Hyalella domuyo, Isa-Miranda & Peralta & Martin & Torres, 2025

Isa-Miranda, Águeda Verónica, Peralta, Marcela, Martin, Juan Pablo & Torres, Santiago Hernán, 2025, Freshwater Amphipod Crustaceans of Patagonia, Argentina: Two New Species of Hyalella Smith, 1874 with an Identification Key for the Genus, Zootaxa 5637 (1), pp. 57-82 : 60-68

Hyalella domuyo sp. nov. Isa-Miranda & Peralta

( Figs. 2–7 )

Material examined: Holotype ♂ measuring 9.51 mm, Argentina, Neuquén Province, Área Natural Protegida Sistema Domuyo, Arroyo Aguas Calientes , altitude: 1841 m a.s.l., 36.68914º S, 70.609943º W, 07.II.2023, M. Paz col., water temperature: 22.3°C, depth: 3–5 cm ( MPCN-Crus-003 ). Paratypes: 1 ♀ measuring 5.76 mm ( MPCN-Crus-002 ), 1 ♂ measuring 6.23 mm ( MPCN-Crus-001 ), same data as holotype.

Type locality: Argentina, Neuquén Province, Área Natural Protegida Sistema Domuyo, Arroyo Aguas Calientes , altitude: 1841 m a.s.l, 36.68914º S, 70.609943º W.

Etymology: The species name (noun in apposition) is in reference to the type locality, Domuyo. It comes from the Mapudungun language spoken by the Mapuche people and means ‘the one that smokes and roars’.

Habitat: freshwater, epigean on rocky substrate.

Diagnosis: Body smooth. Antenna 2 much longer than Antenna 1. Mx 1 palp unsegmented, long and narrow, with a simple distal seta at the tip. Gnathopod 1 propodus hatched shape, inner face with an oblique row of ten serrate setae (type F3). Pereopod 4 coxa with a thin serrate seta in the posterior cavity. Pereopod 7 basis with three short setae placed subdistally on the outer surface. Epimeral plate 1 rounded, plates 2 and 3 slightly acuminate. Uropod 1 not sexually dimorphic, male without modified seta on inner side of the inner ramus. Dorsal surface of Uropod 2 peduncle with a long serrate seta. Apex of telson with many simple setae (more than ten). Sternal gills in pereonites 3 to 7.

Description of male:

Body stout and smooth. Maximum length observed 9.51 mm. Head: eye ellipsoid, pigmented. Coxae 1–4 slightly overlapping, longer than wide; coxa 1 slightly shorter than 2 and 3; coxa 3 narrower than 4; coxa 4 posteroventrally excavated, with a thin serrate seta along the excavation margin; coxa 5 posterior lobe longer than anterior; coxa 6 anterior lobe small; coxa 7 wider than long; all coxal plates with microtrichs (type Ia) along the margin, and microtrichs (type Ib) on the surface. Epimeral plates 1 rounded, plate 2 and 3 slightly acuminate.

Antenna 1 ( Fig. 3A ) much shorter than Antenna 2 but slightly longer than its peduncle. Peduncle A1 shorter than head, all peduncular segments with simple and plumose (C2) setae, besides type Ib microtrichs. Flagellum consists of nine articles all with groups of simple A1 setae and type Ib microtrichs; additionally, 1–2 aesthetascs distally positioned on articles 2 –8.

Antenna 2 ( Fig. 3B ) peduncle slightly longer than head; glandular cone, distal part of canal with irregular margins; segment 4 much shorter than 5, segments 3 –5 with groups of distal and medial simple A1 setae, additionally with another plumose (C2) setae. Flagellum with 13 articles, each bearing groups of simple setae and type Ib microtrichs.

Upper lip ( Fig. 3C ) ventral margin slightly rounded with minute setae on the distal part.

Mandible ( Fig. 4A, B ). Right mandible incisor 8-denticulate (three distal long, five proximal short); lacinia complex with multi-denticles; setal row with 4 pappose setae; left mandible incisor 6-denticulate (two distal long, four proximal short), lacinia mobilis 5-denticulate; setal row with five pappose setae, accesory setae present. Both mandibles with well-developed large, cylindrical, triturative molar, accessory seta present.

Lower lip ( Fig. 3D ). Outer lobes rounded covered with minute setae, apical surface with projected pores, mandibular projection of outer lobes rounded with microsetae.

