Hyalella terrasolis, Castiglioni, Limberger & Santos, 2025

Limberger, Márcio, Castiglioni, Daniela Da Silva & Santos, Sandro, 2025, Hyalella terrasolis, a new epigean species of freshwater amphipod (Crustacea, Peracarida, Hyalellidae) from southern Brazil, Zootaxa 5609 (1), pp. 97-115 : 98-112

publication ID	https://doi.org/10.11646/zootaxa.5609.1.6
publication LSID	lsid:zoobank.org:pub:092B2DDA-07C1-49C6-96F8-E911EF3BABDC
DOI	https://doi.org/10.5281/zenodo.15225074
persistent identifier	https://treatment.plazi.org/id/FD1A87D8-FF9D-FFCA-8BD5-5A05FCE626BB
treatment provided by	Plazi
scientific name	Hyalella terrasolis
status	sp. nov.

Treatment

Hyalella terrasolis sp. nov. Castiglioni, Limberger & Santos

Figures 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8

Type locality: Granja Terra do Sol , municipality of Palmeira das Missões, state of the Rio Grande do Sul, southern Brazil (27°59'17.0"S – 53°13'04.0"W) ( Fig. 1A, 1B, 1C View FIGURE 1 ) GoogleMaps .

Habitat: Freshwater epigean. Small pond with approximate dimensions of 100 m ² and a central depth of two meters. The location is characterized by having 90% of its total area covered by grass vegetation and receives water resources from a spring located approximately 100 meters away. This pond is part of the watershed of the Várzea River, situated at an altitude of 541 meters above sea level. In a predominantly agricultural region, it is surrounded by soybean, wheat, and corn fields ( Figs. 1A, B, C View FIGURE 1 ).

Type specimens. Holotype: male, body length = 7.93 mm; head length = 0.84 mm ( Fig. 2A View FIGURE 2 ) ( MNRJcarcino 31353 ), Granja Terra do Sol , municipality of Palmeira das Missões (27°59’17.0”S – 53°13’04.0”W) ( Figs. 1A, 1B, 1C View FIGURE 1 ), May 21, Limberger, M. & Castiglioni, D.S. cols GoogleMaps . Allotype: female, body length = 5.86 mm, head length = 0.62 mm ( Fig. 2B View FIGURE 2 ) ( MNRJcarcino 31354 ), same date and locality of the holotype GoogleMaps . Paratypes: ( MNRJcarcino 31355 ), 20 whole specimens (10 males and 10 females); GoogleMaps ( CLTA 220 ), 48 whole specimens (23 males, eight females, seven ovigerous females and ten juveniles), and five males and three females on slides (same data and locality of the holotype) GoogleMaps .

Diagnosis. Body surface smooth. Eyes ovoid and pigmented. Antenna 1 shorter than antenna 2. Maxilla 1 with palp uniarticulate, not reaching half of the distance between the base of palp and base of the setae of the outer plate. Inner plate of maxilla 2 with two papposerrate setae (one slightly smaller). Gnathopod 1 propodus hammer-shaped, longer than wide with five serrate setae with accessory setae and seven simple setae on inner face, comb scales on distoanterior and distoposterior border, and carpus with a posterior lobe with pectinate border. Gnathopod 2 propodus ovate with a very pronounced posterior lobe covered by comb scales and carpus with a posterior lobe with pectinate border. Uropod 1 with a curved seta on inner ramus. Uropod 3 with peduncle rectangular and with 9–10 cuspidate setae with accessory seta. Telson as long as wide (square) with ten cuspidate setae with accessory setae. Sternal gills on pereonites 2 to 7.

Description of male (paratypes). Mean body length: 6.46 ± 0.54 mm (n = 10), mean head length = 0.69 ± 0.05 mm (n = 10). Body surface smooth. Epimeral plate not acuminated. Head slightly smaller than the first two thoracic segments. Eyes rounded and pigmented. ( Fig. 3A, 3A View FIGURE 3 1 View FIGURE 1 ).

Antenna 1 ( Fig. 3B View FIGURE 3 ) peduncle with three articles; first article longer than wide and slightly longer than third, first article with cuspidate setae on distal margin; flagellum with 12–13 articles, all with group of three or four simple setae apically. Aesthetascs in articles four to twelve.

Antenna 2 ( Fig. 3C View FIGURE 3 ) surpassing half of the body length; peduncle longer than head length; flagellum consisting of 15 to 16 articles of similar size, with group of three simple setae apically.

Basic amphipodan mandible type (in sensu of Watling 1993) with palp absent. Right mandible ( Fig. 3D View FIGURE 3 ) incisor process with five teeth and two pappose setae with group of setules. Left mandible ( Fig. 3E View FIGURE 3 ) incisor process and lacinia mobilis with five teeth; three pappose setae under lacinia mobilis. Both mandibles with molar process cylindrical, large and triturative, superior margin with setules, inner margin with one long pappose setae.

