Hyalella rioturbiensis, 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 : 68-78

Hyalella rioturbiensis sp. nov. Isa-Miranda & Peralta

( Figs. 8–13 )

Material examined: Holotype ♂ measuring 8.37 mm, Argentina, Santa Cruz Province, Río Turbio, Arroyo Primavera , altitude: 250 m a.s.l., 51.50715º S, 72.256637º W, 13.XII.2019, S.H. Torres col., water temperature: 9.5°C, electrical conductivity: 130 µS/cm, depth: 10–15 cm ( FML-CRUST 01358 ) . Paratypes: 1 ♀ measuring 5.07 mm ( FML-CRUST 01359 ) , 2 ♀♀ and 6 ♂♂ ( FML-CRUST 01360 ), same data as holotype .

Additional material: Argentina, Santa Cruz Province, Güer Aike, near Río Turbio, Dique , 51°31.907’S, 72°19.225’W, 25.XI.2010, G. Rodríguez col. 3 ♂♂, 3 ♀♀ ( FML-CRUST 01081 ) , 1♂, 3 ♀♀ ( FML-CRUST 01082 ) , 2 ♂♂, 3 ♀♀ ( FML-CRUST 01083 ) .

Type locality: Argentina, Santa Cruz Province, Río Turbio, Arroyo Primavera , 51.50715ºS, 72.256637ºW.

Etymology: The species name is derived from its type locality, Río Turbio.

Habitat: freshwater, epigean on gravel substrate.

Diagnosis: Body smooth. Antenna 2 segment 4 bearing a diagonal row of six plumose (C2) setae. Gnathopod 1 propodus hatched shape, inner face with over 12 serrate setae (F3). Dorsal surface of coxa 4 with tiny plumose setae. Uropod 2 peduncle with a long simple seta on dorsal surface. Peduncle of uropod 3 with three strong setae, one of them flagellate type. Sternal gills present on pereonites 3 to 7. Epimeral plate 1 rounded, plates 2 and 3 slightly acuminate. Uropod 1 not sexually dimorphic, male without modified seta on inner side of inner ramus. Uropod 2 with peduncle slightly shorter than outer ramus. Telson apex with three main setae.

Description of male:

Body stout and smooth. Maximum length observed 8.37 mm. Head: eye rounded, pigmented. Coxae 1–4 slightly overlapping, longer than wide; coxa 1 slightly shorter than coxa 2 and 3, with 5 thin plumose setae on the inner side near the basis insertion; coxa 3 longer than wide and coxa 4 posteriorly excavated, nearly equal in depth and width, with three thin plumose setae on dorsal surface; coxa 5 wider than long, posterior lobe deeper than anterior, coxa 6 as long as wide with much shorter anterior lobe; coxa 7 wider than long; all coxal plates with thin simple setae along margins (type Ia) and microtrichs (type Ib) on surface. Epimeral plate 1 rounded, plates 2 and 3 slightly acuminate.

Antenna 1 ( Fig. 9A ) shorter than Antenna 2 but slightly longer than its peduncle. Peduncular segments 1 –3 with few simple setae and numerous plumose (C2) setae on segment 1. Flagellum consists of ten articles with groups of simple A1 setae and distally positioned aesthetascs between articles 5–9. Type Ib microtrichs on surfaces of peduncle and flagellum.

Antenna 2 ( Fig. 9B ). Peduncle slightly longer than head; peduncular segment 4 much shorter than segment 5, segments 3–5 with distal and medial simple A1 setae and a few isolated plumose (C2) setae, additionally segment 4 has a diagonal row of 6 plumose (C2) setae. Flagellum with 12 articles, each bearing groups of simple setae. Type Ib microtrichs on surfaces of each peduncle and flagellum articles.

Upper lip ( Fig. 9C ) ordinary, with minute setae on the distal part and some projecting pores on the apical surface.

Mandible ( Fig. 10A, B ). Right mandible incisor 8-denticulate, lacinia mobilis complex, setal row with 3 pappose setae; left mandible incisor 7-denticulate (three of them larger), lacinia mobilis 4-denticulate with a row of thin simple setae at base of lacinia mobilis, setal row with five pappose setae. Both mandibles with well-developed triturative molar, accessory seta present.

Lower lip ( Fig. 9D ) ordinary, outer lobes covered with minute setae, apical surface featuring some projecting pores.

Maxilla 1 ( Fig. 10C ). Outer plate with nine serrate type F4 setae; inner plate shorter than the outer, with two apical strong papposerrate setae and several marginal setules. Palp unsegmented, long and narrow, reaching approximately half the distance between the base of the palp and the apex of the outer plate, with a plumose distal seta at the tip.

