Macrobrachium pantanalense, Santos, Antonina Dos, Hayd, Liliam & Anger, Klaus, 2013

Santos, Antonina Dos, Hayd, Liliam & Anger, Klaus, 2013, A new species of Macrobrachium Spence Bate, 1868 (Decapoda, Palaemonidae), M. pantanalense, from the Pantanal, Brazil, Zootaxa 3700 (4), pp. 534-546 : 535-541

Macrobrachium pantanalense sp. nov.

( Figs 1–5 )

Material examined. Male holotype: (5.2 mm CL, 30.5 mm TL, 7.1 mm rostrum) MZUSP 26207. 1 Ovigerous female paratype: (7.9 mm CL, 42.6 mm TL, 11.5 mm rostrum, 0.92± 0.08 mm eggs diameter). 2 female paratypes: (9.0 and 9.6 mm CL, 54.8 and 55.0 mm TL, 14.4 and 14.3 mm rostrum). 1 male paratype: (and 7.4 mm CL, and 43.0 mm TL, and 10.7 mm rostrum) MZUSP 26208, Baiazinha Lagoon (20º16’S / 56º23’ W), an adjacent shallow lake connected to the Miranda river and located in the Pantanal of Miranda, State of Mato Grosso do Sul (MS), Brazil, <1 m depth, coll. L. Hayd, October 2009.

Diagnosis. Small caridean shrimp with well developed, dorsally and ventrally toothed rostrum. Carapace presents antennal and hepatic spines and branchiostegal sulcus. Mandible with 3-segmented palp. All maxillipeds with exopods. First two pairs of pereiopods chelate, slender, as long as the carapace. Last three pairs of pereiopods simple. Telson with two pairs of dorsal and two pairs of posterior spines.

Description. Small sized palaemonid shrimp of subcylindrical form ( Figs 1 , 2 , 5 ). Carapace smooth, glabrous, hepatic and antennal spines present. Rostrum long with anterior half directed obliquely upwards, about 1.6 of the carapace length (1.2 for individuals with less than 35 mm long), with 9 to 11 teeth on dorsal margin, the first one placed on the orbit or slightly behind the orbit (smaller individuals); the last three teeth, one is placed between two distinct naked spaces, the last two near the tip ( Figs 1 , 2 ). However, some males have the teeth equally distributed along the dorsal margin ( Fig. 4 A). The ventral margin has 5 to 9 teeth ( Figs 1 , 2 , 4 A). Eye with globular cornea, about 0.2 times of carapace length ( Fig. 3 A).

Abdomen smooth. The sixth segment about 1.5 times length of the fifth, with the posterolateral and posteroventral angles strongly produced and acute. First four pleurae broadly rounded, the fifth produced posteriorly and acute ( Figs 1–2 ).

Telson about 1.2 times the sixth segment length and about 3 times longer than the proximal width, lateral margins are straight and convergent, ending in sharp median point ( Figs. 4 N–4P). The dorsal surface bears two pairs of spines, at about 0.5 and 0.7 of telson length. On the posterior margin presents two pairs of spines, the exterior pair distinctly smaller than the interior one, which overreaches the apex of the telson. In most of specimens, the inner pair of spines reaches farther beyond the tip of telson. All specimens present a pair of plumose setae placed between the apex of telson and the interior pair of spines. The plumose setae are longer than the spines ( Fig. 4 P).

Antennule ( Fig. 3 B): proximal peduncular segment about 1.8 times longer than wide, anterolateral margin strongly produced, with stout distolateral tooth extending to about 0.4 of intermediate peduncular segment length, stylocerite acute, short, reaching about 0.4 of the proximal segment length; intermediate peduncular segment about 0.3 of proximal segment length, with lamellae very obliquely articulated with distal segment; distal segment about 0.2 of proximal segment length; upper flagellum biramous with about 12 rami fused proximally.

Antenna ( Fig. 3 C): distal peduncular segment reaching about 0.3 of scaphocerite length; flagellum about 5 times carapace length; scaphocerite exceeds the antennular peduncle, about 3.5 times longer than wide, lateral margin strait, with stout distolateral tooth slightly exceeded by broad distal margin.

Mandible ( Fig. 3 D): robust incisor process with three teeth; mandibular palp slender with three segments, distal segment slightly longer than the two proximal segments, as figured. Maxillulla ( Fig. 3 E): palp bilobed, unarmed, as figured. Maxilla ( Fig. 3 F) with basal endite deeply bilobed; palp unarmed; scaphognathite well developed, lobes distally rounded, with about 183 setae along margins.

First maxilliped ( Fig. 3 G) with distinct basal and coxal endites, epipod bilobed (not figured), palp small with 2 simple setae, exopod with caridean lobe and flagellum with long plumose setae on the distal part. Second maxilliped ( Fig. 3 H) with stout endopod, terminal dactyl article, distally elongated, with rows of long marginal setae; propodus broader than long, with sparsely distributed setae along the upper margin; carpus short, with very small simple setae; merus longer than ischium; exopod two-segmented, proximolaterally with lamellar expansion, plumose setae on distal segment; epipod simple. Third maxilliped ( Fig. 3 I) with robust endopod, all three segments strongly setose, proximal segment with lamellar expansion; exopod not reaching distal margin of ischiomerus, with plumose setae on distal margin; coxa armed with a few setae on inner lateral margin; ventral arthrobranchs larger than dorsal ones.

