A new species of freshwater amphipod (Crustacea, Amphipoda, Hyalellidae) from state of Rio Grande do Sul, Southern Brazil

The current study describes a new species of Hyalella found in a natural pond at the municipality of Palmeira das Missões, located in the northwestern region of state of Rio Grande do Sul, southern Brazil. The new species differs from other species found in state of Rio Grande do Sul (Hyalella bonariensis, H. castroi, H. kaigang, H. imbya, H. georginae, H. gauchensis, H. montenegrinae and H. pampeana) in the type and number of setae on uropods, on telson and on the inner face of gnathopod 1. Besides, Hyalella palmeirensis is morphologically similar to H. curvispina, especially in the shape and number of setae of uropods. However, H. palmeirensis differs from H. curvispina in having only two simple setae on telson, the inner face of gnathopod 1 with five serrate setae and only the posterior distal margin with denticles in comb-scales, and especially by the tubular sternal gills, present on segments 3 to 7. These new records increase from 11 to 12 the number of species known from state of Rio Grande do Sul.


Introduction
Amphipoda is a successful group of peracaridan crustaceans known in several aquatic environments, including freshwaters where it exerts dominance of the benthic community of lakes (Ishikawa and Urabe 2002;Rodrigues 2016). The latest classification of the Order is shown by Lowry and Myers (2013), and these authors presented a new Suborder called Senticaudata, comprising almost all freshwater Amphipoda species and many marine species that previously belonged to the defunct Suborder Gammaridea.
Brazil has the greatest number of Hyalella species described in the world, 27 in total (Bueno et al. 2013;Bueno et al. 2014;Cardoso et al. 2014;Rodrigues et al. 2014;Streck et al. 2017;Rodrigues et al. 2017, Bastos-Pereira et al. 2018). According to Bueno et al. (2014) and Streck et al. (2017) the state of Rio Grande do Sul (Southern Brazil) is the region with the highest species diversity in the country, counting 11 described species. With the finding of this specie the state of Rio Grande do Sul account now with 12 Hyalella species, the same number of species observed in all Southeast region of Brazil.
A new species of Hyalella is described from the municipality of Palmeira das Missões, northwest region of state of Rio Grande do Sul, southern Brazil.

Material and Methods
The municipality of Palmeira das Missões is located at the northwest region of state of Rio Grande do Sul, Southern Brazil. The specimens were collected in August/2012 and the sampling was made with the aid a hand net, with authorizations of the Instituto Chico Mendes de Conservação da Biodiversidade (MMA; ICMBio; SISBIO nº 32726-1).
Head length of the animals was measured through an optic microscope with a millimetric scale. Adult males and females were preserved in ethanol 70%, colored with Rose Bengal and dissected. A total of 15 individuals (10 males and 5 females) were dissected and the appendices were mounted on permanent slides. Illustrations were made using photos and the CorelDraw program.
The description was made based on main morphological characteristics such as the gnathopods, uropods and telson, according to González et al. (2003a, b), González et al. (2006), Cardoso et al. (2011), and. The terminology used for the setae of the appendices follows Zimmer et al. (2009).
The description was based on male paratype and female allotype. The type material is deposited in the Museu Nacional do Rio de Janeiro (MNRJ). Diagnosis. Body surface smooth. Eyes round, pigmented. Antenna 1 shorter than antenna 2, flagellum with 11/12 articles and longer than peduncle, two aesthetascs occurring distally on flagellum after article 5. Antenna 2 flagellum with 10/11 articles and longer than peduncle. Maxilla 1 palp uniarticulate, short, longer than wide, inner plate shorter and slender than outer plate, with two long apical papposerrate setae, and some setules on the inner margin; outer plate with nine serrate setae. Maxilla 2 inner plate with only one long and strong papposerrate seta and several simple and serrate setae. Gnathopod 1 with inner face with five serrate setae, posterior distal margin with denticles in comb-scales, one cuspidate seta and some simple setae. Gnathopod 2 propodus longer than wide and with posterior margin of small 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 the lobe of propodus; carpus wider than long, posterior lobe elongated, with pectinate border and one row of serrate setae, without polygonal pattern or comb-scales. Pleopods rami with long plumose setae. Uropod 1 inner ramus with a long-curved seta followed by a row of five small cuspidate setae with an accessory seta. Uropod 2 inner ramus apex with five cuspidate setae with an accessory seta and two cuspidate simple setae. Uropod 3 peduncle with three cuspidate setae with accessory setae apically, small cuspidate setae and simple setae distributed along the peduncle and ramus. Telson (male) longer than wide, with two apical simple setae, and three plumose setae close to each simple seta. Coxal gills sac-like present on segments 2 to 6 and sternal gills tubular, presents on segments 3 to 7.
