A new Dendrocephalus ( Crustacea , Anostraca , Thamnocephalidae ) from Rio Grande do Sul State , Brazil

Dendrocephalus riograndensis n. sp., a new species of fairy shrimp, is described from a single temporary pool in Santa Vitória do Palmar, Rio Grande do Sul, Brazil. Males are readily separated from all other Dendrocephalus Daday, 1908 species by the form of the frontal appendage and the form of the first thoracopods. This new species is most similar to Dendrocephalus goiasensis Rabet & Thiéry, 1996 and could be confused with this species. This new species appears to be endemic to Rio Grande do Sul. Key worDs Fairy Shrimp, endangered species, identification key, Laguna dos Patos Ecoregion.

This area is subtropical, with an average temperature of 13°C in the coldest months ( June and July) and above 22°C in the warmest months ( January and February).The average annual rainfall (1200-1500 mm) is uniform in all seasons, but varies greatly in different years (Nobre et al., 1986).

A new Dendrocephalus
Nauplius, 24: e2016014 Dendrocephalus riograndensis n. sp. was found in a small (~120 m²), shallow (< 60 cm depth) temporary pool, exposed to direct sunlight, near the margin of Mirim lagoon.The water tends to be humic.The pool is in a small depression, in grassland areas of private farms.The aquatic vegetation was abundant (especially submerged macrophytes), but D. riograndensis n. sp. was only observed in the deepest portions of the pool, where there was no vegetation.
Dendrocephalus riograndensis n. sp.co-occurs with the annual fish Austrolebias charrua Costa & Cheffe, 2001; an endangered endemic species in Brazil and Uruguay (Loureiro et al., 2013;MMA, 2014).Dendrocephalus riograndensis n. sp.suffers from the same problems that led A. charrua to be considered endangered: habitat loss and fragmentation due to their natural habitat converted to rice agriculture.
Etymology.The name "riograndensis" refers to the state of Rio Grande do Sul where this species was discovered.
Diagnosis.(Figs. 1, 2A-E) Typical Dendrocephalus.Male bearing eye spine; second antenna, proximal antennomere with medial projection, bearing small denticles; frontal appendage bearing several spines along the anterior margin, between primary branches; branch 1V anterior sub-branch acute, posterior subbranch in subdistal position; branch 2V posterior surface deeply concave, bearing two nearly apical cell pads and one cell pad on medial surface; branch 2D sub-branch I greater than twice the length of subbranch II; sub-branch I and II with medial longitudinal row of close set, fine spines, joining at branch 2D base; branch 2A apex podiform; thoracopod I with single medial spiniform process; thoracopod I mediodistal corner triangular; thoracopod I proximolateral margin greatly elongated, arcuate, spiniform projection.
Description.Average length of preserved material: 18.6 mm from apex of head to apex of telson (males averaging 18.8, n = 7; females averaging 18.4, n = 7).
Frontal (cephalic) appendage prominent, typical of genus (Fig. 1A), when expanded reaching thoracomere X or XI.Frontal appendage basal trunk and primary branches anterior margin bearing six spines at bifurcation point, spines increasing in size from proximal to distal.Primary branch from bifurcation to branch 1V base twice as long as trunk, bearing four to six dorsal spines.Primary branch from branch 1V base to branch 2V base approximately one third length of primary branch from bifurcation to branch 1V base, bearing medial, longitudinal row of small spines, decreasing in size distally.
Branch 2D base broadly triangular (Fig. 1A).Sub-branch I length subequal to primary branch from bifurcation to branch 1V, subcylindrical basally, tapering to acute apex.Sub-branch I anterior surface with longitudinal row of four large, long, recurved spines.Sub-branch I medial surface with longitudinal row of small, close set spines, extending from branch 2D base, to sub-branch I apex.Sub-branch I distal 50% covered in small scattered spines; apex tipped with single small spine.Sub-branch II length approximately 50% of sub-branch I, tapering to rounded apex.Subbranch II posterior surface with longitudinal spine row, with proximal first two spines three to four times size and length of remaining spines.Sub-branch II medial surface with longitudinal row of small, close set spines, extending from branch 2D base, joining small spine row from sub-branch I, extending to sub-