Upper lip ( Fig. 3F View FIGURE 3 ) with rounded borders and presence of several simple setae and setules; ventral margin with many setules.

Lower lip ( Fig. 3G View FIGURE 3 ) bilobed, with distal margins ovoid with many simple setae and setules on inner and distal margins, outer margin smooth.

Maxilla 1 ( Fig. 3H View FIGURE 3 ) palp short and unarticulated, thin apically with setules, length not reaching half of distance between the base of palp and base of setae on outer plate; inner plate slender, 1.7x shorter than outer plate with two apical papposerrate setae and some simple setae on outer margin; outer plate with nine serrate setae distributed apically.

Maxilla 2 ( Fig. 3I View FIGURE 3 ) inner and outer plate similar in length and wide; inner plate with many simple setae and eleven serrate setae on apex, inner margin with two papposerrate setae (one slightly smaller); outer plate with several long simple and serrate setae on the apex.

Maxilliped ( Fig. 3J View FIGURE 3 ) plates with apex rounded; inner plate longer than width, with three cone shaped cuspidated setae on apex and small pappose setae at distal margin, inner margin with seven pappose setae and three small pappose setae in distal face, outer margin smooth; outer plate 1.2x longer than inner plate, with inner margin and apex covered by long simple setae and outer margin smooth; palp with four articles with several simple setae at distal and inner margin; Dactylus unguiform with some simple setae and distal nail present.

Gnathopod 1 ( Fig. 4A, 4A View FIGURE 4 1 View FIGURE 1 ) subchelate; base long with one simple seta on posterior margin; ischium and merus with group of simple setae on disto-posterior margin; carpus longer than wide and longer than propodus, posterior lobe long and convex, forming a shell-shaped structure with margin covered by serrate setae, inner face with seven to eight serrate setae with accessory setae, and disto-anterior margin with cluster of nine serrate setae; propodus length 1.3 times the maximum width, hammer-shaped, inner face with five serrate setae with accessory setae and seven to nine simple setae, disto-anterior margin with comb-scales and two simple setae, disto-posterior border covered by comb-scales and cluster of eight to ten simple setae; palm slightly transverse and covered by simple and smaller cuspidate setae with accessory seta, with three long and slender simple setae, disto-posterior border of palm with one cuspidate setae with accessory seta; dactylus claw-like and covered by comb-scales, length not exceeding the margin of the palm, with one small plumose setae in outer margin.

Gnathopod 2 ( Fig. 4B, B View FIGURE 4 1 View FIGURE 1 ) subchelate; base long with comb-scales and five group of two simple setae on margin; ischium and merus with comb-scales and long simple setae on disto-posterior margin; carpus with distal margin slightly quadrate, posterior lobe of carpus longer than wide, posterior margin with pectinate border with a row of serrate setae; propodus ovate, 1.3 times longer than wide, with one simple seta on anterior margin, length about 2.8 times of maximum length of posterior margin, with a cluster of simple setae on border, pronounced posterior lobe covered by comb-scales and three smaller simple setae and one cuspidate setae with accessory setae; palm slightly longer than posterior margin of propodus, with inclination transverse and convex, covered by simple and cuspidate setae of medium size; dactylus claw-like and smooth, not exceeding the palm margin in length, with one small plumose setae in outer margin.

Pereopods 3 and 4 ( Fig. 5A, 5B View FIGURE 5 ) similar in shape and size, coxal plates with margins covered by simple setae;pereopod 3 coxal plate longer than wide, pereopod 4 coxal plate excavated posteriorly and wider than coxa 3; both coxal plates with margins bordered with thin simple setae; anterior margin of merus, carpus and propodus with cluster of two or three distal setae; dactylus less than half length of propodus in both pereopods. Pereopods 5 and 6 ( Fig 5C–D View FIGURE 5 ) slightly shorter than pereopods 3 and 4, with similar shape and size with propodus, carpus, merus, ischium and base with several simple and cuspidate setae with accessory setae on anterior and posterior margins and dactylus less than half length of propodus. Pereopod 7 ( Fig. 5E View FIGURE 5 ) shorter than others, with propodus, carpus, merus, ischium and base with several simple and cuspidate setae with accessory setae on anterior and posterior margins and dactylus less than half the length of propodus.

Pleopods ( Fig. 6A View FIGURE 6 ) all similar, peduncle long and smooth with two coupling spines distally, ramus longer than peduncle, with several long plumose setae distributed on both margins.

