Hyalella georginae, Castiglioni, 2017

Morgana Tais Streck, Giovanna Monticelli Cardoso, Stella Gomes Rodrigues, Daniel Angelo Sganzerla Graichen & Daniela Da Silva Castiglioni, 2017, Two new species of Hyalella (Crustacea, Amphipoda, Hyalellidae) from state of Rio Grande do Sul, Southern Brazil, Zootaxa 4337 (2), pp. 263-278 : 264-269

Hyalella georginae n. sp. Streck & Castiglioni

Material examined: Holotype male, body length = 11.28 mm, head length = 0.90 mm (MNRJ 25898); Allotype female ( MNRJ 25899 ). Brazil, state of Rio Grande do Sul, Palmeira das Missões municipality, Sítio Taqui (27°57'52.79"S – 53°14'02.59"W), August, 10, 2012, Castiglioni, D.S. coll.

Paratypes: MNRJ 25900 (20 males and 20 females), CCUFLA 0 391. All specimens with the same data as the holotype, August, 10, 2012, Castiglioni, D.S. coll. Mean body length of male paratypes: 11.82 ± 2.88 mm and female paratypes: 7.84 ± 1.31 mm.

Type-locality. Brazil, state of Rio Grande do Sul, Sítio Taqui (27°57'52.79"S – 53°14'02.59"W), state of Rio Grande do Sul, Palmeira das Missões municipality, small spring (Várzea river basin), 540 meters of altitude, August, 10, 2012.

Diagnosis. Maxilla 2 inner plate with 9–10 serrulate setae and two robust papposerrate apical setae. Gnathopod 1 posterior lobe of carpus with one row of serrate setae and without comb-scales, propodus inner face with nine serrate setae, hammer-shaped, posterior and anterior distal margins with comb-scales. Gnathopod 2 carpus wider than long, posterior lobe with pectinate border and one row of serrate setae; propodus longer than wide and with posterior margin of lobe covered by denticles in comb-scales; palm smooth and sub-equal to posterior margin of propodus, slope oblique, palm margin convex; dactylus claw-like, short, not reaching lobe of propodus. Uropod 1 inner ramus of male with curved setae followed by four small cuspidate setae with accessory seta. Uropod 2 inner ramus apex with seven cuspidate setae. Uropod 3 peduncle with nine cuspidate setae with accessory setae apically. Telson as long as wide, with seven apical cuspidate setae with accessory seta distributed in two clusters (two setae and other side five four setae) and four plumose setae laterally. Coxal gills sac-like present on pereonites 2 to 6 and sternal gills tubular on pereonites 2 to 7.

Description of male. ( Fig. 1 ) Mean body length: 11.82 ± 2.88 mm, mean head length: 0.93 ± 0.24 mm (n=20). Body surface smooth; epimeral plates not acuminate.

Head slightly longer than first pereonite, rostrum absent. Eyes round, pigmented ( Fig. 1 ).

Antenna 1 ( Fig. 2 ) shorter than antenna 2, less half body length; peduncle not surpassing head length, article 2 with two distal plumose setae; flagellum with 15 articles, longer than peduncle; two aesthetascs per article occurring distally on flagellum after article 2.

Antenna 2 ( Fig. 3 ) peduncle not surpassing first pereonite, less than half body length, article 1 and 2 with cluster of simple setae on distal margin, article 2 with one plumose seta on lateral margin, article 3 with cluster of simple setae on distal margin and several simple setae along lateral margin; flagellum with 16 articles, longer than peduncle, basal article elongated.

Upper lip ( Fig. 4 ) margin rounded, distal border covered by several setules on dorsal and ventral faces.

Basic amphipodan mandible ( Fig. 5 ) (in sensu of Watling 1993), without palp; incisor toothed; left lacinia mobilis with five teeth and setae row on left mandible with three pappose setae; molar process large, cylindrical and with large accessory seta.

Lower lip ( Fig. 6 ) lobes rounded, with several setules on dorsal and ventral faces.

Maxilla 1 ( Fig. 7 ) palp uniarticulate, short, longer than wide, reaching less than half length the distance between the base of the palp and tip of setae on outer plate; inner plate slender, shorter than outer plate, apex with two papposerrate setae, and setules on the inner margin; outer plate with nine long serrate setae.

Maxilla 2 ( Fig. 8 ) inner and outer plates of similar sizes; inner plate with ten serrulate and several simple apical setae and two robust papposerrate apical setae; outer plate with several apical simple setae; outer and inner plates with several setules.

