Hyalella sumida Penoni and Bueno, 2025

Hyalella sumida Penoni and Bueno sp. n.

( Figures 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 )

Type material

Holotype male ( Figure 2A View Figure 2 ), body length = 7.25 mm, head length = 0.6 mm, ‘ Gruta da Água Sumida’ Cave , Parque Estadual Turístico do Alto Ribeira , Iporanga municipality, São Paulo state, Brazil (24.47833°S, 48.62889°W), MNRJcarcino 31359 , July 2018, Bichuette, M.E., Zepon, T. coll GoogleMaps ; allotype female ( Figure 2B View Figure 2 ), body length = 3.87 mm, head length = 0.4 mm, ‘ Gruta da Água Sumida’ Cave , Parque Estadual Turístico do Alto Ribeira , Iporanga municipality, São Paulo state, Brazil (24.47833ºS, 48.62889°W), MNRJcarcino 31360 , July 2017, Bichuette, M.E., Zepon, T., coll. GoogleMaps ; paratype one male, CCUFLA 455 , November 2009, Bichuette, M.E., Zepon, T., two males, LES0018586 About LES and LES0018591 About LES , same collection site as holotype, April 2018, Bichuette, M.E., Zepon, T. coll. (same collection data as holotype), GoogleMaps two males on slides CCUFLA 456 (same collection data as holotype). GoogleMaps

Diagnosis

Body surface smooth. Epimeron 2 postero-distal margin acute. Antennae 1 and 2 shorter than half the body length. Maxilla 1 palp longer than half the distance between the base of the palp and the base of setae on the outer plate; outer plate with 9 serrate setae. Gnathopod 2 propodus ovate, palm subequal to posterior margin of propodus and with a minute posterior excavation, slope oblique. Uropod 1 of the male without a curved seta on inner ramus. Uropod 3 longer than the telson, peduncle and ramus subequal. Coxal gills on segments 2–6. Sternal gills on segments 2–7.

Male

Mean body length 8.93 ± 2.2 mm (N = 3) (7.25–11.45 mm); mean head length 0.9 ± 0.25 mm (N = 3) (0.6–0.87 mm). Body surface smooth. Epimeral plates 2 accuminated ( Figure 3I View Figure 3 ). Coxae 1–3 similar ( Figure 4A–C View Figure 4 ), subequal in size; coxa 4 as wide as long, excavated posteriorly ( Figure 4D View Figure 4 ); coxae 5–7 with some scattered microtrichs (very small, not represented in the drawings). Eyes present.

Antenna 1 ( Figure 3A View Figure 3 ) shorter than half the body length (0.3× the body length), 0.8× the length of antenna 2, 1.6× longer than the peduncle of antenna 2 and 1.5× longer than the flagellum of antenna 2. Peduncle articles 1–3 relative length 1:0.82:0.63; flagellum with 17–18 articles; aesthetascs occurring distally on flagellum starting at article 5 until the last one.

Antenna 2 ( Figure 3B View Figure 3 ) not reaching half the body length (0.4× the body length); peduncle slender, almost 4× the length of the head; flagellum with 15 articles, 1.1× longer than the peduncle.

Mandible without palp; incisor toothed; left ( Figure 3C View Figure 3 ) lacinia mobilis with 5 teeth, setae row with 4 pappose setae, an accessory seta on the molar process; right mandible ( Figure 3D View Figure 3 ) with 2 pappose setae and some setules; molar process cylindrical with an accessory seta.

Upper lip ( Figure 3E View Figure 3 ) margin rounded; distal border covered by setules. Lower lip ( Figure 3F View Figure 3 ) outer lobes rounded, distally notched, covered by setules apically.

Maxilla 1 ( Figure 3G View Figure 3 ) inner plate slender, with 2 apical pappose setae and lateral setules. Outer plate with 9 serrate setae, and a few setules on the inner margin, apically. Palp relatively long, uniarticulate, longer than wide, reaching more than half the distance between the base of the palp and base of the setae on the outer plate, with 1 simple seta.

Maxilla 2 ( Figure 3H View Figure 3 ) inner plate shorter than outer plate, inner plate with 2 strong pappose setae distally and some simple and pappose setae disto-apically, and setules laterally; outer plate with long simple setae and some serrate setae, disto-apically, and setules laterally.