Antenna 2 (Fig. 1c) peduncle less than half body length, with very few setae; flagellum with 10/11 articles and longer than peduncle. Upper lip (Fig. 1d) margin rounded, distal border covered by several setules on dorsal and ventral faces.
Basic amphipodan mandible ( Fig. 1e) (in sensu of Watling 1993), without palp; incisor toothed; left lacinia mobilis with five teeth and with three pappose setae; molar process large, cylindrical and with large accessory seta.
Lower lip (Fig. 1f) outer lobes rounded without notches or excavations, with several setules on dorsal and ventral faces.
Maxilla 1 (Fig. 1g) 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 uniarticulate, shorter and slender than outer plate, with two long apical pappose setae. Outer plate uniarticulate, with 9 serrate setae.
Maxilla 2 (Fig. 1h) inner plate with one long and strong papposerrate seta, several simple and serrate setae; outer plate with one row of simple setae.
Maxilliped (Fig. 1i) inner plates apically truncated, with three connate setae and pappose and simple setae apically and medially; outer plates larger than inner plates, apically truncated, apical, medial, and facial setae simple. Palp of four articles with simple setae and few pappose setae; dactylus unguiform, shorter than propodus, with simple setae and comb-scales.
Gnathopod 1 (Fig. 2a) subchelate; dactylus claw-like, with denticles in comb-scales and one plumose seta dorsally; propodus longer than wide, width about 3⁄4 of maximum length (rectangular), hammer-shaped, palm slope slightly oblique and margin sinuose with several simple setae, posterior distal margins with comb scales, one cuspidate setae and some simple setae, anterodistal margin without comb scales, but with six or seven simple setae, propodus inner face (ventral) with five serrate setae; 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; basis, ischium and merus with simple setae dorsally, without comb-scales posterodistally; coxal plates longer than wide.
Gnathopod 2 (Fig. 2b) subchelate; dactylus claw-like, short, not reaching the lobe of propodus, with one plumose seta dorsally, without comb-scales; propodus longer than wide (ovate), propodus length 1.5 times the maximum width, posterior margin of lobe almost straight and covered with denticles in comb-scales; palm margin convex, with several cuspidate setae with accessory setae and simple setae, posterior distal corner with few simple setae; carpus wider than long, posterior lobe elongated, with pectinate border with one row of serrate setae and without polygonal pattern or comb-scales; ischium and merus with few simple setae on posterodistal margin; basis, ischium and merus without comb-scales on posterior margin; coxal plate wider than long.
Uropod 1 (Fig. 4b) peduncle slightly (1.2 times) longer than rami, with four cuspidate setae with an accessory seta dorsally; inner ramus longer than outer ramus; inner ramus with two dorsal cuspidate setae with an accessory seta, male with a curved seta followed by a row of five small cuspidate setae with an accessory seta, two cuspidate setae apically; outer ramus with three dorsal cuspidate setae with an accessory seta and four cuspidate setae apically (two of them with an accessory seta).
Uropod 2 (Fig. 4c) shorter than uropod 1; peduncle rectangular with similar size as rami, with four cuspidate setae with an accessory seta dorsally; inner ramus slightly longer than outer ramus, with two dorsal cuspidate setae with an accessory seta and seven cuspidate setae apically (five with an accessory seta); outer ramus with two dorsal cuspidate setae with an accessory seta and apex with four cuspidate setae (two with an accessory seta).
