Hyalella caeca Pereira 1989
Creators: name: Penoni, Ludmila Rocha
name: Bichuette, Maria Elina
name: Borges, Rayssa Karolina Ferreira
name: Bueno, Alessandra Angélica de Pádua
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Amphipoda
Hyalellidae
Hyalella
Hyalella caeca

description: Hyalella caeca Pereira, 1989
(Figures 12–15)
Type material
Paratype male (Figure 12 (A)), body length = 5.79 mm, head length = 0.50 mm, Gruta Tobias de Baixo Cave, Parque Estadual Turístico do Alto Ribeira, Iporanga municipality, São Paulo state, Brazil (24.5569°S, 48.7236°W), MNRJcarcino 7618, 6 November 1975, Guy Christian Collet coll.; paratype female (Figure 12 (B)), body length = 4.92 mm, head length = 0.44 mm, MNRJcarcino 7618; paratype male on slides (same collection data as holotype).
Material examined
Only material from the type locality.
Diagnosis
Maxilla 1 outer plate with 9 serrate setae. Male gnathopod 1 propodus 1.6× longer than wide, hammer shaped, inner face with a row of 6 papposerrate setae, with polygonal pattern on the dactylus. Gnathopod 2 propodus almost triangular, palm with a slender excavation posteriorly. Uropod 1 of the male without a curved seta on inner ramus. Telson almost square, 2 setae apically, 3 small plumose setae on each side, symmetrically placed. Coxal gills on segments 2–6. Sternal gills on segments 2–7.
Description
Male. Mean body length 5.79 ± 0.86 mm (N = 2) (5.79–7.00 mm); mean head length 0.5 ± 0.06 mm (N = 2) (0.5–0.59 mm). Body surface smooth. Epimeral plate 2 accuminated (Figure 13 (I)). Coxae 1–3 similar, subequal in size; coxa 7 reduced. Eyes absent.
Epimeron (Figure 13 (I)) 1, 2 and 3 postero-distal margins rounded, acute and sub-acute, respectively.
Antenna 1 (Figure 13 (A)) short, only 0.3× the body length and 0.7× the length of antenna 2, 1.8× longer than the peduncle of antenna 2 and slightly (1.1×) longer than the flagellum of antenna 2. Peduncle articles 1–3 relative length 0.9:1:0.7; flagellum with 10–11 articles; aesthetascs occurring distally on flagellum after article 4.
Antenna 2 (Figure 13 (B)) almost (0.88×) half the body length; peduncle slender, double the length of the head; flagellum with 13–14 articles, 1.4× longer than the peduncle.
Mandible without palp; incisor toothed; left (Figure 13 (C)) lacinia mobilis with 5 teeth, setae row with 3 pappose setae and a few setules, no observed accessory seta on the molar process; right mandible (Figure 13 (D)) with 2 pappose setae and some setules; molar process cylindrical with no observed accessory seta.
Upper lip (Figure 13 (E)) margin rounded; distal border covered by setules. Lower lip (Figure 12 (F)) outer lobes rounded, distally notched, covered by setules apically.
Maxilla 1 (Figure 13 (G)) inner plate slender, with 2 apical pappose setae and a few lateral setules. Outer plate with 9 serrate setae, and a few setules on the inner margin, apically. Palp short, uniarticulate, longer than wide, reaching less than half the distance between base of the palp and base of the setae on the outer plate, with 1 short strong simple seta distally.
Maxilla 2 (Figure 13 (H)) inner plate shorter than outer plate, inner plate with 1 strong pappose seta distally and some simple and serrate setae disto-apically; outer plate with longer simple setae and some papposerrate setae, disto-apically.