Maxilliped ( Figure 3J View Figure 3 ) without comb scales; inner plate with 3 cuspidate distal setae apically, a few pappose setae disto-apically; outer plate with several long simple setae on the inner margin and 2 smaller simple setae on the outer margin; palp longer than inner and outer plates, with 4 articles; article 1 inner margin with up to 4 long simple setae and outer margin with 3 simple setae; article 2 inner margin with several long simple setae and outer margin with 4 long simple setae; article 3 distal inner and outer margins with several long and thin simple setae; article 4 (dactylus) unguiform with distal nail present, with up to 5 simple setae, shorter than nail.

Gnathopod 1 ( Figure 4A View Figure 4 ) subchelate; coxal plate 1.7× wider than long, with simple setae on the margin and up to 3 serrate setae on the posterior inner face, close to the attachment of the basis; basis with 5 serrate setae on the posterior margin, 1 small simple setae on the disto-anterior margin and 2 serrate setae on the disto-posterior margin; ischium with 1 serrate seta and 1 simple seta postero-apically; merus with 7 serrate setae and 1 pappose seta posteriorly; carpus longer than wide, with pappose setae on the lateral distal lobe, 5 pappose setae on inner margin, up to 9 serrate setae antero-distally, and 2 serrate setae on the anterior margin; propodus 1.5× longer than wide, hammer shaped, up to 10 long simple setae on disto-posterior margin, comb-scales on the disto-posterior corner, numerous long and short simple setae on disto-anterior margin; palm slope transverse, with several long and short simple setae; up to 10 pappose setae and 1 cuspidate seta with accessory seta on inner face; dactylus claw-like, with polygonal pattern and a plumose seta distally.

Gnathopod 2 ( Figure 4B View Figure 4 ) subchelate, without comb scales; coxal plate 1.9× wider than long, with simple setae on the margin; basis with 6 long serrate setae on posterior margin, 1 short simple seta on anterior margin, and up to 2 serrate setae disto-posteriorly; ischium with 3 serrate setae disto-posteriorly; merus with 9 serrate setae, divided into 2 groups, disto-posteriorly; carpus lobe slim, produced between merus and propodus, posterior margin with pappose setae, disto-anterior margin with 5 serrate setae; propodus ovate, posterior margin 1.3× longer than the palm, slope oblique, posterior margin with several short simple setae, disto-posterior corner with polygonal pattern, palm posteriorly excavated, some short cuspidate setae with accessory setae and some simple setae, anterior margin with a few simple setae; dactylus claw-like, congruent with palm and with 1 plumose seta distally.

Pereopods 3–7 ( Figure 4C–G View Figure 4 ) simple. Simple setae distally on all coxae, and a few microtrichs on inner face of coxae 5–7; coxa 3 similar to 1 and 2; coxa 4 as long as wide, excavated posteriorly; coxa 5 posterior lobe longer than anterior lobe; coxa 6 anterior lobe reduced; coxa 7 reduced. Pereopods 3–5 subequal in size, pereopod 6 1.3× longer than P3–5 and slightly longer than P7. Pereopods 3 and 4 basis with 2 to 3 groups of 1 or 2 serrate setae on the posterior margin, 2 to 3 serrate setae on the disto-posterior margins of basis and ischium, 3 to 5 groups of 1 to 3 simple setae on the posterior margin of the merus, 4 to 7 groups of simple and/or cuspidate setae with accessory setae on the posterior margins of carpus and propodus; pereopod 3 merus with 2 cuspidate setae with accessory seta on the anterior margin. Pereopods 5–7 with small simple setae on the posterior margin of the basis, 2 or 3 serrate setae postero-apically, 7 to 9 groups of 1 to 2 cuspidate setae with or without accessory seta on the anterior margins of the basis, and up to 5 cuspidate setae with accessory seta on the disto-anterior margin; merus posterior margins with 2 curved cuspidate setae with accessory seta; merus, carpus and propodus anterior margins with 2 to 5 groups of cuspidate setae with or without accessory seta and simple setae, disto-anterior and disto-posterior margins with up to 9 cuspidate setae with accessory seta. Pereopods 3–7 dactylus with a plumose seta.

