Hyalella oscari Isa-Miranda, Peralta, González & Nieto, 2025, sp.n.

Hyalella oscari sp.n. Figs 2–7. Hyalella sp. 6 — Hankel et al., 2023 MATERIAL EXAMINED. Holotype. Argentina: 1 ♂, Catamarca Province, Calalaste, – 25.70791° S – 67.52827° W, alt. 4429 m a.s.l, 16.X.2020, J. Rodriguez leg., (FML-CRUST 01337), 9.6 mm. Paratypes: 1 ♀ measuring 6.18 mm, and 2 ♂♂ and 1 ♀ (FML-CRUST 01338), 2 ♂♂ and 2 ♀♀ (IBN-EcoPP-25D), same data as holotype. Additional material: Argentina: 5 ♂♂ and 4 ♀♀, La Rioja Province, Río Los Baños, – 28.1725° S – 69.17408° W, 3915 m a.s.l., 24.II.2016, 3 ♂♂ and 2 ♀♀, Catamarca Province, Quebrada del Diablo, – 26.02902778° S – 67.69330556° W, 3955 m a.s.l, 15. V.2017, 3 ♂♂, Calalaste, – 25.7135° S – 67.52336° W, 4392 m a.s.l, 15.XII.2015, J. Rodriguez leg. DIAGNOSIS. Body smooth.Antenna II slightly longer than head and longer than Antenna I. Maxilla I palp with a medial constriction and with two plumose setae on tip. Gnathopod I propodus with sinuous palm margin exhibiting slight medial concavity; palm angle with four cuspidate setae. Two short setae placed subdistally on outer surface of basis of pereiopod 7. Sternal gills present on pereonites 3 to 7. Epimeral plate 1 rounded, plates 2 and 3 slightly acuminate. Uropod 1 not sexually-dimorphic. TYPE LOCALITY AND REFERENCE SEQUENCES. Calalaste peatbog, – 25.70791° S – 67.52827° W, 4429 m a.s.l, Catamarca Province, Argentina. GenBank accession numbers: COI: OR726343, OR726347, OR726345, OR726346 (Fig. 1). ETYMOLOGY. The species was named in honour of the first author’s grandfather. DESCRIPTION OF MALE Body: Stout and smooth. Maximum length observed 9.78 mm. Head: Eye ellipsoid, pigmented. Antenna I: shorter than antenna II but slightly longer than its peduncle. Peduncular segments 1-3 with few simple setae and numerous plumose setae C2, alongside microsetae (Ib type). The flagellum consists of nine articles with groups of simple setae A1, additionally featuring distally positioned aesthetascs, occurring between articles 5–7 (Fig. 3 a, b). Antenna II: longer than Antenna I, with its peduncle approximately equal to the length of the head. Peduncular segment 4 much shorter than 5. Peduncular segment 3 with a plumose thin seta; segments 3–5 with distal and medial simple A1 or plumose setae C2. Flagellum comprises 11 articles, each bearing groups of simple setae (Fig. 3 c, d). Upper lip: ordinary, with minute setae on the distal part (Fig. 4 a). Mandible: Right mandible incisor 6-denticulate, lacinia mobilis complex bifurcate, setal row with 4 pappose setae (Fig. 4 b). Left mandible incisor 5-denticulate, lacinia mobilis 4-denticulate, setal row with six pappose setae (Fig. 4 c). Both mandibles with well-developed triturative molars. Lower lip: ordinary, outer lobes covered with minute setae (Fig. 4 d). Maxilla I (Fig. 4 e): palp unsegmented, long and narrow, with a medial constriction, reaching more than half the length of the distance between the base of the palp and the apex of the outer plate, with two plumose distal setae on tip. Outer plate with nine serrate setae type F4, some of them larger and spatulate, as can be observed in detail in the SEM image (Fig. 4 e). Inner plate shorter than outer one, with two apical papposerrate setae, and several marginal setules. Maxilla II (Fig. 4 f): Inner plate subequal in length to the outer with 1 strong pappose seta on inner margin; outer and inner plates with few hair-like setae. Maxilliped (Fig. 4 g): Inner plate longer than wide, with three stout robust cuspidate B1 setae, accompanied by additional pappose setae and setules on both apex and margins. Outer plate with simple setae on inner and distal margins. Palp 4-segmented, second one as long as wide; segment 4 short and unguifom; segments 1–3 with simple setae at outer distal end; segment 3 distally ornamented with denticles of type t5, featuring setae of both simple type A1 and serrated type F3. Gnathopod I (Fig. 5 a): subchelate. Coxal plate longer than wide, with microtrichs (type Ia) along margin. Basis with four simple setae on posterior margin. Propodus (Fig. 5 b) hatchetshaped, longer than its maximum width, with group of slender simple setae at anterodistal corner; inner face with oblique row of seven serrate setae (F3) arranged in two groups; palmar margin sinuous; palm angle equipped with four cuspidate setae and comb/setose-scales. Dactylus claw-like, with denticles on the inner margin. Additionally, microtrichs of type Ib are observed on the dactylus and surface of the propodus. Palmar Index (sensu Ruffo [1973]) = 0.49. Gnathopod II (Fig. 5 c): subchelate. Basis