A new Dendrocephalus
Nauplius, 24: e2016014 branch II apex.Sub-branch II anteriomedial surface with longitudinal row of spines.Sub-branch III with two large basomedial spines, proximal spine twice as large as distal spine.Sub-branch III posterior surface with longitudinal spine row on distal 50%.Sub-branch III apex asymmetrical, subtruncate to subangular.
Thoracopod I endopod (Fig. 2C) bearing single small, medial, spiniform projection.Distomedial corner triangular, bearing few filiform setae on medial margin.Distal margin deeply and broadly emarginate.Distolateral corner broadly subquadrate, lobiform, bearing distal, marginal row of four or five long spines, each separated by approximately one fourth their length, lateral margin with row of four or five short, stout spines.Proximolateral corner produced as elongated, spiniform projection, curving ventrally, apex with stout spine.
Female.As typical for the genus.Head rounded, anterolateral corners not projecting over eyestalk base.First antenna 1.3 times length of second antenna.Second antenna broadly elliptic, lamellar.Thorax smooth.Thoracopods as in male, except first three thoracopods with endopodites not modified.Thoracopod XI with exopodite narrowly elliptic, curving dorsally, and margined with plumose setae.Brood pouch fusiform, extending to distal margin of postgenital abdominal segment IV.
Distribution and habitat.To date, D. riograndensis n. sp. is known only from the type locality (Fig. 2G).The vicinity is primarily rice farming, which has resulted in the loss and degradation of most temporary wetlands in southern Brazil (Volcan et al., 2015).The type locality of D. riograndensis n. sp. is an 'island' in the middle of rice agriculture.The site is located on a private farm that cultivates rice and cattle.The type locality is not protected, but due to the high concentration of temporary pools in the region, this species may occur at Taim ecological station (about 15 km to the north), a federal conservation unit.Presently, this species meets the criteria under the IUCN Red List (IUCN, 2001) as Critically Endangered (CR), with the area of occupancy less than 10 km 2 , known only to exist at a single site (B2), and projected decline in extent of occurrence, occupancy and quality of habitat (ab).

DisCussion
Male D. riograndensis n. sp. is separated from all other reported Dendrocephalus species by the form

A new Dendrocephalus
Nauplius, 24: e2016014 of the second antennae, the frontal appendage and the thoracopod I endopods.In the key provided by Chaves et al. (2011) D. riograndensis n. sp.would key to D. goiasensis.The two species are remarkably similar, sharing a basically similar frontal appendage.However, they differ in the form of branch 2V, which bears four apical cell pads and three medial cell pads in D. goiasensis, but only two apical and one medial cell pad in D. riograndensis n. sp.Branch 2D in D. goiasensis has a single row of large spines on the medial surface of sub-branch I and sub-branch III has two basal spines opposite each other, with two apical and one subapical spine, whereas D. riograndensis n. sp. has the distal portion of sub-branch I covered in small spines, the medial surface spine row is composed of numerous small spinules, and sub-branch III has the two proximal spines next to each other and the posterior surface has a row of spines.Branch 2A has two cell pads and the proximal spine is arcuate and curved 90° in D. goiasensis, but there are no cell pads and the spine is straight and triangular in D. riograndensis n. sp.
The second antenna proximal antennomere of D. goiasensis lacks the posteriomedial projection that is so prominent in D. riograndensis n. sp.Finally, in D. goiasensis endopod I and II both are rectangular with a prominent lateral, multiramal projection, the distolateral corner bears a row of short, conical spines, and the distal margin is straight.In D. riograndensis n. sp.endopod I has the lateral projection is shaped like a long hook, the distolateral corner is produced, subquadrate, margined with long spines, the distal margin is sinuate, and the distomedial corner is triangular and acute, whereas endopod II is subquadrate and lacks setae or spines.No diagnostic characteristics were present in the female.
Six Dendrocephalus species have been previously reported from Brazil: D. brasiliensis, D. orientalis, D. goiasensis, Dendrocephalus thieryi Rabet, 2006, D. carajaensis, and an undescribed species (Rabet and Thiéry, 1996;Rabet, 2006;Chaves et al., 2011;Rogers et al., 2012).Our new species increases that number to seven, and is the southernmost record of the genus in Brazil.Rabet and Thiéry (1996), Rabet (2006), Chaves et al. (2011) each provided a key to the Dendrocephalus species for Brazil.Substitution couplets were provided by Rogers et al. (2012) to accommodate D. carajaensis.However, in order to facilitate identification of Dendrocephalus sensu stricto species, we present a key to all currently known species in the subgenus.

Key to the Dendrocephalus (Dendrocephalus) species
This key is based on males.This key does not include the undescribed species in Chaves et al. (2011).This key is only useful for mature males, which can be identified as being slightly larger than those females with mature eggs in the brood pouch.aCKnowleDgeMenTs Thanks to Ândrio Gonçalves and Luis Esteban Lanés for assisting in the collections.The field work was funded by Fundação Grupo Boticário de Proteção à Natureza.We are very grateful to Aloisio "Grilo" Ferreira for assisting and facilitating our communication.