Maxilliped ( Fig. 9 ) inner plate apically rounded, longer than wide, with three cuspidate setae, apex and inner margins with pappose and simple setae; outer plate with simple setae apically; palp with four articles, with simple and pappose setae; dactylus unguiform, shorter than propodus, with simple setae.

Gnathopod 1 ( Fig. 10 ) subchelate; coxal plate wider than long; basis, ischium and merus with simple setae dorsally, with comb-scales posterodistally; carpus longer than wide, slightly longer than propodus, with strong lateral distal lobe produced and forming a scoop-like structure, posterior lobe of carpus with one row of serrate setae and without comb-scales, and ventral face with twenty serrate setae; propodus longer than wide, propodus width about 3⁄4 of maximum length (rectangular), hammer-shaped, inner face with nine serrate setae and several simple setae, posterior and anterior distal margins with denticles in comb-scales and simple setae, disto-anterior border with cluster of simple setae; palm slope oblique with cluster of simple setae on posterior distal corner; dactylus claw-like, with denticles in comb-scales and one plumose seta dorsally.

Gnathopod 2 ( Fig. 11 ) subchelate; coxal plate wider than long; ischium and merus with few simple setae on disto-posterior margin; basis, ischium and merus with one row of denticles in comb-scales on posterior margin; carpus wider than long, posterior lobe elongated, with pectinate border and one row of serrate setae, without polygonal pattern or comb-scales; propodus longer than wide, propodus length 1.5 times maximum width, posterior margin of lobe covered by denticles in comb-scales; palm smooth and sub-equal to posterior margin of propodus, slope oblique, palm margin convex, with several cuspidate setae and simple setae, posterior distal corner with cuspidate setae and simple setae; dactylus claw-like, short, not reaching lobe of propodus, with one plumose seta dorsally, without comb-scales.

Pereopods 3 to 7 ( Figs. 12–16 ) simple, with simple setae on border; ischium, merus, carpus and propodus posterior margin with cluster of simple and cuspidate setae; dactylus half-length of propodus, unguiform; pereopod 3 and 4 with similar sizes; pereopod 5 smaller than others; pereopod 6 smaller than pereopod 7.

Pleopods ( Fig. 17 ) peduncle shorter than rami, with two coupling spines; both rami with several short plumose setae.

Uropod 1 ( Fig. 18 ) peduncle slightly (1.2 times) longer than rami, with six cuspidate setae with accessory seta dorsally; inner ramus longer than outer ramus; inner ramus with four dorsal cuspidate setae with accessory seta, male with one curved seta followed by four small cuspidate setae with accessory seta, apex with four cuspidate setae (one of them with accessory seta); outer ramus with five dorsal cuspidate setae with accessory seta and four cuspidate setae apically (two of them with accessory seta).

Uropod 2 ( Fig. 19 ) shorter than uropod 1; peduncle rectangular as long as rami, with six cuspidate setae dorsally; inner ramus slightly longer than outer ramus, with five dorsal cuspidate setae, apex with seven cuspidate setae; outer ramus with six cuspidate setae dorsally and apex with four cuspidate setae.

Uropod 3 ( Fig. 20 ) shorter than other uropods; peduncle slightly longer than wide, wider than ramus, with cuspidate setae apically (nine of them cuspidate setae with accessory setae); ramus uniarticulate, sub-equal to peduncle, with eight simple setae and one short cuspidate seta apically, two cuspidate setae with accessory seta and five simple setae distributed along the ramus.

Telson ( Fig. 21 ) entire, apically rounded, as wide as long, with seven apical cuspidate setae with accessory seta distributed in two clusters (two setae and other side five four setae) and four plumose setae laterally.

Coxal gills sac-like present on pereonites 2 to 6 and sternal gills tubular on pereonites 2 to 7.

Female. Mean body length: 7.84 ± 1.32 mm, mean head length: 0.84 ± 0.14 mm (n=20). Antenna 1 flagellum with 12 articles. Antenna 2 flagellum with 13 articles. Gnathopod 1 ( Fig. 22 ) similar to male gnathopod 1, wider than gnathopod 2; carpus longer than wide, with lateral distal lobe posterior lobe with polygonal pattern, one row of serrate setae and denticles in comb-scales on margin, and ventral face with seven serrate setae; propodus longer than wide, hammer-shaped, inner face with ten serrate setae, anterior and posterior distal margins with combscales, posterior distal corner with simple setae and one strong cuspidate setae; dactylus with comb-scales and one plumose seta. Gnathopod 2 ( Fig. 23 ) carpus longer than wide, posterior lobe with polygonal pattern and one row of serrate setae, ventral face with three serrate setae; propodus rectangular, longer than wide, inner face with seven serrate setae and several simple setae, palm transverse, posterior distal margin with comb-scales, one short cuspidate setae and some simple setae on the posterior distal corner, anterior distal margin without comb-scales; dactylus with comb-scales and one plumose seta. Telson similar in shape to male, but with distinct pattern of distribution of the cuspidate setae with accessory seta (two clusters with three setae each, and the other side with four setae) and four plumose setae laterally.