Maxilla 1 ( Fig. 4C ). Outer plate with nine serrate type F4 setae; inner plate shorter than the outer, with two apical papposerrate setae and several marginal setules. Palp unsegmented, narrow with a slight constriction in the distal third, length reaching more than half the distance between the base of the palp and the apex of the outer plate, with a simple distal seta at the tip.

Maxilla 2 ( Fig. 4D ). Inner plate subequal in length and wide to the outer and with one strong pappose seta proximally on the inner margin; both plates bear serrate, simple and pappose setae and few setules.

Maxilliped ( Fig. 4E ). Inner plate longer than wide, with three stout apical 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 segment wider than long, fourth segment much shorter than segment 3 and unguiform; all segments with simple setae at the outer distal end, additionally segment 2 with a long subdistal serrate seta on dorsal surface close to the inner margin, segment 3 distally ornamented with both simple type A1 setae and serrated type F3 setae.

Gnathopod 1 ( Fig. 5A, B ) subchelate. Basis with four serrate setae on the posterior margin. Propodus hatchet-shaped, longer than its maximum width, with a group of slender simple setae at the anterodistal border; inner face with an oblique row of ten serrate setae (type F3); palmar margin marked with shallow serrations; palm angle equipped with four cuspidate setae, one of them longer and with comb/setose scales; dactylus claw-like, carrying a single thin plumose seta dorsally, with denticles on the inner margin; additionally, microtrichs (type Ib) on dactylus and propodus. Palmar Index (sensu Ruffo 1973) = 0.37.

Gnathopod 2 ( Fig. 5C ) subchelate. Basis with seven long serrate setae on the posterior margin. Posterior lobe of carpus with pectinate border lined with row of serrate setae. Propodus ovate, palm margin slightly concave, shorter than the posterior margin, with several strong, short to medium-length setae; palm angle with two cuspidate setae B5 one of them longer, both setae with an accessory seta; dactylus claw-like, carrying a single thin plumose seta dorsally, along with a series of denticles; additionally, microtrichs type Ib are observed on dactylus and propodus. Palmar Index (sensu Ruffo 1973) = 0.44.

Pereiopods 3 and 4 ( Fig. 6A, B ) similar in size, shape and quetotaxy; merus, carpus, and propodus with setae on posterior margin and distal angles; posterior margin of basis with four and two groups of setae on P3 and P4 respectively; dactylus short, less than half the length of propodus.

Pereiopods 5–7 ( Fig. 6C–F ). P5 notably shorter than P 6–7, which are subequal in length; basis: P 5–7 posterior margin expanded, P7 basis notably more expanded than P 5–6; thin simple setae (type A10) on posterior margin of basis P 5–7, additionally, only basis of Pereiopod 7 with three setae, subdistally on outer surface; anterior margin of basis, ischium, merus, carpus and propodus of P 5–7 bearing groups of simple or cuspidate setae; dactylus short, similar to Pereiopods 3 and 4.

Coxal gills ( Fig. 6A–D ) sacciform, present on gnathopod II to pereiopod 6. Sternal gills tubular, present on pereonites 3 to 7.

Pleopods ( Fig. 7A ) all biramous and similar in structure; peduncle shorter than rami, with retinacula, two thin plumose setae and microtrichs; rami multi-annulated and bearing long plumose setae.

Uropod 1 ( Fig. 7B ). Peduncle 1.3 times longer than rami, with five cuspidate setae on dorsal surface aligned in a longitudinal row, and other distal cuspidate seta; microtrichs type Ib present on peduncle and rami; outer ramus slightly longer than the inner, with two dorsal and six distal cuspidate setae, only one longer, additionally, other seta on ventral surface; inner ramus with three dorsal and four distal cuspidate setae, without curved setae on inner side.

Uropod 2 ( Fig. 7C ) shorter than uropod 1; peduncle slightly longer than rami, with two long and thin setae on dorsal surface and margin and three other cuspidate setae longitudinally aligned, additionally other cuspidate distal seta and microtrichs type Ib; outer ramus with two dorsal and four distal cuspidate setae, only one longer; inner ramus with two dorsal and three distal cuspidate setae, one longer than rest.

Uropod 3 ( Fig. 7D ) shorter than peduncle of uropod 2; peduncle much wider than ramus, as long as wide, with seven strong cuspidate distal setae and four thin and short plumose setae on ventral face; ramus stout, shorter than peduncle, with apex bearing one strong cuspidate seta and other thin six simple setae; microtrichs type Ib present on peduncle and rami.

