Hyalella julia, Mussini & Stepan & Vargas, 2024

Mussini, Giovanni, Stepan, Nicole D. & Vargas, Gersey, 2024, Two new species of Hyalella (Amphipoda, Dogielinotidae) from the Humid Chaco ecoregion of Paraguay, ZooKeys 1191, pp. 105-127 : 105

Hyalella julia sp. nov.

Type material.

Holotype, male (Fig. 7A ), total body length = 8.81 mm, head length = 0.78 mm (CIPLT-O-40); Allotype female (Fig. 7B ), total body length = 5.44 mm, head length = 0.42 mm (CIPLT-O-40). Paraguay, Department of Ñeembucú, Pilar, Yegros Paso field locality (26°51'51"S, 58°16'11"W), September, 06, 2021. Paratypes. 9 males, 20 females (CIPLT-O-40), Yegros Paso field locality (26°51'51"S, 58°16'11"W).

Type locality.

Paraguay, Department of Ñeembucú, Pilar, Yegros Paso field locality (26°51'51"S, 58°16'11"W).

Diagnosis.

Flagella of antennae 1 and 2 with 10-11 and 13-14 articles, respectively. Left mandible incisor toothed, 4-denticulate; left lacinia mobilis 3-denticulate, with short median denticle and two prominent elongated denticles with serrated margin laterally. Gnathopod 2 propodus with palm lacking pronounced cup for dactylus, without papposerrate setae, with cuspidate setae with accessory setae on disto-posterior corner. Pereopod 5 slightly longer than other pereopods. Uropod 1 endopod with a curved seta. Uropod 3 ramus dorsal margin without setae. Uropod 3 peduncle with six simple setae apically. Uropod 3 peduncle longer than wide (rectangular).

Description.

Male (Figs 7 - 11 ). Mean total body length: 7.24 mm; mean head length: 0.76 mm (N = 10). Body surface smooth. Epimeral plates not acuminate. Head smaller than first two thoracic segments, typically gammaridean, rostrum absent. Eyes pigmented, ovoid, located between insertion of antennae 1 and 2 (Fig. 8A ).

Antenna 1 about 3.2 × shorter than body length, 1.3 × shorter than antenna 2, 2.2 × longer than peduncle of antenna 2; peduncle not surpassing head length; flagellum with 10-11 articles, 2.1 × longer than peduncle; aesthetascs occurring distally after article 4 (Fig. 8B ).

Antenna 2 about half of body length; peduncle 1.1 × longer than head; articles 1 to 3 with several simple setae on distal margin, article 3 with several simple setae on lateral margin; flagellum 2.4 × longer than peduncle, with 13-14 articles, with basal article elongated; articles with several simple setae on distal margins; four simple setae apically (Fig. 8C ).

Basic amphipodan mandibles (sensu Watling 1993), without palp; left incisor toothed, 4-denticulate; left lacinia mobilis 3-denticulate, with short median denticle, with two prominent elongated denticles with serrated upper margin laterally. Setal row with four papposerrate setae, molar process large and cylindrical, triturative, with one accessory seta (Fig. 8E ). Right mandible incisor 7-denticulate; lacinia 4-denticulate, setal row with six papposerrate setae (Fig. 8F ).

Upper lip distal margin rounded, covered by several setules on dorsal and ventral faces (Fig. 8D ). Lower lip outer lobes rounded and distally notched, covered distally by several setules on dorsal and ventral faces (Fig. 8G ).

Maxilla 1 inner plate slender, 1.4 × shorter than outer plate, with two apical papposerrate setae and several setules laterally; outer plate with nine serrate setae (Fig. 8H ). Palp short, uniarticulate, 1.2 × longer than wide, with a distal setule, reaching less than half of distance between base of palp and base of setae on outer plate.

Maxilla 2 inner plate 1.1 × longer than outer plate; inner plate with one papposerrate seta and several simple and serrate setae apically, with several setules laterally; outer plate with several simple setae, longest apically, with several setules laterally (Fig. 8I ).

Maxilliped inner plate 1.7 × longer than wide, apically truncated, with three apical cuspidate setae and several simple setae, without comb-scales; outer plate 1.3 × longer than inner plate, apically rounded, with several apical and lateral simple setae; palp 2.3 × longer than inner plate, 1.7 × longer than outer plate, with four articles; article 1 1.3 × longer than wide, with strongly concave distal margin; article 2 1.0 × longer than wide, with inner, outer, and distal margins with several long simple setae; article 3 1.2 × longer than wide, with inner and outer margins with several simple setae; article 4 unguiform, 1.5 × longer than wide, 2.0 × shorter than third article, with distal simple setae, with distal nail and comb-scales absent (Fig. 8J ).

