A new species of Kingsleya (Crustacea: Decapoda: Pseudothelphusidae) from the Xingu River and range extension for Kingsleya junki, freshwater crabs from the southern Amazon basin

Kingsleya castrensis sp. nov., a pseudothelphusid crab is described and illustrated from the Xingu River, state of Pará, southern Amazon region, Brazil. The new species is characterized by the male first gonopod bearing a large, well-developed apical plate, with a broadly rounded, thick distal lobe. New records of Kingsleya junki Magalhães, 2003 extend the distribution of this species eastward to the Tocantins River basin, in the state of Pará, Brazil.


MATERIAL AND METHODS
Specimens are deposited at the Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil (INPA), Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro (MNRJ), Museu Paraense Emilio Goeldi, Belém, Brazil (MPEG), Museu de Zoologia, Universidade de São Paulo, São Paulo, Brazil (MZUSP), and Senckenberg Research Institute and Natural History Museum (SMF). The following abbreviations are used: carapace width (cw), measured across the carapace at its widest point; carapace length (cl), measured along the midline, from the frontal to the posterior margin; carapace height (ch), the maximum height of the cephalothorax, measured as the distance between the dorsal and ventral edges of the shell; frontal width (fw), the width of the front measured along its upper border; male first (G1) and second (G2) gonopods; third maxilliped (Mxp3); cheliped (P1); pereiopods 2 to 5 (P2-P5); and sternal sulcus (s). Geographic coordinates inserted between brackets were taken from Google Earth. Illustrations were made using a Leica M8 stereomicroscope with a camera lucida; the computerized photographs were taken using a stereomicroscope Zeiss Discovery V12 (Automontage ® system). Measurements of carapace width and carapace length, in millimeters, were made with a calipers and are given in parentheses after the number of specimens examined. Terminology for describing the morphology of the G1 was adapted from SMALLEY (1964) and MAGALHÃES & TÜRKAY (2008).
Description. Carapace outline ellipsoid, widest medially (cb/cl 1.68); dorsal surface smooth, slightly convex, regions partially defined (Fig. 7). Two distinct gastric pits, close to each other, on metagastric region. Cervical grooves deep, narrow, nearly straight, faint proximally, distal end failing to reach anterolateral margin. Postfrontal lobules small, quite distinct; median groove indistinct. Surface of carapace between front and postfrontal lobules smooth and slightly inclined anteriorly and medially. Upper border of front smooth, angulate, slightly convex in dorsal view, median notch absent; lower border carinate, slightly sinuous in both frontal and dorsal view, more projected anteriorly than upper one, except medially. Upper orbital margin smooth, lower orbital margin slightly crenualte; exorbital angle low, obtuse (Fig. 13). Anterolateral margin of carapace nearly smooth, with very shallow depression just behind exorbital angle, followed by a set of faint, minute teeth increasing in size from the anterior to posterior portion; posterolateral margin smooth, barely defined. Epistome narrow; epistomial tooth triangular, deflexed, with carinate, smooth borders. Suborbital and subhepatic regions of carapace sidewall smooth; pterygostomial regions with narrow pilose patches along outer borders of bucal cavity (Figs. 8 and 13).
Endopod of Mxp3 with outer margin of ischium slightly convex, inner margin straight; outer margin of merus rounded, inner surface of palp covered with large setae; exopod of Mxp3 short, narrow, 0.18 times length of outer margin of ischium (Fig. 14). Aperture of efferent branchial channel wide, upper margin subquadrate, lacking setae (Fig. 13).
G1 (Figs. 1-4 and 9-12) sinuous, broadened distally, with strong median curvature on caudal surface in mesial view, bearing well-developed mesial process. Marginal suture sinuous, displaced to mesial side in distally, bearing several setae proximally. Lateral suture deep, extending 2/3 of gonopod length from proximal portion. Marginal process short, broad, subrectangular in mesial view, not projecting distally beyond field of apical spines area, distal notch in latero-caudal surface. Mesial process well developed, roughly subretangular, approximately 1.8 times longer than apical plate in mesial view, proximal portion rounded, distal portion produced into sharp conical spine pointing in mesial direction; mesial process juxtaposed to the apical plate, both structures clearly separated by a deep incision. Apical plate well developed, large, thick, expanded along caudo-cephalic axis, with 2 juxtaposed lobes; proximal lobe subtriangular, well developed, situated subdistally on mesio-caudal side, narrower than distal lobe, distal margin straight, stretching diagonally over the distal lobe, gradually merging to mesiodistal portion of the apical plate; distal lobe enlarged, caudal margin rather angulate in mesial view, distal margin slightly concave, mesial margin rounded. Apical spine field well developed, curved, narrow patch of minute spines, longitudinally directed along caudal side of apical plate, delimited by mesial, lateral borders of apical plate, distally opened by distinct notch at apex of apical plates proximal lobe. Sperm channel opening proximally at base of apical spine field.     Type locality and distribution. Brazil, state of Pará, city of Altamira. Most specimens were collected within the camp area of the "51° Batalhão de Infantaria de Selva" (B.I.S.), a unit of the Brazilian Armys Battalion of Jungle Infantry, headquartered in the city of Altamira. Additional specimens were also collected in in Altamira and Brasil Novo cities.