Uropod 3 (Fig. 4d) peduncle slightly longer than wide, wider than ramus, with three cuspidate setae with an accessory seta and one simple seta apically, two simple setae distributed along the peduncle; ramus with five simple setae and a short, strong cuspidate setae.
Telson (Fig. 4e) is longer than wide, with two long simple setae and three plumose setae close to each simple seta.
Gnathopod 1 (Fig. 5a) similar to male gnathopod 1, similar size to gnathopod 2; dactylus with comb-scales and plumose seta; propodus longer than wide, hammer-shaped, inner face with five serrate setae and two long simple setae and several short simple setae , anterior distal margin without comb-scales but two simple setae and distally with six or seven short simple setae, posterior distal margin with comb-scales and two simple setae and posterior distal corner with one strong cuspidate seta; carpus longer than wide, with lateral distal lobe produced and forming a scoop-like structure, posterior lobe margin with polygonal pattern and with serrate setae and without comb-scales; base, merus and ischium without comb-scales on posterior margin.
Gnathopod 2 (Fig. 5b) similar in size to gnathopod 1, but the propodus of gnathopod 2 is slightly longer than gnathopod 1; different to male gnathopod 2 in shape and smaller; dactylus with comb-scales and one plumose seta; propodus rectangular, longer than wide, inner face with four serrate setae and two long simple setae and several short simple setae, palm transverse, posterior distal corner with one strong cuspidate seta, posterior distal margins with comb-scales and two simple setae and anterior margin without comb-scales; base, merus and ischium without comb-scales on posterior margin. Telson similar in shape to male, with two long simple setae and three plumose setae close to each simple seta.
Habitat. Freshwater, epigean. Hyalella palmeirensis was found in a natural pond of shallow depth (around 40 cm) ( Fig. 6a and 6b). The pond contains a large amount of macrophytes of the genus Egeria which were used as shelter for the specimens of H. palmeirensis.
Etymology. The specific name, palmeirensis, refers to native residents of Palmeira das Missões municipality, southern Brazil.
Remarks. We noted using the taxonomic key of       Hyalella palmeirensis is similar to H. curvispina, especially in the shape and number of setae of uropods. However, H. palmeirensis differs of H. curvispina in having only two simple setae on telson, inner face of gnathopod 1 with five serrate setae and only the posterior distal margin with denticles in comb-scales, and especially by tubular sternal gills present on segments 3 to 7.
The new species Hyalella palmeirensis resembles H. misionensis, from the Province of Misiones in Argentina, in the telson (male) with two long apical simple setae. However, it differs in the curved seta on the inner ramus of uropod 1, inner face of propodus of gnathopod 1 and sternal gills. The area where H. misionensis was found is geographically close to Brazil. Comparisons between morphological characters of Hyalella species of Rio Grande do Sul are presented in Table 1.

Discussion
The new species described here, improves the diversity of Hyalella in the Southern region of Brazil, increasing the number of species found in the region, to 14, whereas 12 of them are observed in the state of Rio Grande do Sul, the same number of all southeastern region of Brazil Cardoso et al. 2014;Rodrigues et al. 2014).
In addition to morphological differences, other evidence that H. palmeirensis is a distinct species from others of the genus comes from a matrix of pairwise nucleotide sequence divergences using concatenated genes 16 S (~650bps), 12 S (~550bps) and H3 (~375bps) (Rodrigues 2016 (Streck et al. 2017). Moreover, Rodrigues (2016) estimated the phylogeny of Hyalella reconstructed by Bayesian analysis and according to it, H. palmeirensis is statistically The species Hyalella palmeirensis lives in association with macrophytes in a natural pond of shallow depth. The pond contains a large amount of macrophytes of the genus Egeria, which are used as shelter by H. palmeirensis. However, H. palmeirensis occurs in a natural pond surrounded by the cultivation of many types of crops, which could be considered a threat to this species as the pesticides used during cultivation can be harmful to the amphipods. Agricultural expansion, especially rice and soybean, is one of the main factors that affect and hinders conservation, because this activity not only remove the original vegetation for cultivation but also often bring out chemicals for soil remediation, pest control or fertilization, and cause fragmentation and deterioration of these ecosystems (Maltchik and Rolon 2010;Rodrigues et al. 2012).