Hyalella pseudoazteca, González & Watling, 2003

González, Exequiel R. & Watling, Les, 2003, A new species of Hyalella from Brazil (Crustacea: Amphipoda: Hyalellidae), with redescriptions of three other species in the genus, Journal of Natural History 37 (17), pp. 2045-2076 : 2067-2074

Hyalella pseudoazteca n. sp.

(figures 17–22)

Hyalella azteca: Pereira, 1983: 21–30 , figures 1–3, not synonymy, not H. azteca (Saussure) .

Type material. Holotype, male 6.3 mm (+ slides mount), Museu Nacional /UFRJ, Brazil, MNRJ 7611 . Paratypes, one male and one female (+ slide mount), Museu Nacional /UFRJ, Brazil, MNRJ 15585 .

Type locality. Reserva Ecologica de Taim , Rio Grande do Sul State, Brazil (32 ° 27 ∞ S, 52 ° 38 ∞ W).

Material examined. Reserva Ecologica de Taim, Rio Grande do Sul State, Brazil.

Diagnosis. Body with dorsal flanges on peraeonite 7 and pleonites 1 and 2. Coxa 4 excavated posteriorly. Eyes pigmented. Antenna 1 shorter than antenna 2. Antenna 2 half the body length. Mandible incisor toothed. Maxilla 1 palp minute, reaching less than half of the distance between base of palp and tip of setae on outer plate; inner plate slender, with two strong and pappose apical setae. Maxilla 2 inner plate with one strong pappose seta on inner margin. Gnathopod 1 propodus length less than twice maximum width (quadrangular), hammer-shaped, inner face with one to three pappose setae, setose scales on disto-posterior and disto-anterior border. Gnathopod 2 propodus ovate, palm shorter than posterior margin, slope oblique, anterior edge with a small process. Peraeopods 3 and 4 merus and carpus posterior margin with three hind marginal clusters of short setae; propodus posterior margin with five to eight groups of setae. Uropod 3 peduncle with two strong distal setae; outer ramus same length as peduncle, basal width twice or less tip of ramus. Telson as wide as long, apically pointed, with two closely spaced, long simple setae, symmetrically distributed, no additional apical setae present. Sternal gills on peraeonites 3–7.

Female. Gnathopod 1 smaller, and different shape to gnathopod 2. Gnathopod 2 different from male gnathopod 2 in shape and smaller, propodus length two to three times maximum width, normally subchelate, palm slightly reverse oblique.

Description of male. Size 6.3 mm. Body with dorsal flanges on peraeonite 7 and pleonites 1 and 2 (figure 17; figure 18 E). Epimeral plates 1–3 acuminate (figure 18 E). Coxae 1–4 subequal in size and shape, slightly overlapping. Acumination in coxae absent. Coxa 1 same as coxae 2 and 3. Coxa 3 narrower than 4. Coxa 4 deeper than wide, excavated posteriorly. Coxa 5 posterior lobe deeper than anterior lobe. Coxa 6 anterior lobe small.

Head smaller than first two thoracic segments, typically gammaridean, rostrum absent. Eyes pigmented, large, oval, located behind insertion of antenna 1.

Antenna 1 less than half of body length, shorter than antenna 2, longer than peduncle of antenna 2; peduncle longer than head, article 1 longer than article 2, article 3 shorter than article 1, and as long as article 2; flagellum with 10 articles, longer than peduncle, basal article not elongated; aesthetascs on flagellum, from article 5 distally (figure 19 A1).

Antenna 2 half of body length; peduncle slender, longer than head, article 4 shorter than article 5, setal groups on articles 4 and 5 scarce; flagellum with eight to nine articles, longer than article 5, basal article slightly elongated (figure 19 A2).

Basic amphipodan mandible (in the sense of Watling, 1993); incisor toothed; left lacinia mobilis with five teeth; setae row on left mandible with three main setae plus accessory setae; right mandible with two main setae plus accessory setae; molar large, cylindrical, triturative, accessory seta present. Labrum ventral margin slightly rounded to truncate. Lower lip outer lobes rounded without notches or excavations, mandibular projection of outer lobes round (figure 20 Ml, L, U).

Maxilla 1 palp uniarticulate, minute, less than half as long as the distance between base of palp and tip of setae on outer plate, distal setae absent; inner plate slender, smaller than outer plate, with two strong and pappose apical setae; outer plate with nine stout and serrate setae (figure 20 X1r). Maxilla 2 inner plate shorter, and subequal in width to outer plate, one strong pappose seta on inner margin, outer and inner plates with scarce setules (figure 20 X2r).