Gnathopod 1 subchelate; coxal plate 1.9 × wider than long; basis with one simple seta on inner margin and one on disto-posterior corner, ischium with few simple setae on disto-posterior corner; merus with several simple setae on posterior margin; carpus 1.5 × longer than wide, 1.2 × longer and 1.2 × wider than propodus, with several simple setae on disto-anterior corner, some with accessory seta, with few simple setae on inner margin, with posterior lobe folded to form scoop-like structure, with pectinate margin with comb-scales, several serrate setae and polygonal pattern; propodus 1.6 × longer than wide, hammer-shaped, with simple seta with accessory seta on anterior margin, with inner margin with several simple setae, with several long simple setae on disto-anterior corner; palm slope transverse, margin slightly concave, with many simple setae, with disto-posterior corner with cuspidate seta with accessory seta; dactylus claw-like, congruent with palm, without comb-scales (Fig. 9A ). Microtrichs present on propodus.

Gnathopod 2 subchelate; coxal plate 1.8 × wider than long; basis with one simple seta on anterior margin and several simple setae on disto-posterior margin; merus with several simple setae on posterior margin; carpus 2.0 × wider than long, with one simple seta on inner margin and two on disto-anterior, with posterior lobe slim produced between merus and propodus, with posterior margin pectinate, with several serrate setae and comb-scales; propodus ovate, 1.4 × longer than wide, with two simple setae on anterior margin; palm subequal to posterior margin of propodus, slope oblique, margin convex, with several long and short simple setae with accessory setae; disto-posterior corner with two cuspidate setae with accessory setae; very shallow cup for dactylus; dactylus claw-like, congruent with palm, without comb-scales (Fig. 9B ).

Pereopods 3 to 7 simple. Pereopods 3 and 4 (Fig. 10A, B ) with posterior margins of merus and carpus with several simple and cuspidate setae; propodus posterior margin with several simple and cuspidate setae; dactylus 2.6 × and 1.9 × shorter than propodus in pereopods 3 and 4, respectively, unguiform. Pereopods 5 to 7 (Fig. 10C-E ) with posterior margins of merus, carpus and propodus with several cuspidate and simple setae; dactylus 2.7 ×, 2.6 ×, and 3.0 × shorter than propodus, respectively, unguiform, with a plumose seta dorsally. Pereopod 3 and 4 of similar sizes, shorter than pereopods 5-7; pereopods 6 and 7 of similar length, pereopod 5 slightly longer than other pereopods.

Pleopods not modified, biramous, elongated; peduncle 4.0 × longer than wide, 1.5 × shorter than mean size of rami, with coupling spines distally; both rami multi-annulated, longer than peduncle; articles decreasing in size distally in both rami; both rami with several plumose setae (Fig. 11A ).

Uropod 1 1.3 × longer than uropod 2; peduncle 1.1 × shorter than outer ramus and 1.2 × shorter than inner ramus, with three cuspidate setae; inner ramus 1.1 × longer than outer ramus, with four cuspidate setae dorsally, and one long curved seta and five cuspidate setae apically; outer ramus with four cuspidate setae dorsally and five cuspidate setae apically (Fig. 11B ).

Uropod 2 1.3 × shorter than uropod 1; peduncle rectangular, 1.0 × shorter than outer ramus and 1.3 × than inner ramus, 2.4 × wider than outer ramus and 1.3 × than inner ramus, with one cuspidate seta dorsally; inner ramus 1.3 × longer than outer ramus, with three cuspidate setae dorsally and three cuspidate setae apically; outer ramus with four cuspidate setae dorsally and four cuspidate setae apically (Fig. 11C ).

Uropod 3 (Fig. 11D ) 1.6 × shorter than peduncle of uropod 1 and 1.1 × than peduncle of uropod 2; peduncle 1.9 × longer than wide, 2.0 × wider than ramus, with six cuspidate setae apically; inner ramus absent; outer ramus uniarticulate, subequal in length to peduncle, with six simple setae apically.

Telson entire, 1.1 × longer than wide, with convex margins, and rounded apically, without setae laterally, and with five cuspidate setae apically (Fig. 2D ).

Coxal gills sac-like present on pereonites 3 to 6; sternal gills tubular and present on pereonites 3 to 7.

Female (Figs 7B , 11E , 12 ). Mean total body length: 5.23 mm; mean head length: 0.46 mm (N = 21).