Uropod 1 ( Fig. 6B View FIGURE 6 ) peduncle longer than wide, slightly longer than ramus, with six cuspidate setae with accessory seta on superior margin; outer ramus with four cuspidate setae with accessory setae distributed along the margin of the ramus, apex with four cuspidate setae (two cuspidate setae with accessory setae); inner ramus with three cuspidate setae with accessory setae on outer side of ramus, inner side with curved seta not reaching the apex of ramus, followed by six cuspidate setae with decreasing size lined up row and more three cuspidate setae.

Uropod 2 ( Fig. 6C View FIGURE 6 ) peduncle shorter than ramus, with four cuspidate setae with accessory seta; outer ramus with three cuspidate setae with accessory seta on margin and apex with four cuspidate setae (two cuspidate setae with accessory setae); inner ramus with three cuspidate setae with accessory seta and apex with six cuspidate setae (four cuspidate setae with accessory setae).

Uropod 3 ( Fig. 6D View FIGURE 6 ) peduncle longer than wide (rectangular), shorter than ramus with 9–10 cuspidate setae with accessory seta and one simple setae on the other side of the margin, and four simple setae more bellow; ramus slender with eight to ten simple setae apically and one cuspidate seta small and robust.

Telson ( Fig. 6E View FIGURE 6 ) as long as wide (square) with ten cuspidate setae with accessory setae and three short plumose setae at each side laterally more below.

Coxal gills sac-like present on pereonites 2 to 6.

Sternal gills tubular present on pereonites 2 to 7.

Description of female (paratypes). Mean body length: 5.85 ± 0.37 mm (n= 10), mean head length = 0.62 ± 0.04 mm (n=10). Antenna 1 ( Fig. 7A View FIGURE 7 ) peduncle formed by three articles; first article longer than wide and larger than the others article; flagellum composed of 10 articles, with groups of simple setae. Aesthetascs observed in articles four to ten. Antenna 2 ( Fig. 7B View FIGURE 7 ) not reaching half length of the body; peduncle formed by three articles, greater than length of head; flagellum with 12 articles, with groups of simple setae. Telson similar to male.

Gnathopod 1 ( Fig. 7C, 7C View FIGURE 7 1 View FIGURE 1 ) subchelate; long base, with one simple seta at posterior margin, disto-posterior margin with six simple setae; ischium without comb-scales on the posterior margin and five simple setae on the distal margin; merus with the disto-posterior margin ovoid, without comb-scales and six serrate setae; carpus longer than wider, posterior margin convex, forming a shell-like structure, covered by serrate setae arranged in a row on the margin, inner face of the carpus with four serrate setae with accessory setae, anterior margin smooth, distal margin with six serrate setae; propodus 1.5x longer than wider,, hammer-shaped, anterior margin with two serrate setae, disto-anterior and disto-posterior margin covered by comb-scales, disto-anterior margin with two simple setae, disto-posterior margin with a cluster of ten mall simple setae, inner face with five serrate setae with accessory setae arranged in row and three simple setae; outer face of propodus not observed; straight palm, covered by smaller cuspidate setae with accessory seta and simple setae of the medium-sized, and two simple setae long and slender, disto-posterior margin of the palm with two robust and short cuspidate seta with accessory seta; dactyl claw-like, not exceeding the length of the palm, covered by comb-scales with a small plumose seta on the posterior margin.

Gnathopod 2 ( Fig. 7D, 7D View FIGURE 7 1 View FIGURE 1 ) subchelate; long base without comb-scales and four setae on margin, disto-posterior margin with five simple setae; ischium without comb-scales on posterior and distal margin with five simple setae; merus without comb-scales on the posterior margin, distal margin ovoid with group of six serrate setae distributed; carpus longer than wide, posterior margin convex, forming shell-like structure, with serrate setae arranged in row on the distal margin, inner face with three serrate setae with accessory setae, disto-anterior margin with six long serrate setae; propodus rectangular, 1.6x longer than wider, anterior margin with long simple setae, posterior margin with three simple setae, disto-anterior and disto-posterior margin covered by comb-scales, inner face with three serrate setae with accessory seta; palm straight with margin of propodus covered by smaller cuspidate setae with accessory seta and simple setae of the medium-sized, disto-posterior margin of palm with two robust and short cuspidate seta with accessory seta; dactylus claw-like, shorter than palm, covered by comb-scales and with small plumose seta on posterior margin.

Etymology. The species name “ terrasolis ” refers to the location where this new species was found, Granja Terra do Sol, municipality of Palmeira das Missões, state of the Rio Grande do Sul, southerm Brazil.

Taxonomic remarks. The analyses were based on the data and morphological characteristics presented in recent articles describing new species for the genus Hyalella , published for the south of Brazil and Argentina ( Santos et al., 2008; Rodrigues et al., 2012; Streck-Marx & Castiglioni, 2020; Reis et al., 2020; Talhaferro et al., 2021a; Limberger et al., 2021; Penoni et al., 2021; Rangel et al., 2022; Limberger et al., 2022; Isa Miranda & Peralta, 2022; Reis et al., 2023; Limberger et al., 2024). Additionally, taxonomic keys provided by Rogers et al. (2020) and Talhaferro et al. (2021b) were used.