approximately three times longer than its maximum width, bearing four groups of setae at posterior margin. Basis, ischium and merus each with group of setae on postero-distal angle. Posterior lobe of carpus with pectinate border lined with row of serrate setae. Propodus ovate; palm margin oblique, slightly longer than posterior margin; palm margin with several strong, short to medium-length setae; palm angle with two cuspidate setae B5 with accessory seta and comb/setose scales. Dactylus claw-like, congruent with palm, carrying single thin plumose seta dorsally. Palmar Index (sensu Ruffo [1973]) = 0.34. Pereiopods 3 and 4 (Fig. 6 a, b): similar in size and shape. Coxal plates: pereiopod 3 longer than wide; pereiopod 4 excavated posteriorly, longer than wide; both coxal plates with margins lined with thin simple setae (type Ia); posterior margin of basis, merus, carpus and propodus with simple or cuspidate setae; dactylus short, less than half length of propodus. Pereiopods 5–7 (Fig. 6 c–e): pereiopod 5 notably shorter than pereiopods 6 and 7, which are subequal in length. Coxal plates: pereiopod 5: wider than long, posterior lobe deeper than anterior; pereiopod 6: as long as wide with a significantly reduced anterior lobe; pereiopod 7: wider than long; all coxal plates with thin, simple setae along their margins (type Ia). Basis: posterior margin expanded, notably more in pereiopod 7 than in pereiopods 5 and 6, finely serrated; additionally, the seventh pereiopod has two reduced setae subdistally on outer surface; anterior margin of basis of pereiopod 5 bearing group of four plumose setae. Anterior and posterior margins of ischium, merus, carpus, and propodus with simple or cuspidate setae. Dactylus short, like pereiopods 3 and 4. Coxal gills: sacciform, present on gnathopod II to pereiopod 6 (Fig. 6 a–d). Sternal gills tubular (Fig. 6 d), present on pereonites 3 to 7. Pleopods: Biramous, similar; peduncle shorter than rami, with retinacula; rami multi-annulated and bearing long plumose setae. Uropod 1 (Fig. 7 a): Peduncle longer than rami, with four proximal cuspidate setae on dorsal surface and two other distal cuspidate setae all aligned in a longitudinal row; rami subequal in length; outer ramus with three dorsal and four distal cuspidate setae; inner ramus with two dorsal and five distal cuspidate setae, without modified curved seta on inner side. Microtrichs of type Ib on both peduncle and rami. Uropod 2 (Fig. 7 b): shorter than uropod 1. Peduncle longer than rami, with three dorsal cuspidate setae aligned in a longitudinal row and other cuspidate setae on dorsolateral and dorsomedial distal margin; inner ramus with two dorsal and six distal cuspidate setae, one of them longer than rest; outer ramus with one dorsal and three distal cuspidate setae, one of them longer than rest. Microtrichs of type Ib on peduncle and rami. Uropod 3 (Fig. 7 c): shorter than peduncle of uropod 2. Peduncle much wider than ramus, as long as wide, with five strong cuspidate distal setae and other six thin simple setae on ventral face; ramus stout, shorter than peduncle, apex with one simple seta and five strong cuspidate setae. Telson (Fig. 7 e): wider than long, entire, with many thin simple setae on distal margin and microtrichs type Ib; dorsal surface with a scale pattern. The telson of a male paratype features only two simple setae at each side (Fig. 7 d). Epimeral plates (Fig. 7 f): Plate 1 is rounded posterodistally, while Plates 2 and 3 are slightly acuminate; all posterior margins bear a few setules. Intraspecific Variability in males: some males (IBN-EcoPP-23C) exhibit six setae on the inner face of gnathopod I propodus, while others display nine, in contrast to the seven displayed by the holotype. Variability was observed also in the setae count at telson and uropod 2 apices; in one of the male paratypes (FML-CRUST 01338), the telson exhibited only two simple setae on each side (Figs. 7 d, e), while the inner ramus of uropod 2 apex carries seven setae. FEMALE (PARATYPES). Maximum body length observed 7.76 mm. Habitus similar to male except for the following characters: palp of maxilla I shorter, with two significantly longer setae at apex compared to male (Fig. 4 e). Gnathopods I and II closely resemble each other in size and shape, inner face of gnathopod I displaying seven serrate setae, while gnathopod II features six. Gnathopod II differs from its male counterpart in both shape and the relatively smaller size of its propodus (Fig. 5 d, e). Oostegites broad and subtriangular, with larger curled setae on the margins (Fig. 5 d).