Antennae similar in shape to male. Antenna 1 flagellum with 10-11 articles. Antenna 2 flagellum with 11-12 articles.

Gnathopod 1 (Fig. 12A ) slightly larger than male gnathopod 1 different from male gnathopod 1 in shape; basis with few simple setae on disto-anterior and posterior margins; ischium with several simple setae on disto-posterior margin; merus with several simple setae on posterior margin; carpus 1.6 × longer than wide, with several serrate setae on disto-anterior corner, posterior lobe with pectinate margin, with comb-scales and one row of serrate setae; propodus 1.8 × longer than wide, hammer-shaped; anterior margin with two simple setae, disto-anterior corner with several simple setae, posterior margin with several simple setae and comb-scales, inner margin with four simple setae; palm slope transverse, margin slightly irregular, slightly concave, with several simple setae, with few simple setae and two long cuspidate setae on disto-posterior corner; dactylus claw-like, with one plumose seta dorsally.

Gnathopod 2 (Fig. 12B ) similar in size and shape to gnathopod 1; basis and ischium with several simple setae on disto-posterior corner; merus with several simple setae on posterior margin; carpus 1.3 × longer than wide, with several simple setae on disto-anterior corner, posterior lobe produced and forming scoop-like structure, pectinate margin with comb-scales, several serrate setae and polygonal pattern; propodus 1.6 × longer than wide, hammer-shaped, with comb-scales on disto-posterior margin, with few simple setae on anterior and posterior margins, with several long simple setae on disto-anterior corner, inner face with several simple setae; palm slope oblique, margin slightly irregular, with several simple setae, disto-posterior corner with two simple and two cuspidate setae; dactylus claw-like, with one plumose seta dorsally.

Telson subequal in length and width, with more convex lateral margins than in male, and with five cuspidate setae, one with accessory seta.

Uropod 1 similar in size and shape to male uropod 1, except for absence of curved seta.

Habitat.

Freshwater, epigean.

Distribution.

Paraguay, Department of Ñeembucú, Pilar. Field locality of Yegros Paso (26°51'51"S, 58°16'11"W).

Etymology.

In honour of the late Don Julio Rafael Contreras, for his seminal studies of Paraguayan biodiversity and generous support of Fundación Para La Tierra.

Taxonomic remarks

Hyalella mboitui sp. nov. and H. julia sp. nov. can be recognised as distinct species based on the taxonomic keys by Damborenea et al. (2020) and morphological differences from other recently described South American species ( Reis et al. 2020; Jaume et al. 2021; Limberger et al. 2021; Rocha Penoni et al. 2021; Talhaferro et al. 2021a, b; Vernica et al. 2022; Waller et al. 2022; Peralta and Verónica 2023; Reis et al. 2023). Both H. mboitui and H. julia show a smooth body without dorsal or lateral processes or mucronations, have pigmented eyes, and lack setae on the dorsal margin of uropod 3. The presence of a curved seta on the ramus of male uropod 1 links both new taxa to a large cluster of South American species spanning Venezuela, Brazil, Chile, Argentina and Uruguay ( Bastos-Pereira and Bueno 2012; Rodrigues et al. 2014; Damborenea et al. 2020; Talhaferro et al. 2021a).

Like H. brasiliensis Bousfield, 1996 from Paraná State (Brazil), both H. mboitui and H. julia lack plumose setae on their telson, but can be readily distinguished from this species by the number of setae on uropods 1 and 2 ( Bousfield 1996; Talhaferro et al. 2021a, b). The presence of six apical setae on the rectangular peduncle of uropod 3 and its rectangular (longer than wide) shape in H. mboitui and H. julia are shared with the Argentinian taxa H. pampeana Cavalieri, 1968 and H. bonariensis Dos Santos, Bond-Buckup & Araujo, 2008, and with H. gauchensis Streck et al., 2017 from Rio Grande do Sul, Brazil ( Damborenea et al. 2020). However, the two Paraguayan species lack the space between the dactylus and the margin of the propodus of male gnathopod 2 characteristics of H. pampeana ( Dos Santos et al. 2008) and differ markedly from H. bonariensis in the pattern and distribution of setae and comb-scales on their limbs and telson, as well as in the numbers of denticles on the mandibular incisor and lacinia mobilis ( Dos Santos et al. 2008). In addition, they differ from H. gauchensis in their mandibular morphology and setal cover of the telson and uropods (cf. Streck et al. 2017).