Maxilliped inner plates apically truncated, with one or two connate setae, pappose setae apically and medially; outer plates larger than inner plates, apically rounded, apical, medial and facial setae simple; palp longer than outer plate, with four articles; article 2 as wide as long, medial margin with long simple setae; article 3 outer distal face with few long simple setae, inner distal face with long plumose setae, inner distal margin with long setae, outer margin with one or two strong and long plumose setae; dactylus unguiform, subequal in length to third article, distal setae simple and shorter than nail, inner border with setae, distal nail present (figure 18 S).

Gnathopod 1 subchelate; carpus longer than wide, longer and wider than propodus, with weak posterior lobe, produced and forming a scoop-like structure, open to the medial side, inner face with one to three pappose setae, border pectinate and with several pappose setae; propodus length less than twice maximum width (quadrangular), hammer-shaped, with no setae on anterior border, inner face with one to three pappose setae, small triangular setae absent, setose scales on distoposterior and disto-anterior border, palm slope transverse, margin straight, posterior distal corner with robust setae; dactylus claw-like, with one to three endal setae, congruent with palm (figure 20 G1).

Gnathopod 2 subchelate; basis hind margin with one to three groups of setae; merus with fewer than seven setae on posterior margin, postero-distal margin concave, distal corner subacuminate; carpus posterior lobe elongated, produced between merus and propodus, border pectinate with several pappose setae; propodus ovate, disto-posterior and disto-anterior borders without setose scales, palm shorter than posterior margin, slope oblique, margin irregular, with few strong short setae, few long setae, and several medium-sized setae, anterior edge of palm with a small process, posterior distal corner with strong setae, and with cup for dactyl; dactylus claw-like, congruent with palm, with a few endal setae (figure 18 G2).

Peraeopods 3–7 simple. Peraeopods 3 and 4 merus and carpus posterior margin with three hind marginal clusters of short setae; propodus posterior margin with five to eight groups of setae; dactylus half length of propodus. Peraeopods 5–7 all similar in structure and slightly longer successively; dactylus less than half length of propodus. Peraeopod 5 subequal to peraeopod 4, basis posterior lobe deeper than wide, smaller than posterior lobe of peraeopod 7, merus with two posterior marginal setae, proximal setae smaller than more distal. Peraeopod 6 same length as peraeopod 4, basis posterior lobe deeper than wide, similar to posterior lobe of peraeopod 5, and smaller than posterior lobe of peraeopod 7. Peraeopod 7 subequal to peraeopod 6, basis posterior lobe wider than deep (figure 21 P3, P4, P5; figure 19 P6, P7).

Pleopods not modified; peduncle slender; longest ramus longer than peduncle.

Uropod 1 longer than uropod 2; peduncle longer than rami; rami subequal; inner ramus with one dorsal seta, and five distal setae, only one seta longer, male without curved setae on inner side of the ramus; outer ramus with three dorsal and four distal setae; peduncle setae present (figure 21 R 1).

Uropod 2 rami subequal; inner ramus with two dorsal and five distal setae; outer ramus with two dorsal and four distal setae; peduncle setae present (figure 18 R 2).

Uropod 3 longer than urosomite 3, longer than peduncle of uropod 1, shorter than peduncle of uropod 2; peduncle quadrate, same width as ramus, with two strong distal and no marginal setae; inner ramus absent; outer ramus uniarticulate, as long as peduncle, proximally twice as wide or less than distally, with four simple apical slender setae, and one connate seta (figure 18 R 3).

Telson as wide as long, entire, apically pointed, with two closely spaced, long simple setae, symmetrically distributed on the apical margin, no additional apical setae present (figure 20 T).

Coxal gills sac-like, on peraeopods 2–6. Sternal gills tubular, on peraeonites 3–7.

Characters of female that differ from male. Size 4.6 mm. Antenna 1 flagellum with seven articles. Antenna 2 similar in shape to male, flagellum with nine articles. Gnathopod 1 smaller, and different shape to gnathopod 2; similar to male gnathopod 1 in size and shape. Gnathopod 2 different from male gnathopod 2 in shape and smaller, propodus length two to three times maximum width, normally subchelate, palm slightly reverse oblique (figure 22 fG1, fG2).

Habitat. Freshwater, epigean, littoral.

Remarks. This new species was determined as H. azteca by Pereira (1983), mainly for the supposed presence of dorsal carinae on peraeonite 7 and pleonites 1 and 2. The lack of an accurate description of H. azteca at the time of Pereira’s (1983) work made her mistakenly consider the flanges of the Brazilian species as the carinae of H. azteca . After examining part of the material that Pereira (1983) had on hand, and comparing it with the redescription of H. azteca (Gonzalez and Watling, 2002) , it was clear that the Brazilian material corresponds to a new species. Hyalella pseudoazteca differs from H. azteca in the shape of the propodus of gnathopod 2 in male and female, having two pappose setae on the palp of maxilla 1, one big seta on inner margin of inner plate of maxilla 2, and a large eye. H. azteca and its allied species have three setae on inner plate of maxilla 1 and two setae on the inner border of inner plate in maxilla 2.