A new species of Melita Leach , 1814 ( Amphipoda : Hadzioidea : Melitidae ) from Patos Lagoon , southern Brazil

A new species of the family Melitidae Bousfield, 1973, Melita petronioi sp. nov., is described with material collected from Patos Lagoon, coast of the Brazilian state of Rio Grande do Sul, southern Brazil. The new species is the unique species of Melita Leach, 1814 in Brazilian waters with urosomites 1 and 2 lacking spines, but urosomite 2 bearing two sets of dorsal stout setae, and the uropod 3 with the outer ramus 2-articulate. It is the first Melita species recorded to the southern region of the country.


Introduction
The family Melitidae s.s.Bousfield, 1973 is composed by 39 genera distributed around the world (Lowry and Hughes, 2009;Senna and Serejo, in press).Amphipods of the superfamily Hadzioidea are very abundant and frequent in benthic samples.However, there are only six species of Melitidae recorded from Brazilian waters: Dulichiella anisochir (Krøyer, 1845); Cuneimelita danielle Senna and Serejo, 2012; Nuuanu peroa Senna and Serejo, in press; Melita orgasmos Barnard, 1940;M. mangrovi Oliveira, 1953;andM. lagunae Oliveira, 1953 (Senna andSerejo, 2012).One of these species, M. lagunae, has never been recorded after its original description.The other species, M. mangrovi, was recorded by Leite et al. (1980), from Ubatuba, São Paulo state, but this material seems to be lost now.There are two samples identified as M. mangrovi deposited at the Crustacea Collection of Museu Nacional (MNRJ 10679 and MNRJ 10401) from Lagoa According to Jarret and Bousfield (1996), the Melita species are grouped in two morphological groups: a "typical" group, with dorsal spines on urosome 1, and other one "atypical", lacking dorsal spines on urosome 1.Additionally, Melita also could be divided in two other groups: the first one presenting dorsal stout setae on urosome 2, and the other group with dorsal spines (Labay, 2003).
The new species described in this paper belongs to the group of species without spines on the urosome 1 and with stout setae on the urosome 2. It is the first species of Melita recorded to the Brazilian state of Rio Grande do Sul.

Material and Methods
The material examined was collected on drift algae in Ilha das Pombas, inside the Patos Lagoon, Rio Grande do Sul state, Brazil, in June 1999.The specimens were dissected under a stereoscopic microscope and their appendages and mouth parts were mounted in glycerol gel slides.Illustrations were made under an optic microscope with camera lucida and digitally prepared in Corel Draw X5, following an adapted protocol based on Coleman (2003).All the type material is preserved in ethanol 70% and it is housed at the Crustacea Collection of the Museu Nacional, Universidade Federal do Rio de Janeiro (MNRJ).The setal/spine classification adopted in this paper follows Watling (1989).Nomenclature of gnathopod palm is based on Poore and Lowry (1997).

