Hyalella amazonica, Cardoso & Oliveira & Ferreira, 2025

Hyalella amazonica sp. nov.

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Figures 1 View FIGURE 1 , 2C View FIGURE 2 , 3–5 View FIGURE 3 View FIGURE 4 View FIGURE 5 , 15A View FIGURE 15

Type material: Brazil, Pará state, Canaã dos Carajás municipality: Holotype ♂ (ISLA66169), ST_0042 cave (- 6.3133º -50.093º), 14.VII.2016, leg. M. P. Oliveira. Paratypes: 1♂, 3♀ ( ISLA 66172, 2 in slide), same data as holotype ; 4♀ ( ISLA 66171), same location as holotype, 01.II.2016 ; 2♂, 1♀ ( ISLA 66168), ST_0041 cave (-6.3134º -50.0926º), 23.I.2016 ; ST_0041 cave, 23.I.2016; 2♂ ( ISLA 66170, 1 in slide), ST_0041 cave, 19.VII.2016 .

Diagnosis: Eyes absent; antenna 1 as long as antenna 2 with 14 articles on flagellum; antenna 2 flagellum with 11 articles; propodus of gnathopod 1 ventral face with three serrate setae; telson with two medial simple setae and two cuspidate setae with accessory seta.

Description

Male: Body length of 3.8 mm; cephalothorax length 0.37 mm. Body surface smooth. Epimeral plates not acuminate. Cephalothorax slightly longer than first thoracic segment, rostrum absent. Eyes absent ( Figs 2C View FIGURE 2 , 15A View FIGURE 15 ). Antenna 1 ( Fig. 3A View FIGURE 3 ) as long as antenna 2; flagellum of 14 articles, longer than peduncle. Antenna 2 ( Fig. 3B View FIGURE 3 ) less than half body length, peduncle longer than cephalothorax, flagellum with 11 articles, longer than peduncle. Mandible incisor with six teeth; lacinia mobilis with six teeth; left mandible ( Fig. 3C View FIGURE 3 ) setal row with three long and robust pappose setae; right mandible ( Fig. 3D View FIGURE 3 ) with two pappose setae; molar large, cylindrical, and triturative; accessory seta present. Upper-lip ( Fig. 3E View FIGURE 3 ) margin rounded, and distal margin covered by short several setules on ventral and dorsal faces. Lower-lip ( Fig. 3F View FIGURE 3 ) bilobed, outer lobes rounded with several setules on ventral and dorsal faces, outer margin smooth. Maxilla 1 ( Fig. 3G View FIGURE 3 ) palp short, uniarticulate, longer than wide, with one strong seta; inner plate slender, smaller than outer plate, with two strong pappose apical setae and several simple setae on inner and outer margin; outer plate with nine serrate setae. Maxilla 2 ( Fig. 3H View FIGURE 3 ) inner plate shorter than outer plate, with two strong papposerrate setae, medial margin with one long seta and several simple and serrate setae on anterior margin; outer and inner plate with abundant simple setae. Maxilliped ( Fig. 3I View FIGURE 3 ) inner plate apically rounded, with three cuspidate setae, 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, without comb scales; distal setae simple, shorter than nail, inner margin with setae; distal nail present.

Gnathopod 1 ( Fig. 3J View FIGURE 3 ) subchelate; dactylus claw-like with one plumose seta; propodus length less than two times maximum width, hammer shaped, ventral face with three serrate setae, anterodistal margin one clusters of simple setae, posterodistal margin with one strong cuspidate seta with accessory seta, and comb scales; carpus longer than wide, longer and wider than propodus, strong and wide posterior lobe with pectinate border with several serrate setae; base, ischium and merus with few simple setae on posterodistal margin.

Gnathopod 2 ( Fig. 3K View FIGURE 3 ) subchelate; dactylus claw-like, short, 1/3 of propodus length, with one plumose seta, with comb scales; propodus ovate, length about 1.6 maximum width, with one cluster of simple setae distally, palm short, haft of posterior margin, slope oblique, with row of cuspidate setae with accessory seta and simple setae; carpus wider than long with posterior lobe elongated between propodus and merus, border pectinate with several pappose setae; base, ischium and merus with few simple setae on posterior margin.