Habitat. Freshwater, epigean. The specimens of H. georginae were found in a spring shaded by small trees and surrounded by grasses and pteridophytes ( Fig. 47 ). Despite macrophytes of the genus Lemna sp. occur in the spring, the specimens of the new species were found associated with the sediment.

Conservation. The spring where H. georginae was found is well preserved and it is located in a rural property, which there is no cultivation of soybeans, wheat or barley (the most commons crops in the region). Furthermore, the water from the spring is collected to be used for human consumption, so is beneficial for the residents of the property keep this environment protected.

Etymology. The species epithet " georginae " is in compliment to Dr. Georgina Bond-Buckup for her outstanding contribution to the study of Hyalella and other freshwater crustaceans in Brazil.

Remarks. We noted that H. georginae differs from all Brazilian species of Hyalella using the taxonomic key of Rodrigues et al. (2014). The new species resembles to H. montenegrinae , H. curvispina , H. castroi , H. pseudoazteca , H. kaingang , H. pleoacuta , H. carstica Bastos-Pereira & Bueno, 2012 and H. xakriaba Bueno & Araujo, 2013 by the presence of a curved seta on the inner ramus of uropod 1 of the males. However, H. georginae differs from H. montenegrinae and H. carstica by presenting sternal gills on segments 2–7 and more than two apical setae on telson, respectively. The new species differs from H. curvispina , H. castroi , H. pseudoazteca , H. kaingang and H. pleoacuta by the fact that the dactylus of gnathopod 2 is shorter than propodus palm. Despite H. georginae resembles in the length of the dactylus of gnathopod 2 to H. xakriaba and H. brasiliensis , the new species differs from H. xakriaba by presenting simple apical setae on outer ramus of uropod 3 and from H. brasiliensis by showing nine serrate setae on inner face of propodus of gnathopod 1. Besides, H. georginae present a peculiar pattern of setae on peduncle and ramus of uropod 3.

Figures

FIGURES 1 – 9. Hyalella georginae n. sp. Paratype male (MNRJ 25900): (1) Habitus from holotype (MNRJ 25989), body length: 11.28 mm; (2) Antenna 1; (3) Antenna 2; (4) Upper lip; (5) Mandible; (6) Lower lip; (7) Maxilla 1; (8) Maxilla 2; (9) Maxilliped; Scales: (1 – 3) represents 0.5 mm; (9) 0.5 mm; (4 – 8) 0.2 mm.

FIGURES 10 – 11. Hyalella georginae n. sp. Paratype male (MNRJ 25900); (10) Gnathopod 1; (11) Gnathopod 2; Scales: (10 – 11) represents 0.5 mm.

FIGURES 12 – 16. Hyalella georginae n. sp. Paratype male (MNRJ 25900); (12) Pereopod 3; (13) Pereopod 4; (14) Pereopod 5; (15) Pereopod 6; (16) Pereopod 7; Scales: (12 – 16) represents 0.5 mm.

FIGURES 17 – 21. Hyalella georginae n. sp. Paratype male (MNRJ 25900); (17) Pleopod; (18) Uropod 1; (19) Uropod 2; (20) Uropod 3; (21) Telson; Scales: (17) represents 0, 5 mm; (18 – 21) 0.2 mm.

FIGURES 22 – 23. Hyalella georginae n. sp. Allotype female (MNRJ 25899); (22) Gnathopod 1; (23) Gnathopod 2; Scales: (22 – 23) represents 0.5 mm.

FIGURES 47 – 48. (47) Type-locality of Hyalella georginae sp. n. Streck & Castiglioni, showing the spring shaded by trees and surrounded by grasses and pteridophytes. Note that water of the spring is collected through a pipe by local residents for human consumption. (48) Type-locality of Hyalella gausensis sp. n. Streck & Castiglioni, showing the artificial pond of shallow depth Note the large amount of macrophytes of the genus Salvinia, which are used as shelter for the specimens of the new species.