Maxilla 2 ( Fig. 10D ). Inner plate subequal in length and width to the outer, with two strong pappose setae on the inner margin. Both outer and inner plates with two rows of simple, serrate, and pappose setae apically (see detail drawing).

Maxilliped ( Fig. 10E ). Inner plate longer than wide, apically truncated and with three stout cuspidate B1 setae, additionally with a row of 7 pappose setae medially accompanied by other plumose and simple thin setae distally and externally. Outer plate with mostly serrate setae on inner and distal margins. Palp 4-segmented, segment 4 short and unguiform; segments 1–3 with simple setae at the outer distal end; segment 3 distally and externally ornamented with simple type A1 setae, plumose and serrated type F3 setae.

Gnathopod 1 ( Fig. 11A ) subchelate; basis with two serrate setae on the posterior margin; merus longer than wide, showing a clear scale pattern. Propodus hatchet-shaped, longer than its maximum width, with a group of slender simple setae at the anterodistal corner; inner face with over 12 serrate setae (F3), 11 of which are arranged in an oblique row; palmar margin marked with long and short setae; palm angle equipped with four cuspidate setae, one of them longer, and also with comb/setose scales and 4 long and serrated setae near the group of cuspidate setae; dactylus claw-like, carrying a single thin plumose seta dorsally, with denticles on the inner margin, and tiny simple seta placed close together near distomedial angle of segment, additionally with microtrichs (type Ib). Palmar Index (sensu Ruffo 1973) = 0.46.

Gnathopod 2 ( Fig. 11B ) subchelate; basis with long serrate setae on posterior margin; merus longer than wide, with oblique posterodistal lobe bordered with setae; posterior lobe of carpus with pectinate border lined with a row of serrate setae; propodus ovate, posterior margin less than half the length of the anterior margin, palm margin oblique, with no distinct notch, shorter than the posterior margin, with several strong, short to medium-length setae; palm angle with two cuspidate setae B5 with an accessory seta and without comb/setose scales; dactylus claw-like, carrying a single thin plumose seta dorsally; additionally, type Ib microtrichs are observed on the dactylus and surface of the propodus; palmar index (sensu Ruffo 1973) = 0.47.

Pereiopods 3 and 4 ( Fig. 12A, B ) similar in size and shape; posterior margin of basis of both pereiopods with five plumose setae; posterior margin of merus, carpus, and propodus of P3 and P4 with simple or cuspidate setae and anteroventral angles of merus and carpus with groups of simple and plumose setae; only P3 merus with setae on anterior margin; dactylus short, less than half the length of propodus.

Pereiopods 5–7 ( Fig. 12C–E ). P5 slightly shorter than P6 and 7, with posterior margin of basis expanded and finely serrated; expansion in P7 notably more pronounced than in others; distal margin of expansion in P6 straight; anterior margin of basis of P 5–7 bearing groups of 3–5 plumose setae; margins of ischium, merus, carpus, and propodus with simple or cuspidate setae; dactylus short, similar to Pereiopods 3 and 4.

Coxal gills sacciform ( Fig. 12A–D ), present on gnathopod 2 to pereiopod 6. Sternal gills ( Fig. 12A, B, E ) tubular, present on pereonites 3 to 7.

Pleopods ( Fig. 13A ) biramous and similar in structure; peduncle shorter than rami, with retinacula and two thin simple setae; rami multi-annulated, bearing long plumose setae.

Uropod 1 ( Fig. 13B ). Peduncle longer than rami, with four cuspidate setae on the dorsal surface aligned in a longitudinal row, additionally with other two distal cuspidate setae; outer ramus somewhat longer than the inner, with two dorsal and seven distal cuspidate setae, and one additional seta on ventral surface; inner ramus with three dorsal and four distal cuspidate setae, without a modified curved seta on the inner side; microtrichs type Ib on peduncle and rami.

Uropod 2 ( Fig. 13C ) shorter than uropod 1, with peduncle slightly shorter than outer ramus; peduncle features three dorsal cuspidate setae aligned in a row, along with additional setae on dorsolateral and dorsomedial distal margin, and a long simple seta on dorsal surface with a scale pattern extending across its entire length; rami with two dorsal cuspidate setae, additionally inner ramus with three and outer with four distal cuspidate setae; microtrichs type Ib on peduncle and rami.

Uropod 3 ( Fig. 13E, F ) shorter than the peduncle of uropod 2; peduncle much wider than the ramus, as long as wide, with four strong distal setae including one modified flagellate seta, microtrichs type Ib cover entire peduncle; ramus stout, shorter than the peduncle, with the apex bearing one strong cuspidate seta and six simple setae.