Ecological notes. Most of the crabs were collected on the margins of a 1-3m wide, third order tributary stream of the Xingu river. The stream is located inside a secondary forest fragment dominated by palm trees: Euterpe oleracea Mart. and Attalea phalerata Mart. ex Spreng in the flooded area, and Astrocaryum gynacanthum Mart. and A. aculeatum G. Mey in the well-drained soil area (terra firme). A floodplain along the borders of the stream varies from a few meters wide to almost a hundred meters according to topography and season (SALM et al. 2015). Adult crabs dig holes in the mud or hide between the aerial roots of the palm trees. Occasionally adult male and female crabs were found together in the same hole. Juvenile crabs were found on palm leaves and trunks or beneath leaf litter. A few specimens were collected outside the flooded margins of the stream, in the terra firme area.
Female crabs carried young crabs under their abdominal brood pouch. Morning field investigations revealed that 68.5% of the 108 observed crabs were males. The species is probably aggressive and territorial, since one of the chelipeds was lacking in 20% of the males and 13% of the females. The loss of chelipeds may also be attributed to autotomy as a response to predators, since skeletal remains and pereiopods of Kingsleya were frequently found in the studied area.
Etymology. The specific epithet refers to castra, the Latin word for military camp, in reference to the Brazilian Army battalion camp where this species was found.
Remarks. The new species is attributed to Kingsleya since its G1 shows the diagnostic characters of the genus, namely the marginal process distally enlarged, not overreaching the apical field of spines, the bi-lobed apical plate, the mesial process clearly separated from the apical plate and standing out from the cephalic surface of the stem; the apical plate with two partially superimposed lobes; and the field of apical spines distally divided by a terminal notch (MAGALHÃES & TÜRKAY 2008).
Kingsleya castrensis sp. nov. can be easily distinguished from K. junki Magalhães, 2003 andK. ytupora Magalhães, 1986, the other two species of the genus that occur in the Xingu River (MAGALHÃES 2003b) by characters of the G1s apical plate. In both K. junki and K. ytupora (see MAGALHÃES 2003b: 384, figs. 1B-D, and 385, fig. 2B, respectively) the apical plate is narrow and produced distally in relation to the mesial process, whereas the apical plate of K. castrensis sp. nov. is distinctly enlarged and short in relation to the mesial process (Figs. 1, 3, 5 and 6). Moreover, in K. castrensis sp. nov. the mesial margin of the apical plates distal lobe is smooth (Fig. 1), whereas in K. junki the distal plate is clearly indented (Figs. 5 and 6). The distal margin of the apical plate, in mesial view, is rounded and rather narrow in K. ytupora (see MAGALHÃES 2003: 385, fig. 2B), whereas in K. castrensis sp. nov. this margin is much broader rounded and enlarged (Figs. 1, 3 and 4). Another character that readily separates these two species is the presence (in K. ytupora) or absence (in K. castrensis sp. nov.) of a set of six to seven large, sharp teeth on the anterolateral margin of the carapace; in the latter species, this margin is fringed with a set of faint, minute teeth that lends to this margin an almost smooth appearance.
Kingsleya castrensis sp. nov. is unique among the species of the genus because of the distinctly enlarged, broadly rounded apical plate of its G1. All other species of Kingsleya have a G1 with an apical plate that is, in spite of their specific differences, much narrower, tapering and roughly subtriangular in shape (MAGALHÃES 1986, 1990, 2003b, 2005, MAGALHÃES & TÜRKAY 2008 Distribution. The species was known only from its type locality, Vitória do Xingu, downstream from Altamira, on the left bank of Xingu River (MAGALHÃES 2003b). The present record from Jacundá extends its distribution to the eastern Amazon region, in the middle course of the Tocantins River basin.
Ecological notes. The specimens of K. junki were found in the vegetated margins of the Leonardo da Vinci stream, a small, clear-water tributary on the left bank of the Xingu River. All of the crabs were collected inside holes or beneath rocks. Two couples were found, and males and females apparently shared the same hole.
Remarks. The G1 of the specimens reported herein (Figs. 5 and 6) is similar to that of the holotype of K. junki (see MAGALHÃES 2003b: 384, fig. 1B), although some variability can be noticed in the morphology of the apical plate, particularly in the mesial margin of the distal lobe. In the holotype, this margin is indented both proximally and distally, whereas it is more distinctly indented only in the proximal portion of this margin in the present specimens. Since such a situation can be verified in the specimens from both the Xingu River and Tocantins River basins, this might be due to intraspecific variability and, therefore, the specimen from Tocantins River was considered to be conspecific with those from the Xingu River basin.