Hyalella karaja, Cardoso & Oliveira & Ferreira, 2025

Hyalella karaja sp. nov.

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Figures 1 View FIGURE 1 , 2D View FIGURE 2 , 6–8 View FIGURE 6 View FIGURE 7 View FIGURE 8 , 15B, C View FIGURE 15

Type material: Brazil, Pará state, Canaã dos Carajás municipality: Holotype ♂ (ISLA97012), S11C_0183 cave (-6.4099º -50.3969º), 09.IV.2016, leg. M. P. Oliveira. Paratypes: 2♂, 5♀ ( ISLA 44356, part in slide), same data as holotype; 1♂, 1♀ ( ISLA 105435), S11C_0103 cave (-6,4049º -50,3883º), 11.II.2023, leg. M. P. Oliveira.

Diagnosis: Eyes absent or reduced; antenna 1 shorter than antenna 2; flagellum of six articles; flagellum of antenna 2 with eight articles; propodus of gnathopod 1 ventral face with two serrate setae; propodus of gnathopod 2 ovate, palm longer than posterior margin with small lobe with comb scales, slope oblique; telson two cuspidate setae with accessory seta apically, plus three small setae laterally.

Description

Male: Body length of 2.8 mm; cephalothorax length of 0.15 mm. Body surface smooth. Epimeral plates not acuminate. Cephalothorax slightly longer than first thoracic segment, rostrum absent. Eyes absent ( Figs 2D View FIGURE 2 , 15B,C View FIGURE 15 ). Antenna 1 ( Fig. 6A View FIGURE 6 ) shorter than antenna 2; flagellum of six articles, longer than peduncle. Antenna 2 ( Fig. 6B View FIGURE 6 ) less than half body length, peduncle longer than cephalothorax, flagellum with eight articles, longer than peduncle. Mandible ( Fig. 6C,D View FIGURE 6 ) incisor with five to six teeth; lacinia mobilis denticulated; left mandible setal row with three pappose setae; right mandible with two pappose setae; molar large, cylindrical, and triturative; accessory seta present. Upper-lip margin rounded, and distal margin covered by setules on ventral and dorsal faces. Lower-lip ( Fig. 6E View FIGURE 6 ) bilobed, outer lobes rounded with several setules on ventral and dorsal faces, outer margin smooth. Maxilla 1 ( Fig. 6F View FIGURE 6 ) palp short, uniarticulate, longer than wide, with one strong seta; inner plate slender, smaller than outer plate, with two strong pappose apical setae; outer plate with eight serrate setae. Maxilla 2 ( Fig. 6G View FIGURE 6 ) inner plate shorter than outer plate, with two strong papposerrate setae, and several serrate setae; outer plate with simple setae. Maxilliped ( Fig. 6H View FIGURE 6 ) inner plates apically rounded, with three cuspidate and pappose setae apically, medially and on outer margin; outer plate as wide as inner plate, apically rounded with apical and medial simple setae; palp longer than outer plate, with four articles, with simple setae; dactylus unguiform, shorter than article 3; distal setae simple, inner margin with setae, distal nail present.

Gnathopod 1 ( Fig. 6I View FIGURE 6 ) subchelate; dactylus claw-like, distal margin with one plumose seta; propodus length less than two times maximum width, hammer shaped, ventral face with two serrate setae and some small simple and cuspidate setae, dorsal face with simple setae, anterodistal margin with some comb scales and cluster of simple setae, posterodistal margin with strong cuspidate setae with accessory seta, and comb scales; carpus longer than wide, longer and wider than propodus, with strong and wide posterior lobe with pectinate border and row of serrate setae; base, ischium and merus with few simple setae on posterodistal margin.

Gnathopod 2 ( Fig. 6J View FIGURE 6 ) subchelate; dactylus claw-like, long, longer than half of propodus length; propodus ovate, length about 1.5 maximum width, palm longer than posterior margin, slope oblique, with several cuspidate setae with accessory seta and simple setae, small lobe with comb scales; carpus wider than long with posterior lobe elongated produced between propodus and merus, border pectinate with several pappose setae; base, ischium and merus with simple setae on posterior margin, and posterodistal margin.