The two new Paraguayan taxa are also readily distinguishable from recently described Hyalella species from nearby Argentina ( Peralta and Miranda 2019; Vernica and Alejandra 2022) and southern Brazil ( Reis et al. 2020; Limberger et al. 2021; Rocha Penoni et al. 2021; Talhaferro et al. 2021a, b) by the number and type of setae on the telson and uropods 1 and 3 (Figs 5B, D , 11B, D ). Their level of morphological differentiation also indicates that the new Paraguayan species cannot be subsumed under the South American H. curvispina Shoemaker, 1942 species complex, which appears to comprise significant cryptic diversity based on recent molecular marker analyses ( Waller et al. 2022). Despite similarities in telson shape and the morphology and setal cover of maxillae and maxillipeds (Figs 2H-J , 8H-J ; Shoemaker 1942; Grosso and Peralta 1999), H. mboitui and H. julia are distinguished from H. curvispina by their diagnostic mandibular dentition, the absence of a plumose seta on the dactyli of male gnathopods, the number of setae on the telson, and the shape and number of setae of the uropod 3 peduncle, which is wider than long in H. curvispina ( Shoemaker 1942; Grosso and Peralta 1999; Damborenea et al. 2020) but not in H. mboitui and H. julia (Figs 5D , 11C ).

Despite the geographical vicinity of their type locations, H. mboitui and H. julia are separated by clear morphological differences at the level of the gnathopods, uropods and mandibles, as well as by minor differences in the morphology and setal covers of their antennae, maxillae and maxillipeds. Antennae 1 and 2 have fewer articles in their flagellum in H. julia than in H. mboitui : H. julia has minimally 13 articles in antenna 1 and 16 in antenna 2, whereas H. mboitui has minimally 10 in antenna 1 and 13 in antenna 2. The mandibles of the two taxa differ in the number of incisor teeth, with 5 and 6 teeth present in the left mandibles of H. mboitui and H. julia , respectively, and 4 and 7 in their right mandibles. In addition, the left lacinia mobilis of H. julia lacks the distinctive median serrated surface of H. mboitui , and sports instead two prominent, elongated denticles with a serrated edge laterally. The maxillipeds of the two species differ in the number of cuspidate setae on the outer plate and in the shape of palp articles (Figs 2J , 8J ). The male gnathopods of H. julia and H. mboitui differ in the number and type of setae: notably, papposerrate setae are absent in the disto-posterior corner of the gnathopod 2 propodues in H. julia , which shows instead two stout cuspidate setae with accessory setae (Fig. 9B , cf. Fig. 3B ). Papposerrate setae are also present on gnathopod 1 in H. mboitui , but not H. julia (Fig. 9A , cf. Fig. 3A ). In addition, H. julia lacks papposerrate setae on the disto-anterior margin of the gnathopod 1 propodus (Fig. 9A , cf. Fig. 3A ). The propodi of female gnathopods are also more elongated and less subtriangular in H. julia , and differ in the presence and extent of their cover of comb-scales (Fig. 6 , cf. Fig. 12 ). Pereopod 5 is the shortest pereopod in H. mboitui , but the longest in H. julia . Moreover, uropods 1, 2 and 3 in the two species differ in the number of cuspidate setae on their rami and peduncle (Figs 5B, C , 11B, C ).

Habitat and conservation

The geographical vicinity of the two new species and their distinct mandibular morphologies suggest that their differences may stem at least in part from trophic partitioning ( Limberger et al. 2021). Distinct feeding habits may be tied to the different environments characterising the type localities of the two species (Fig. 13 ). Yegros Paso, the type locality of H. julia (Fig. 13B ), falls within a complex of seasonal ponds with relatively stagnant waters bordering on a stream. Locally, water bodies expand and contract in cyclic dry and wet phases depending on rainfall levels ( Hordijk et al. 2023). In contrast, the bodies of water in the type localities of H. mboitui (Ring Road and San Lorenzo; Fig. 13C, D ) are characterised by somewhat stronger riverine influence, with more active flow regimes, and higher availability of macrophytes near the banks. Some distinctions in the morphology of their pleopod setae may suggest corresponding differences in locomotion. Hyalella julia has denser, more strongly developed plumose setae on the pleopods that suggest a higher natatory capacity than in H. mboitui , and may make H. julia better adapted to swimming in lentic habitats ( Streck et al. 2017). In contrast, H. mboitui may predominantly inhabit substrates in its lotic environment or remain near the river bank macrophytes.