Pereopods 3 and 5 ( Fig. 4A–C View FIGURE 4 ) similar in size; pereopod 4 slightly longer, pereopod 5 shortest; 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. 4D View FIGURE 4 ) longer than others, pereopod 7 ( Fig. 4E View FIGURE 4 ) slightly shorter than pereopod 6.

Coxal plate of pereopod 4 excavated posteriorly, reduced on pereopods 5–7.

Pleopods ( Fig. 4F View FIGURE 4 ) not modified; peduncle slender, shorter than rami, with two coupling spines; rami with several plumose setae on both margins.

Uropod 1 ( Fig. 4G View FIGURE 4 ) longer than uropod 2; peduncle longer than rami, with five cuspidate setae with accessory seta; inner ramus with one dorsal cuspidate seta and three cuspidate setae apically; outer ramus with two dorsal cuspidate setae and three cuspidate setae apically. Uropod 2 ( Fig. 4H View FIGURE 4 ) peduncle shorter than rami, with three dorsal setae; rami subequal in length; inner ramus with one dorsal cuspidate seta and three cuspidate setae apically, outer ramus with two dorsal cuspidate setae and four apical setae. Uropod 3 ( Fig. 4I View FIGURE 4 ) shorter than other uropods; peduncle slender (rectangular), wider than ramus, with one cuspidate seta; inner ramus absent; outer ramus uniarticulate with two cuspidate setae and one long simple seta apically.

Telson ( Fig. 4J View FIGURE 4 ) as long as wide, entire, apically rounded with two medial simple setae and two cuspidate setae with accessory seta, distributed on distal margin, and three small plumose setae laterally.

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

Female ( Fig. 5 View FIGURE 5 ): body length of 3.6 mm; cephalothorax length: 0.23 mm. Antenna 1 flagellum of 11 articles. Antenna 2 flagellum of eight articles. Gnathopod 1 ( Fig. 5A View FIGURE 5 ) similar in size and shape of male gnathopod 1; ventral face with three serrate setae, anterodistally and posterodistally with comb scales; carpus posterior lobe with pectinate border with row of several serrate setae. Gnathopod 2 ( Fig. 5B View FIGURE 5 ) propodus rectangular, similar to gnathopod 1; propodus inner face with two serrate setae. Uropod 1 ( Fig. 5C View FIGURE 5 ) longer than uropod 2; peduncle shorter than rami, with four cuspidate setae with accessory seta; inner ramus with one dorsal cuspidate seta and three cuspidate setae apically; outer ramus with two dorsal cuspidate setae and three cuspidate setae apically. Uropod 2 ( Fig. 5D View FIGURE 5 ) peduncle shorter than rami, with three dorsal setae; rami subequal in length; inner ramus with one dorsal cuspidate seta and three cuspidate setae apically, outer ramus with two dorsal cuspidate setae and four apical setae. Uropod 3 and telson similar to male.

Etymology: The epithet is given in designation to the Amazon forest. All specimens were collected in the state of Pará, located in the Amazon rainforest.

Morphological remarks: Hyalella amazonica sp. nov. is a stygobite species from caves in the Amazon region. Hyalella amazonica sp. nov. differs from the other species by the absence of eyes, by the length of the antennae 1 and 2, by the shape of male gnathopod and by the number and type of setae on telson. Comparing with the other stygobite Hyalella species from Brazil, Hyalella amazonica sp. nov. resembles H. caeca and H. spelaea by the absence of a curved seta on uropod 1, however differs from them by the setae on telson, two simple setae on the middle plus one cuspidate on each side, while both H. caeca and H. spelaea have only two simple apical setae ( Pereira 1989; Cardoso et al. 2011). By the similar length of the antennae 1 and 2, Hyalella amazonica sp. nov. resembles H. veredae , however, H. veredae presents a curved seta on uropod 1 ( Cardoso et al. 2014).