Telson ( Fig. 7E ) maximum width slightly greater than maximum length, entire, with 13 thin setae asymmetrically distributed on the apical margin; three short plumose setae are positioned subdistally on each side of dorsal surface; additionally exhibits a scale pattern and microtrichs type Ib on all dorsal surface.

Female (paratypes): Maximum body length observed 5.76 mm. Habitus similar to male except for the following characters: gnathopods 1 and 2 closely resemble each other in size and shape, particularly similar to male gnathopod 1. However, gnathopod 2 differs from its male counterpart in both shape and size, being relatively smaller and possessing five serrate setae ( Fig. 5D, E ) on its inner face of propodus. Oostegites subtriangular, without curled setae on the margins, indicating an apparently incompletely developed oostegite ( Fig. 5D ).

Remarks. This species is closely related to Hyalella patagonica and Hyalella franciscae , both of which belong to the Hyalella patagonica complex ( González & Watling 2003). Hyalella domuyo sp. nov. primarily differs from H. patagonica in having a broader propodus on male gnathopod 2 (versus a more rectangular shape in H. patagonica ), seven robust setae on the peduncle of uropod 3 (versus four), and a plumose seta near the excavation of coxa 4 (absent in H. patagonica ). Additionally, the telson of H. patagonica bears more than ten moderately long and slender simple setae at the apex, whereas in H. domuyo sp. nov., only minute setae are present.

Compared to H. franciscae , H. domuyo sp. nov. exhibits a distinct morphology of male gnathopod 2 ( Fig. 15 ). In H. franciscae , the propodus is triangular, the palm margin is equal in length to the posterior margin, and the palm angle lacks setae. In contrast, H. domuyo sp. nov. has an ovate propodus, a palm margin shorter than the posterior margin, and two setae on the palm angle. Additionally, H. franciscae possesses a long ramus on uropod 3, with the ramus and peduncle being of equal length, whereas in H. domuyo sp. nov., the ramus is stout and shorter than the peduncle. The rami of uropod 1 in H. franciscae bear 4–5 lateral setae, while in H. domuyo sp. nov., they bear only 2–3. A distinguishing feature of H. domuyo sp. nov. is the presence of a long, fine, and serrate seta on the peduncle of uropod 2, which is absent in H. franciscae .

Figures

FIGURE 2. Hyalella domuyo sp. nov., habitus. A, paratype female (MPCN-Crus-002); B, holotype male (MPCN-Crus-003). Scale bars: 1 mm.

FIGURE 3. Hyalella domuyo sp. nov., holotype male (MPCN-Crus-003).A, antenna 1; B, antenna 2; B1, arrow indicating the structure and detail of the glandular cone; C, upper lip; D, lower lip. Scale bars: 0.05 mm (B1), 0.1 mm (A–D).

FIGURE 4. Hyalella domuyo sp. nov., holotype male (MPCN-Crus-003).A, left mandible; B, right mandible; C, maxilla 1; C1, distal part of the outer plate of maxilla 1; D, maxilla 2; E, maxilliped. Scale bars: 0.1 mm.

FIGURE 5. Hyalella domuyo sp. nov., holotype male (MPCN-Crus-003) and paratype female (MPCN-Crus-002). A, male gnathopod 1; B, male propodus and dactylus of gnathopod 1; B1, arrow indicating details of the palmar angle; C, male propodus and dactylus of gnathopod 2; D, female gnathopod 2; E, female propodus and dactylus of gnathopod 2. Scale bars: 0.05 mm (B1), 0.2 mm (C), 0.1 mm (A, B, D, E).

FIGURE 6. Hyalella domuyo sp. nov., holotype male (MPCN-Crus-003). A, pereiopod 3; B, pereiopod 4; C, pereiopod 5; D, pereiopod 6; E, pereiopod 7; F, picture showing detail of microtrichs (type Ib) on coxae of pereiopods. Scale bars: 0.2 mm (A–E), 0.05 (F).

FIGURE 7. Hyalella domuyo sp. nov., holotype male (MPCN-Crus-003). A, pleopod 1; B, uropod 1; C, uropod 2; D, uropod 3; E, telson. Scale bars: 0.1 mm.

FIGURE 15. Propodus of male gnathopod 2.