Comparative analyses highlight that H. terrasolis sp. nov. does not correspond to any of the species previously described within the genus, presenting a unique characteristic: an arrangement of six decreasingly sized cuspidate setae aligned in a row, followed by three additional cuspidate setae located between the curved seta and the apex of the inner ramus of uropod 1 ( Fig. 8A View FIGURE 8 ). Other noteworthy features include the unusually shaped lobe of the propodus of gnathopod 2, very pronounced ( Fig. 8B View FIGURE 8 ), and the presence of 10 cuspidate setae with accessory setae on the apical margin of the telson ( Fig. 6E View FIGURE 6 ).

Among the species recorded for state of the Rio Grande do Sul, H. jaboticabensis Limberger, Santos & Castiglioni, 2024 is the most similar to H. terrasolis sp. nov. The characteristics contributing to the resemblance include the presence of two papposerrate setae on the inner margin of maxilla 2, a similar number of articles in antennae 1 and 2, and the presence of serrate and simple setae on the inner face of the propodus of gnathopod 1 (although differing in the number of setae). Additionally, both species have a similar apical shape in the telson, but they differ in the number and arrangement of setae (Table 1).

In addition to the previously mentioned characteristics, H. terrasolis sp. nov. shows two paposserrated setae on the inner margin of maxilla 2. In comparison to the species found in the state of Rio Grande do Sul, this characteristic is shared with H. lagoana Talhaferro & Bueno, 2021 , H. minuana Talhaferro & Bueno, 2021 , H. kaingang Araujo & Cardoso, 2013 , H. jaboticabensis , H. imbya Rodrigues & Bueno, 2012 , H. gauchensis Streck & Castiglioni, 2017 , H. georginae Streck & Castiglioni, 2017 , and H. longipropodus Limberger, Graichen & Castiglioni, 2021 (Table 1).

The presence of a curved seta on the inner ramus of uropod 1 is a common characteristic found in most species recorded for the state of Rio Grande do Sul, except for H. pseudoazteca Gonzalez & Watling, 2003 and H. longipropodus . Hyalella terrasolis sp. nov. shares this characteristic with other species in the region. However, in addition to the mentioned features, H. pseudoazteca and H. longipropodus do not exhibit any other morphological similarities with H. terrasolis sp. nov. (Table 1).

Hyalella terrasolis sp. nov. features five serrate setae with an accessory seta on the inner face of the propodus and carpus of gnathopod 1 ( Fig. 8C, D View FIGURE 8 ). This type of setae was recently described by Reis et al. (2023) and has been observed only in H. carsone Reis, Bueno & Araujo, 2023 and H. wangarie Reis, Bueno & Araujo, 2023 so far in the state of Santa Catarina, being a characteristic shared with H. terrasolis . However, there are no records of this characteristic in other species occurring in the state of Rio Grande do Sul.

About the number of serrated setae on the inner face of the propodus of gnathopod 1, H. terrasolis sp. nov. resembles H. curvispina Shoemaker, 1942 , H. pampeana Cavalieri, 1968 , H. gauchensis , H. palmeirensis Streck-Marx & Castiglioni, 2020 and H. bonariensis Bond-Buckup, Araujo & Santos, 2008 (Table 1). However, H. terrasolis sp. nov. additionally shows seven to nine small simple setae that is not evident in any of these other species. Furthermore, H. terrasolis sp. nov. differs from these and other species in the number of cuspidate setae found on the peduncle of uropod 3, exhibiting nine or 10 setae, a characteristic shared only with H. gauchensis , which has nine cuspidate setae. However, H. gauchensis does not show evident similarities in the ramus of uropod 3, as well as in the shape, number of setae, and setation pattern of the telson when compared to H. terrasolis sp. nov.

The apical shape of the telson, presenting a square appearance in H. terrasolis sp. nov., is similar to the shape found only in H. jaboticabensis and H. palmeirensis , whereas other species exhibit a rounded or pointed shape. However, the telson of Hyalella terrasolis sp. nov. differs by having 10 cuspidate setae with accessory setae on its apical margin, while H. jaboticabensis has six to eigth setae with the same characteristic, and H. palmeirensis has only two simple setae, without the presence of accessory setae. The number and setation pattern found in H. terrasolis are not evident in any other species recorded for the region, where the species with the closest resemblance in the number of setae on the telson is H. montenegrinae Bond-Buckup & Araujo, 1998 , which can have up to nine cuspidate setae. However, besides the presence of external gills between segments 2–7, this is the only close similarity between H. terrasolis and H. montenegrinae .