Fig. 5C) plates subequal in length. Inner plate with one strong, long papposerrate seta proximally on inner margin. Both plates sparsely setulose, with apex wearing serrulate, simple, pappose and serrate setae as figured. Maxilliped (Fig. 5D) inner plate apically rounded, longer than wide, with three strong cuspidate setae, apex and margins with setules, pappose and simple setae; outer plate with apical pappose setae continuous with a row of simple setae that cover most of medial margin; outer distal face of both plates with 1–2 short setae; palp longer than outer plate, 4-segmented, second segment longer than wide; inner margins of segments 2 and 3 with several long simple setae; outer distal face of segments 1 and 2 with 1–3 setae; inner distal margin of segment 3 with seven serrate setae; segment 4 unguiform, shorter than segment 3, with thin apical seta shorter than distal nail. Coxal gills on gnathopod 2 (Fig. 6B) to pereiopod 6 (Figs. 7A–C), sac-like. Sternal gills tubular on pereionites II–VII. Gnathopod 1 (Fig. 6A) subchelate. Coxal plate margin with small simple setae. Basis, ischium and merus with serrate setae on posterior margin. Carpus longer than wide, with strong, wide concave posterior lobe, border pectinate and with several serrate setae. Propodus length less than two times maximum width, hatchet-shaped, anterodistal border with group of thin simple setae, inner face with nine serrate setae; denticles of type T1 on postero-distal border; palm slope slightly transverse, margin slightly convex covered with simple setae; palm angle with three cuspidate setae with accessory seta (one longer, external). Dactylus claw-like, inner margin with denticles and three endal setae, outer margin with one thin plumose seta dorsally. Palmar Index (sensu Ruffo 1973) = 0.44. Gnathopod 2 (Fig. 6B) subchelate. Basis approximately 2x longer than wide; posterior margin with five long serrate setae. Basis, ischium and merus each with group of setae on postero-distal border. Posterior lobe of carpus elongated, border pectinate with some serrate setae. Propodus ovate, with scales on postero-distal margin; palm margin slightly longer than posterior margin, with slope slightly oblique, straight and regular with several strong short and medium-length setae; antero-distal border with cluster of thin simple setae; palm angle with two cuspidate setae with an accessory seta. Dactylus claw-like with several endal setae and comb-scales, congruent with palm, with one thin plumose seta dorsally. Palmar Index (sensu Ruffo 1973) = 0.47. Pereiopods 3–4 (Figs. 7A, B) similar in size and shape. Coxal plate of pereiopod 3 longer than wide; coxa of pereiopod 4 excavated posteriorly, deeper than wide; both coxal plates with margins bordered with thin simple setae; posterior margin of basis, ischium, merus, carpus and propodus with simple or cuspidate setae; anterior margin of merus, carpus and propodus with cluster of distal setae; dactylus less than half length of propodus, with one plumose seta. Pereiopods 5–7 (Figs. 7C–E) pereiopod 5 distinctly shorter than 6 and 7, which are subequal in length. Coxal plate of pereiopod 5: wider than long, posterior lobe deeper than anterior; coxa of pereiopod 6: as long as wide, anterior lobe much reduced; coxa of pereiopod 7: wider than long; all coxal plates with thin simple setae on margin. Posterior margin of basis of pereiopods 5–7 expanded (more so in 5 and 7 than in 6) and finely serrate. Anterior margins of basis, merus, carpus and propodus with marginal clusters of 2–6 cuspidate setae; dactylus 5 less than half length of propodus, dactylus 6–7 not reaching half length of propodus, all with a plumose seta. Pleopods (Fig. 8A) all similar, peduncle shorter than rami, biramous; rami multi-annulated and bearing long plumose setae. Uropod 1 (Fig. 8B) peduncle 1.4 times longer than rami, with three proximal cuspidate setae aligned in a longitudinal row and two other distal cuspidate setae; rami subequal in length; outer ramus with two dorsal and four distal cuspidate setae; inner ramus with two dorsal and five distal cuspidate setae (one of them slender); modified curved seta on inner side of inner ramus wanting. Uropod 2 (Fig. 8C) shorter than uropod 1; peduncle subequal to rami, with four cuspidate setae; rami subequal with two proximo-dorsal cuspidate setae; inner ramus of left uropod 2 with four cuspidate setae at the distal end, one of them longer than rest; apex of inner ramus of right uropod 2 with five cuspidate setae; apex of outer ramus with four cuspidate setae (one of them shorter than rest). Uropod 3 (Fig. 8D) much shorter than peduncle of uropod 2; peduncle slightly longer than wide, wider than ramus, with two strong cuspidate distal setae and two other thin simple marginal setae; outer ramus unsegmented, shorter than peduncle, basal width near 1.6 times tip of ramus, apex with three simple setae, and one cuspidate shorter seta. Telson (Figs. 8E, F) wider than long, entire, bearing two widely apart simple setae, symmetrically distributed on distal margin, and with two or three short plumose setae at each side laterally to the simple ones. Females. Measurements: Body length ranging from 3.28 to 7.5 mm; mean body size: 4.59 mm (8 individuals). Habitus similar to male except for the following characters: Antenna 1 flagellum with 5–7 articles. Antenna 2 flagellum with 6–10 articles. Gnathopods 1 and 2 similar to each other in size and shape. Gnathopod 1, inner face of propodus with eight serrate setae (Fig. 6C). Gnathopod 2, inner face of propodus with five serrate setae (Fig. 6D); gnathopod 2 differs from that of the male in shape and smaller propodus. Oostegites subtriangular, with curled setae on the margins (Fig. 6D). Variability in males: Measurements: body length ranging from 5.8 to 9.5 mm; mean body size: 7.8 mm (6 individuals). Some variations were observed in the setae of gnathopod 1 propodus, setae of uropods 2–3, and number of flagellum articles of antennae. Gnathopod 1: some males with seven serrate setae on inner face of propodus (instead of nine). Uropods: in one adult male, peduncle of right uropod 3 with four connate setae (left peduncle with three); another adult male, uropod 3 peduncle with three connate setae, two long and one short, ramus with one simple seta (instead of three). In one adult male, uropod 2 peduncle with four marginal cuspidate setae (two in holotype). Number of articles in antennal flagellum increases with size of the individual, in largest male (9.5 mm) A1 with 10–11 articles, A2 with 13–14 articles; in smallest male (5.8 mm) A1 had only 8 articles and A2 only 10 articles.