Pleopods ( Figure 5A View Figure 5 ) peduncle half the length of the rami, no coupling spines observed, both rami with several long plumose setae.

Uropod 1 ( Figure 5B View Figure 5 ) peduncle 1.3× longer than inner ramus and 1.5× longer than the outer ramus, with up to 6 cuspidate setae with accessory seta; inner ramus 1.2× longer than the outer ramus, with 3 cuspidate setae with accessory seta on dorsal margin and 5 cuspidate setae (3 longer, 2 shorter) apically; outer ramus with 3 cuspidate setae on dorsal margin and 4 cuspidate setae (2 longer, 2 shorter) apically.

Uropod 2 ( Figure 5C View Figure 5 ) less than 0.7× the total length of uropod 1, 1.2× longer than the peduncle of uropod 1, peduncle subequal to inner ramus, 1.2× longer than the outer ramus, with 3 cuspidate setae; inner ramus 1.2× longer than outer ramus, with 2 cuspidate setae with accessory seta on dorsal margin and 4 cuspidate setae (2 longer, 2 shorter) apically; outer ramus with 3 cuspidate setae with accessory seta on dorsal margin and 4 cuspidate setae (2 longer, 2 shorter) apically.

Uropod 3 ( Figure 5D View Figure 5 ) half the length of the peduncle of uropod 1 and 0.9× the length of the peduncle of uropod 2, 1.2× longer than the telson; peduncle with 4 cuspidate setae on inner distal margin; inner ramus absent; outer ramus with a small dentation midway bearing 1 cuspidate seta with accessory seta, and 5 cuspidate setae with an accessory seta and a triangular cuspidate seta apically.

Telson ( Figure 5E View Figure 5 ) entire, as long as wide, apically rounded with 2 simple setae; 2 small plumose setae on each side, symmetrically.

Epimeron ( Figure 3I View Figure 3 ) 1 and 3 postero-distal margin sub-acute, epimeron 2 postero-distal margin acute; first epimeron shorter than the second and third.

Coxal gills sac-like on pereonites 2–6. Sternal gills tubular on pereonites 2–7.

Female

( Figure 2B View Figure 2 ). Allotype female not dissected. Body length = 3.87 mm; head length = 0.4 mm.

Etymology

The species epithet sumida is a reference to the cave where this species occurs, Gruta da Água Sumida.

Habitat

Freshwater, hypogean, troglophilic species (organisms able to live their entire life in a cave). A few specimens of Hyalella sumida sp. n. were found in the water pools of Gruta da Água Sumida Cave, showing low abundance.

Conservation

Hyalella sumida sp. n. is classified as endangered (EN) based on the International Union for Conservation of Nature (IUCN) subcategory B1 (<5000 km 2 area of occurrence) and D1 (<250 mature individuals) (ICMBIO 2013).

Remarks

Hyalella sumida sp. n. is a troglophilic species, with no apparent specialisations to subterranean life. One unusual characteristic is the presence of setae on the anterior margin of the carpus of gnathopod 1 (besides the ones present at the disto-anterior margin), which differentiate it from almost all of the known species of the genus. Considering the Brazilian species, H. sumida sp. n. is different from 21 described species of Hyalella by the absence of a curved seta on the inner ramus of the male uropod 1. There are 19 other species (described and/or under description) that lack this seta. We can distinguish H. sumida sp. n. from H. caeca Pereira, 1989 and H. troglofugia Bastos-Pereira, Oliveira and Ferreira, 2018 , because these are species that lack eyes and have the maxilla 1 palp short. The relative size of the palp can be used to differentiate the new species from all but one ( H. temimina ) of these 19 species. One important difference between the new species and H. temimina is the comb scale and polygonal pattern presence and distribution at the gnathopods. And the new species has an antenna 2 shorter than half the body length, which is different from H. spelaea Bueno and Cardoso, 2011 ( Cardoso et al. 2011), H. gracilicornis (Faxon, 1876) ( González and Watling 2003) , H. longiprodus Limberger, Graichen and Castiglioni, 2021 ( Limberger et al. 2021), H. longistila (Faxon, 1876) ( González and Watling 2003) and H. warmingi Stebbing, 1899 ( González and Watling 2003) which have antenna 2 longer than half the body length, and from H. virgineae which has antenna 2 as long as half the body length.