Systematics
Order Amphipoda Latreille, 1816 Suborder Gammaridea Latreille, 1802 Superfamily Hadzioidea Karaman, 1943 Family  outer ramus 2-articulate, outer margin bearing six stout setae equally spread, article 2 vestigial, reduced to a rounded tip.Telson slightly wider than long, deeply cleft, apically subacute, with three stout setae on the inner margin and one stout seta on the outer margin, in each lobe.
Gnathopod 1, coxa about 1.6 times longer than wide, anterior margin convex, ventral margin setose; basis subrectangular, about 2.6 times longer than wide, anterior margin distally setose, posterior margin with four long slender setae; ischium about 1.4 times longer than wide; merus trapezoid shaped, posterior margin slightly convex, minutely setose; carpus elongate, subrectangular, about 2.3 times longer than wide, posterior margin densely setose; propodus subrectangular, about twice longer than wide, and about 0.4 times the carpus length, anterior margin convex, palm nearly transverse, strongly concave on the inner face of the propodus, posterodistal margin well produced, covered by several small scales; dactylus strong, curved, with a slender seta on the outer margin, apical nail present.Gnathopod 2, coxa about 1.5 times longer than wide, anterior margin convex, ventral margin setose; basis subrectangular, about twice longer than wide, anterior margin densely setose; merus subrectangular, posterodistal corner produced and subacute; carpus subtriangular, slightly wider than long, posterior margin setose; propodus suboval, robust, posterior margin densely setose, inner face with some rows of slender setae, palm acute, defined by two small stout setae, margin bearing several small stout setae and other one displaced near dactylus articulation; dactylus stout, curved, shorter than palm, apical nail present.Pereopod 3, coxa about twice longer than wide, anterior margin convex, ventral margin with small slender setae; basis, slightly curved, about 4 times longer than wide, anterior margin with two sets of long slender setae, posterior margin, first half with six slender setae; merus suboval, about 3 times longer than wide, anterior margin straight; carpus subrectangular, about 0.7 times the merus length, anterior margin setose, posterior margin naked; propodus slender, about as long as carpus, anterior margin bearing four stout setae; dactylus curved, stout, anterior margin with a stout seta, apical nail present.Pereopod 4 similar to pereopod 3, but coxa 4 with posteroventral lobe present, subquadrate.Pereopod 5, coxa bilobate, two lobes separated by a deep notch, anterior lobe rounded, naked; basis about 1.6 times longer than wide, slightly expanded posteriorly, anterior margin bearing eight small stout setae, anteroventral corner with one long stout seta; merus, about twice longer than wide, posterior margin convex, with four curved stout setae; carpus subrectangular, about twice longer than wide, anterior and posterior margins with two stout setae each; propodus slender, about 4.5 times longer than wide and 1.4 times longer than carpus, anterior and posterior margins without stout setae, posterodistal corner with a row of plumose setae; dactylus stout, curved, apical nail present.Pereopod 6, coxa bilobate, anterior lobe ventrally subacute, anterior margin almost straight, posterior lobe shallow and subquadrate; basis slightly expanded posteriorly, about 1.7 times longer than wide, anterior margin bearing ten small stout setae, anteroventral corner with one long stout seta; merus, about twice longer than wide, posterior margin convex, with three curved stout setae; carpus subrectangular, about three times longer than wide; propodus slender, about 5.5 times longer than wide and 1.6 times longer than carpus, anterior and posterior margins without stout setae, posterodistal corner with a row of plumose setae; dactylus stout, curved, apical nail present.Pereopod 7, coxa suboval, about 1.7 times longer than deep, anteroventral corner defined, posteroventral margin rounded; basis posteriorly expanded, anterior margin with five small stout setae, posterior margin with ten small stout setae, anteroventral corner with two stout setae; merus about twice longer than wide, anterior margin with three stout setae, posterior margin convex, with four stout setae, anteroventral and posteroventral corners with two stout setae each.
Epimeral plate 1 subquadrate, ventral and posterior margins naked.Epimeral plate 2 subquadrate, ventral margin with three small stout setae, posteroventral corner weakly produced, subacute.Epimeral plate 3 subquadrate, ventral margin with three small stout setae, posteroventral corner not produced.Urosomites 1 to 3 lacking posterodorsal spines.Urosomite 2 with two sets of three small stout setae on the posterodorsal margin.Uropod 1, peduncle elongate, 5.5 times longer than wide, dorsally setose, basofacial stout seta present; inner ramus slightly longer than outer, about 0.8 times the peduncle length, dorsal margin with three setae, apex subacute, bearing a set of two stout and three slender setae; outer ramus with two small setae dorsally, apex subacute, bearing a set of two stout and one slender seta.Uropod 2 short, peduncle subrectangular, about 1.8 times longer than wide, naked; rami subequal in length, about 1.2 times longer than peduncle.Uropod 3, peduncle about twice longer than wide, with stout setae on the posteroventral corner; inner ramus reduced, wedge-shaped, bearing four distodorsal setae; outer ramus 2-articulate, outer and inner margin densely setose, outer margin bearing six stout setae equally spread (1-1-1-1-1-1), article 2 reduced to a rounded tip.Telson slightly wider than long, deeply cleft, apically subacute, with three stout setae on the inner margin and one stout seta on the outer margin, on each lobe.
Geographic distribution: Known only from the type locality, Patos Lagoon, Rio Grande do Sul state, southern Brazil (Fig. 4).

