Hyalella terrasolis Limberger, Castiglioni & Santos, 2025, sp. nov.

Hyalella terrasolis sp. nov. Castiglioni, Limberger & Santos Figures 1–8 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). 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). Type specimens. Holotype: male, body length = 7.93 mm; head length = 0.84 mm (Fig. 2A) (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), May 21, Limberger, M. & Castiglioni, D.S. cols. Allotype: female, body length = 5.86 mm, head length = 0.62 mm (Fig. 2B) (MNRJcarcino 31354), same date and locality of the holotype. Paratypes: (MNRJcarcino 31355), 20 whole specimens (10 males and 10 females); (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). 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 1). Antenna 1 (Fig. 3B) 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) 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) incisor process with five teeth and two pappose setae with group of setules. Left mandible (Fig. 3E) 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) with rounded borders and presence of several simple setae and setules; ventral margin with many setules. Lower lip (Fig. 3G) bilobed, with distal margins ovoid with many simple setae and setules on inner and distal margins, outer margin smooth. Maxilla 1 (Fig. 3H) 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) 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) 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 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 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) 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) 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) 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) 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) 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) 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) 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) 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) 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 article