The type locality of H. julia is managed for ongoing conservation and research projects on the endangered Pilar tuco-tuco ( Ctenomys pilarensis ). In contrast, major developments are scheduled or currently taking place at the type localities of H. mboitui , San Lorenzo and Ring Road, for the planned construction of flood defences. The connections between the bodies of water inhabited by H. mboitui and H. julia , and their seasonal continuity with the Ñeembucú River, preliminarily suggest that their area extends beyond the type localities. However, Hyalella is known for its high degree of endemism across South America, and the geographic range of different species in the genus is highly variable ( Grosso and Peralta 1999; Streck et al. 2017). To map the ranges of H. mboitui and H. julia , and the degree to which ongoing developments may threaten the species survival, we recommend a wider sampling of freshwater invertebrates in the wetland complex around Pilar and more broadly in the Ñeembucú region.

The discovery of two new crustacean species, collected in a non-targeted impact assessment survey near an urban area, highlights the untapped potential of the Ñeembucú wetlands for biodiversity and conservation research. This ecologically important patchwork of rivers, streams, and flooded grasslands is severely understudied, and its invertebrate fauna remains virtually unexplored amid escalating anthropic impacts ( Dickens et al. 2020; Mereles et al. 2020). More broadly, despite still comprising unfragmented areas of natural habitat, the Humid Chaco ecoregion in Paraguay is under increasing pressure from land use changes, resulting in high and rapid ongoing biodiversity losses ( Mereles et al. 2020). Therefore, taxonomic studies are urgently needed to address the large remaining gaps in the scientific understanding of the region’s biodiversity. Our findings of two undescribed species provide supporting evidence of the potential presence of a significant number of undocumented taxa in the Ñeembucú wetlands, which are likely to benefit from habitat protection measures.

Figures

Figure 2. Hyalella mboitui sp. nov., Department of Neembucu, Paraguay. Paratype, male A habitus B antenna 1 C antenna 2 D upper lip E left mandible, with detail of lacinia and incisor rotated anticlockwise (E 1) and clockwise (E 2) F right mandible, with detail of lacinia and incisor rotated anticlockwise (F 1) and clockwise (F 2) G lower lip H maxilla 1 I maxilla 2 J maxilliped. Scale bars: 1 mm (A); 0.5 mm (B, C); 0.2 mm (D-J); 0.1 mm (E 1, E 2, F 1, F 2).

Figure 3. Hyalella mboitui sp. nov. Paratype, male A gnathopod 1 B gnathopod 2. Scale bars: 0.5 mm.

Figure 5. Hyalella mboitui sp. nov. Paratype, male. A pleopod B uropod 1 C uropod 2 D uropod 3 E male telson F paratype, female telson. Scale bars: 0.5 mm (A-D); 0.2 mm (E, F).

Figure 6. Hyalella mboitui sp. nov. Paratype, female. A gnathopod 1 B gnathopod 2. Scale bars: 0.5 mm.

Figure 7. Hyalella julia sp. nov., Department of Neembucu, Paraguay A holotype, male B allotype, female. Scale bars: 1 mm.

Figure 8. Hyalella julia sp. nov., Department of Neembucu, Paraguay. Paratype, male A habitus B antenna 1 C antenna 2 D upper lip E left mandible with detail of lacinia and incisor rotated anticlockwise (E 1) and clockwise (E 2) F right mandible, with detail of lacinia and incisor rotated anticlockwise (F 1) and clockwise (F 2) G lower lip H maxilla 1 I maxilla 2 J maxilliped. Scale bars: 1 mm (A); 0.5 mm (B, C); 0.2 mm (D-J); 0.1 mm (E 1, E 2, F 1, F 2).

Figure 9. Hyalella julia sp. nov. Paratype, male A gnathopod 1 B gnathopod 2. Scale bars: 0.5 mm.

Figure 10. Hyalella julia sp. nov. Paratype, male A pereopod 3 B pereopod 4 C pereopod 5 D pereopod 6 E pereopod 7. Scale bars: 0.5 mm.

Figure 11. Hyalella julia sp. nov. Paratype, male A pleopod B uropod 1 C uropod 2 D uropod 3 E male telson F paratype, female telson. Scale bars: 0.5 mm (A-C); 0.2 mm (D-F).

Figure 12. Hyalella julia sp. nov. Paratype, female A gnathopod 1 B gnathopod 2. Scale bars: 0.5 mm.

Figure 13. Localities of occurrence for Hyalella mboitui sp. nov. and Hyalella julia sp. nov. in Pilar, southwestern Paraguay A map showing the position of the type localities B-D with scale: 900 m B Yegros Paso C Ring Road D San Lorenzo.