Discussion
Melita petronioi sp.nov.belongs to the group of atypical species, cited by Jarret and Bousfield (1996), and formed by species without dorsal spines on urosome 1.It presents abdominal segments weakly armed dorsally, like M. koreana Stephensen, 1944, M. laevidorsum Stephensen, 1944, and M. nitidaformis Labay, 2003, all of them from the Asia Far East (Labay, 2003).The new species differs from M. nitidaformis by the shape of the propodus of gnathopod 2, with anterior and posterior margins subparallel, and the weakly developed posteroventral lobe on pereopods 5-7.It also differs from M. koreana by lack spines on the dorsal surface of urosomite 2, and differs from M. laevidorsum by the posteroventral corner of epimeral plate 3 subquadrate.
At the same time, it is part of the group with the uropod 3 outer ramus 2-articulate, like M. plumosa Zeidler, 1989, from the northern New South Wales, M. quadridentata  Yamato, 1990, from the Seto Inland Sea, Japan, or M. almagosa Sawicki and Holsinger, 2005, from subterranean groundwaters in Guam, eastern Philippine Sea, North Pacific Ocean.However, the second article present in the new described species is very shorter than in the cited 2-articulate species, reduced to a rounded tip, while these species have well developed second article.Karaman (1981) established the new genus Abludomelita supported in two plesiomorphic characters, one of them the 2-articulate outer ramus of uropod 3, such as shown in M. petronioi sp.nov.However, some authors, as Zeidler (1989), Yamato (1990), and Jarret and Bousfield (1996), do not recognize this criteria to define the genus Abludomelita, and keep several species with 2-articulate uropod 3 in the genus Melita.For the same reason, the subterranean freshwater genus Paraniphargus Tattersall, 1925 was synonymized with Melita by Sawicki et al. (2005), as suggested 74 years before by Schellenberg (1931).Abludomelita is considered a valid genus, but the new species described here is clearly located in the genus Melita.
Regarding the other three species of Melita recorded from Brazilian waters, one of them, M. orgasmos, presents a dorsal spine on the urosomite 1, while the other two species, M. lagunae and M. mangrovi, also lack abdominal dorsal spines, like the new species.Melita mangrovi presents two small setae dorsally on the urosome 2, while M. petronioi sp.nov.bears two sets of three small setae.On the other hand, seems that M. lagunae do not present these setae on the urosome 2, as shown in the original description (Oliveira, 1953).It is not easy to discuss about these two species because the descriptions made by Oliveira (1953) were not very detailed, as well as their illustrations.However, is possible to observe in Oliveira's illustrations that these two species present the uropod 3 with outer ramus 1-articulate.The other species recorded from Brazil, M. orgasmos, also presents outer ramus 1-articulate.Besides that, M. orgasmos presents epimeral plate 3 with posteroventral corner acutely produced, while the new species presents the epimeral plate 3 subquadrate and unproduced.Ledoyer (1979) defines the distribution of M. orgasmos being South Africa, India, and Indonesia.In fact, this species was recorded from São Paulo state coast by Wakabara et al. (1991) based in a faunistic study, without any description or illustration of the specimens.This material needs a revaluation to confirm its taxonomic identity.Thus, Melita petronioi sp.nov.can be distinguished from the other Brazilian species, being the unique presenting uropod 3 with 2-articulate outer ramus.
Additional comment: All examined specimens are infested with epibiont ciliates.Several crustacean groups, including amphipods, are found to be hosts (basibionts) of epibiont ciliates (Fernandez-Leborans et al., 2012).The epibiont ciliate species found attached to the examined material will be described in a subsequent publication.