Telson ( Fig. 13D ) wider than long, entire, apically rounded, bearing three main simple setae asymmetrically arranged, additionally, two short plumose setae are positioned subdistally on each side of dorsal surface; dorsal surface exhibits a scale pattern and type Ib microtrichs.

Female (paratypes): Maximum body length observed 5.07 mm. Habitus similar to male except for the following characters: gnathopods 1 and 2 closely resemble each other in size and shape. Gnathopod 2 differs from its male counterpart in both shape and the relatively smaller size of its propodus, with the inner face displaying six serrate setae; palm angle with three cuspidate setae B5 with an accessory seta; dactylus with four simple setae placed close together near the distomedial angle of the segment, two of which are longer ( Fig. 11C 2 ). Oostegites subtriangular, with curled setae on the margins ( Fig. 11C 1 ).

Remarks. Hyalella rioturbiensis sp. nov. shares similarities with the Hyalella patagonica complex but is morphologically distinct from H. patagonica . The propodus of male gnathopod 2 is ovate in Hyalella rioturbiensis sp. nov., whereas it is more rectangular in H. patagonica . Additionally, the telson of H. rioturbiensis sp. nov. bears three main thin setae and two smaller simple setae, whereas H. patagonica has more than ten minute setae.

When compared to Hyalella franciscae , H. rioturbiensis sp. nov. differs in both the morphology and setation 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 cuspidate setae. In contrast, H. rioturbiensis sp. nov. has an ovate propodus, a palm margin shorter than the posterior margin, and two cuspidate setae on the palm angle. Additionally, H. franciscae possesses a long ramus on uropod 3, where the ramus and peduncle are of equal length, whereas H. rioturbiensis sp. nov. has a stouter ramus that is shorter than the peduncle.

A key distinguishing feature of H. rioturbiensis sp. nov. is the presence of two strong pappose setae on the inner margin of the inner plate of maxilla 2, whereas H. franciscae and H. domuyo sp. nov. have only one. Hyalella domuyo sp. nov. and H. rioturbiensis sp. nov. share the presence of a seta on dorsal surface of the peduncle of uropod 2. Additionally, H. rioturbiensis sp. nov. features flagellate setae on the peduncle of uropod 3, marking the first report of this seta type in Hyalella .

Figures

FIGURE 1. Map of Argentina showing the geographic distribution of the 16 known species of Hyalella, including the two newly described species, Hyalella domuyo sp. nov. and Hyalella rioturbiensis sp. nov.

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

FIGURE 8. Hyalella rioturbiensis sp. nov., habitus. A, holotype male (FML-CRUST 01358); B, paratype female (FML- CRUST 01359). Scale bars: 1 mm.

FIGURE 9. Hyalella rioturbiensis sp. nov., holotype male (FML-CRUST 01358). A, antenna 1; A1, arrow showing detail of the apex of article 8; B, antenna 2; C, upper lip; D, lower lip. Scale bars: 0.1 mm (A–D), 0.05 mm (A1).

FIGURE 10. Hyalella rioturbiensis sp. nov., holotype male (FML-CRUST 01358). A, right mandible; B, left mandible; C, maxilla 1; D, maxilla 2, arrows indicating details of setae from the plates; E, maxilliped. Scale bars: 0.1 mm.

FIGURE 11. Hyalella rioturbiensis sp. nov., holotype male (FML-CRUST 01358) and paratype female (FML-CRUST 01359). A, male gnathopod 1; A1, arrow indicating details of the palmar angle; B, male gnathopod 2; C1, female gnathopod 2; C2, female propodus and dactylus of gnathopod 2, arrow indicating detail of the cuspidate seta on the palmar angle. Scale bars: 0.2 mm (A, B), 0.1 mm (C1), 0.05 mm (A1, C2).

FIGURE 12. Hyalella rioturbiensis sp. nov., holotype male (FML-CRUST 01358). A, pereiopod 3; B, pereiopod 4, arrow indicating detail of setae on the surface of the coxa; C, pereiopod 5; D, pereiopod 6; E, pereiopod 7. Scale bars A–E: 0.2 mm.

FIGURE 13. Hyalella rioturbiensis sp. nov., holotype male (FML-CRUST 01358). A, pleopod 1 and epimeral plate 1; B, uropod 1; C, uropod 2; D, telson; E, uropod 3; E1, arrow indicating detail of flagellate seta; F, optical microscopy image of the flagellate seta. Scale bars: 0.1 mm (A–E), 0.05 (E1, F).

FIGURE 15. Propodus of male gnathopod 2.