Maxilliped (Figure 13 (J)) without comb scales; inner plate with 3 cuspidate distal setae apically, a few pappose setae disto-apically and on the ventral margin, 2 simple setae on the outer margin; outer plate with several simple setae on the inner margin, 2 setae on the inner face 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 1 simple seta; article 2 inner margin with several long simple setae and outer margin with 3 simple setae; article 3 inner, distal and outer margins with several simple setae; article 4 unguiform with long distal papposerrate nail present, with up to 5 simple setae, shorter than nail.
Gnathopod 1 (Figure 14 (A)) subchelate; coxal plate 1.5× wider than long, with simple setae on the margin; basis posterior margin with 2 long bifid setae, disto-posterior margins with a group of 4 bifid setae; ischium with 1 disto-posterior simple seta; merus with 3 simple setae over the external margin, and up to 4 bifid setae disto-posteriorly; carpus longer than wide, with pappose setae on the lateral distal lobe, with a row of up to 6 pappose setae on inner margin and some serrate setae distally; propodus 1.6× longer than wide, hammer shaped, a few simple or bifid setae on disto-posterior margin, 2 rows of small comb scales on the disto-posterior corner; up to 16 long and short simple setae on disto-anterior margin; inner face with a row of 6 papposerrate setae and some scattered shorter simple setae; palm slope transverse, with up to 15 simple short setae; dactylus claw-like, with a plumose seta distally, polygonal pattern on the distal margin and short simple setae on the anterior margin.
Gnathopod 2 (Figure 14 (B)) subchelate, without comb scales or polygonal pattern; coxal plate 1.5× wider than long, with simple setae on the distal margin; basis with up to 5 long bifid setae on posterior margin, 1 short simple seta on anterior margin, and up to 2 bifid setae disto-posteriorly; ischium with 1 long simple seta disto-posteriorly; merus with up to 5 bifid setae on distal margin, with 1 seta almost midway to distal margin; carpus lobe slim, produced between merus and propodus, posterior margin with pappose setae, inner margin with 2 small pappose setae and disto-anterior margin with 2 long bifid setae; propodus almost triangular, palm slightly longer than posterior margin, slope oblique, with a slender posterior excavation, some short cuspidate setae with accessory setae, bifid setae and simple setae, anterior margin with a 4 short simple setae; dactylus claw-like, with one plumose seta distally.
Pereopods 3–7 (Figure 14 (C–G)) simple. Coxae with simple setae; coxa 3 similar to 1 and 2; coxa 4 1.2× longer than wide, excavated posteriorly; coxa 5 posterior lobe longer and narrower than anterior lobe; coxa 6 anterior lobe reduced; coxa 7 reduced. Pereopods 3, 4 and 5 subequal in size, pereopods 3 and 4 with 2 to 3 groups of 1 to 2 bifid or simple setae on the posterior margins of their basis, merus, and carpus, 2 bifid setae on the anterior margin of their merus, propodus with 4 to 5 groups of 1 to 3 simple or cuspidate setae on the posterior margin, and a plumose seta on the dactylus. Pereopod 6 and 7 subequal in size, ~1.2× longer than P3–P5; pereopods 5–7 with 2 to 6 groups of 1 to 3 simple, bifid, or cuspidate setae with accessory seta on the anterior margins of the basis, merus, carpus, and propodus, with 2 bifid or cuspidate setae with accessory seta on the posterior margin of the merus, groups of 3 to 6 bifid or cuspidate setae with accessory seta on the disto-anterior and disto-posterior margins of merus and carpus.
Pleopods (Figure 15 (E)) peduncle 0.7× the length of the rami, a pair of coupling spines; both rami with several long plumose setae.
Uropod 1 (Figure 15 (A)) peduncle 1.3× longer than inner ramus and 1.4× longer than the outer ramus, with 5 cuspidate setae with accessory seta; inner ramus slightly longer than outer ramus, with 3 cuspidate setae with accessory seta on dorsal margin and 6 cuspidate setae (3 shorter) apically, without curved seta; outer ramus with 3 cuspidate setae with accessory seta on dorsal margin and 4 cuspidate setae (2 longer, 2 shorter) apically.