Pereopods 3 and 5 ( Fig. 7A–C View FIGURE 7 ) similar in size; pereopod 4 slightly longer; with propodus, carpus, merus, ischium, and base with several simple and cuspidate setae with accessory seta on posterior and anterior margin; dactylus less than half the length of propodus. Pereopod 6 ( Fig. 7D View FIGURE 7 ) longer than others, with pereopod 7 ( Fig. 7E View FIGURE 7 ) slightly shorter. Coxal plate of pereopod 4 excavated posteriorly; trapezoidal shaped on pereopod 5, oval shaped on pereopod 6 and reduced on pereopod 7.

Pleopods ( Fig. 7F View FIGURE 7 ) not modified; peduncle slender, shorter than rami, with two coupling spines distally; rami with several plumose setae on both margins.

Uropod 1 ( Fig. 8A View FIGURE 8 ) longer than uropod 2; peduncle longer than rami, with one dorsal cuspidate seta with accessory seta; inner ramus with one dorsal cuspidate seta with accessory seta, four cuspidate setae apically; outer ramus with two dorsal cuspidate setae and four cuspidate setae apically. Uropod 2 ( Fig. 8B View FIGURE 8 ) peduncle slightly longer than rami, with two dorsal setae; inner ramus longer than outer ramus, with one dorsal cuspidate seta and four cuspidate setae apically; outer ramus two five dorsal cuspidate setae and four distal setae. Uropod 3 ( Fig. 8C View FIGURE 8 ) shorter than other uropods; peduncle slightly longer than wide, with three distal cuspidate setae; inner ramus absent; outer ramus uniarticulate, with three simple setae apically.

Telson ( Fig. 8D View FIGURE 8 ) as long as wide, entire, apically rounded, bearing two cuspidate setae with accessory seta apically, plus three small setae laterally.

Coxal gills sac-like, present on gnathopod 2 to pereopod 6. Sternal gills tubular, present on segments 2 to 7.

Female ( Fig. 8E–J View FIGURE 8 ): body length of 3.3 mm; cephalothorax length of 0.3 mm. Eyes reduced.Antenna 1 flagellum of five articles. Antenna 2 flagellum of seven articles. Gnathopod 1 ( Fig. 8E View FIGURE 8 ) similar in size and shape to male gnathopod 1; propodus inner face with three serrate setae, anterodistal and posterodistal with comb scales; carpus posterior lobe with pectinate border and row of serrate setae. Gnathopod 2 ( Fig. 8F View FIGURE 8 ) propodus rectangular, more elongated than gnathopod 1, with length about two times width, subchelate; propodus anterodistal and posterodistal margin with simple setae; carpus posterior lobe with pectinate border with row of serrate setae. Uropod 1 and 3 ( Fig. 8G,I View FIGURE 8 ) similar to male. Uropod 2 ( Fig. 8H View FIGURE 8 ) peduncle slightly longer than rami, with three dorsal setae; inner ramus longer than outer ramus, with two dorsal cuspidate setae and four cuspidate setae apically; outer ramus two dorsal cuspidate setae and four distal setae. Telson ( Fig. 8J View FIGURE 8 ) bearing three cuspidate setae with accessory seta apically, plus three small setae laterally.

Etymology: The species name, karaja, refers to the indigenous tribe that inhabits the region that bears the same name, Serra de Carajás (Carajás Mountain Range).

Morphological remarks: In Hyalella karaja sp. nov. some specimens presented reduced eyes, while in others, eyes were absent, this variation was noticed in the troglobite species H. veredae (Zeppon et al. 2021) and in the epigean species H. montana Rodrigues, Senna, Quadra & Bueno, 2017 . This variation in the eyes may reflect the degree and duration of isolation experienced by each population in subterranean environments (Zeppon et al. 2021).

Hyalella karaja sp. nov. differs from H. amazonica sp. nov. by the reduced number of articles on the antennae (antenna 1 with 6 and antenna 2 with 8 versus antenna 1 with 14 and antenna 2 with 11 in H. amazonica sp. nov.), and length of the antennae with antenna 1 shorter than antenna 2 versus antenna 1 and antenna 2 with similar length in Hyalella amazonica sp. nov., and the setae on telson, with two cuspidate setae versus two simple and two cuspidate setae on in Hyalella amazonica sp. nov.

Hyalella spelaea also presents reduced eyes, however, it differs from Hyalella karaja sp. nov. by the number of articles on antennae, H. spelaea presenting antenna 1 with 9 articles and antenna 2 with 16, the type of setae on telson (simple on H. spelaea , and cuspidate on Hyalella karaja sp. nov.).