Uropod 2 (Figure 15 (C)) 0.6× the total length of uropod 1, 1.1× longer than the peduncle of uropod 1, peduncle 0.8× the length of inner ramus and 0.9× the length of outer ramus, with 4 cuspidate setae with accessory seta; inner ramus 1.1× longer than outer ramus, with 3 cuspidate setae with accessory seta on dorsal margin and 5 cuspidate setae apically; outer ramus with 3 cuspidate setae with accessory seta on dorsal margin and 4 cuspidate setae (3 longer, 1 shorter) apically.
Uropod 3 (Figure 15 (B)) almost half the length of the peduncle of uropod 1 and subequal to the peduncle of uropod 2 and to the telson; peduncle with 4 cuspidate setae on outer distal margin; inner ramus absent; outer ramus subtriangular, shorter than peduncle, with 4 cuspidate setae (2 longer, 2 shorter) apically.
Telson (Figure 15 (D)) entire, subquadrate, as long as wide, apically rounded and with 2 short apical cuspidate setae and 3 small plumose setae on each side, symmetrically placed.
Coxal gills sac-like on pereonites 2–6. Sternal gills tubular on pereonites 2–7.
Female. (Figure 15 (F–G)) Body length 5.27 mm (N = 1); head length 0.44 mm (N = 1). Gnathopod 1 identical to the male. Gnathopod 2 (Figure 15 (G)) similar in size and shape to gnathopod 1; merus with 4 simple setae; carpus with 2 simple setae on the inner face; propodus elongated, with several long simple setae on the inner face and short simple setae on the palm; palm transverse; dactylus claw-like with a distal plumose seta. Telson (Figure 15 (F)) similar to the male, but with 3 simple setae apically.
Habitat
Freshwater pools in the Twilight Zone of Gruta Tobias de Baixo Cave. Troglobitic species.
Conservation
We propose H. caeca as endangered (EN) based on IUCN subcategory B1 (<5.000 km 2 in area of occurrence extension) and D1 (<250 mature individuals) (ICMBIO (Instituto Chico Mendes de ConservaÇão da Biodiversidade) 2013).
Remarks
Hyalella caeca specimens were collected in 1975 inside of Gruta Tobias de Baixo Cave and described in 1989 (Pereira 1989). It was the first hypogean species of the genus known from Brazil and the second worldwide. In the original description, the author briefly compared its morphology with that of Hyalella anophthalma Ruffo, 1957, pinpointing the absence of eyes and pigmentation, elongation of the antennas, reduced number of setae on a narrow ramus of uropod 3, and the morphology of the telson (Pereira 1989). Here we observe that the antennas are not longer than those of other species on average for the genus, and hence cannot be treated as a troglomorphy. When we compare H. caeca with H. ceciliae sp. n., the main differences are the size of antenna 1 relative to the body length, the relative sizes of articles 1–3 of the peduncle of antenna 1, the number of serrate setae on the outer plate of maxilla 1, the presence of comb scales and polygonal pattern on the male gnathopod 1 of H. caeca and the relative length of the pereopods. Table 1 lists other differences between H. caeca and Hyalella ceciliae sp. n. and other subterranean Hyalella species. It is worth mentioning that the material analysed was included in the description of H. spelaea, but these are not the same species.
description: Published as part of Penoni, Ludmila Rocha, Bichuette, Maria Elina, Borges, Rayssa Karolina Ferreira & Bueno, Alessandra Angélica de Pádua, 2025, New species of Hyalella Smith (Crustacea: Amphipoda: Hyalellidae): a contribution to the knowledge of a widely distributed genus in the Upper Ribeira karst, with redescription of the rare and endangered Hyalella caeca Pereira, pp. 195-226 in Journal of Natural History 59 (1 - 4) on pages 217-223, DOI: 10.1080/00222933.2024.2448565, http://zenodo.org/record/14764987