First pereiopod ( Fig. 4 B) slender, slightly overreaching scaphocerite (in smaller specimens reaching scaphocerite), chela with palm slightly compressed, fingers about equal to palm length, with entire cutting edges along almost all finger length, carpus about 2.6 times chela length and 1.2 times merus length.

Second pereiopods ( Fig. 4 C) similar, equal, overreaching tip of rostrum; chela slender, palm about 8 times longer than wide, glabrous, fingers sparsely setose with tufts of setae on tip, fingers about 0.44 of palm length, with stout, feebly hooked tip, distal 0.7 with entire cutting edge, proximal edge with one small tooth; carpus slender, unarmed, about 1.7 times longer than chela; merus unarmed, about 0.6 of carpus length; ischium sparsely setose, about as long as merus; basis and coxa without special features.

Third to fifth pereiopods ( Figs 4 D–4F) similar, slender, not reach tip of scaphocerite; third pereiopod with feebly curved dactylus, dorsal with sparse packs of short setae, ventral border sharp, propodus about 2.2 times dactyl length, with 5 single ventral spines, 2 single spines placed dorso-distally and 1 pair placed distally, carpus about 0.44 of propod length, merus about 2.6 times carpus length; fourth pereiopod with dactyl feebly curved, dorsally with sparse setae, ventral border sharp, propodus about 2.9 times dactyl length, with 5 spines along ventral margin and 2 spines placed distally, carpus about 0.4 of propod length, with distal margin strongly produced; fifth pereiopod with feebly curved dactylus, with sparse simple small setae on both margins, propod about 3.5 times dactyl length, with small simple setae on dorso-distal margin, carpus about 0.44 of propod length, with distal margin strongly produced.

First pleopod ( Figs 4 G–4H) with basipodite 2.9 times longer than wide, endopod 0.4 of basipodite length, proximally wider than distally, with 13 fine plumose setae along the half distal margin, 9 very small simple setae placed sub-marginally. In males the endopod is 0.7 of basipodite length, slightly tapering distally, medial border centrally emarginated, with 33 long finely plumose setae along margin, proximally 9 longer, fine plumose setae, sub-marginally,5 small setae. Appendix interna absent in first pleopod but present on second to fifth pleopod. Appendix masculina ( Fig. 4 J) on second pleopod of males about 2/3 the size of the endopod and two times as long as appendix interna. Appendix masculina has one sparsely setose spine near the anterior end, 11 simple setae along margin, and a strong seta at posterior end. Third to fifth pleopods ( Fig. 4 K–4L) with endopod slightly smaller than exopod, all with plumose setae on margins, as figured.

Uropod ( Fig. 4 M) protopod with lateral small tooth; exopod with daeresis bearing very small tooth laterally; endopod subequal to exopod length.

Color in life. The animals are semi-transparent with small brownish patches all over the body, including appendices such as the pereiopods, the uropods, and the scaphocerite, which gives it an overall beige appearance ( Fig. 5 A).

Etymology. The new species is named after the region where it was spotted for the first time, the Pantanal (Portuguese name, meaning large wetland or swamp). This seasonally flooded savanna region is considered as the world’s largest wetland, being a UNESCO World Heritage Site since the year 2000.

Type locality and distribution. All specimens of Macrobrachium pantanalense were collected from the Baiazinha Lagoon, a shallow lake connected to the Miranda River in the Pantanal of the State of Mato Grosso do Sul, Brazil.

Habitat and ecology. The Rio Miranda is one of the major rivers of the Pantanal section in the state of Mato Grosso do Sul, Brazil. Shrimps are most commonly found in lentic habitats connected to the main river (e.g. Lagoa Baiazinha; see Hayd and Anger, 2013) as well as near the river banks, where currents are reduced and where fallen trees, overreaching riparian vegetation, or floating mats of aquatic plants ( Eichhornia azurea , E. crassipes , Alchornea castaneifolia ) provide shelter and some shade. Ecological and hydrological characteristics of the Rio Miranda have been described by Depaula et al. (1995), Resende et al. (2000), Hayd and Nakagaki (2002), Mendes et al. (2004), Resende et al. (2006), Pivari et al. (2008), Soares and Oliveira (2009); shallow Pantanal lakes, in general, were described in more detail by Heckman (1998), Willink et al. (2000), Suarez et al. (2004), Wantzen et al. (2008), and Tondato et al. (2010).

Figures

FIGURE 1. Macrobrachium pantanalense, sp. nov., male holotype, 5.66 mm CL, MZUSP 26207. Lateral view. Scale bar: 2.0 mm.

FIGURE 2. Macrobrachium pantanalense, sp. nov., ovigerous female paratype, 7.85 mm CL, MZUSP 26208. Lateral view. Scale bar: 2.0 mm.

FIGURE 3. Macrobrachium pantanalense, sp. nov.. A—rostrum and pereion of female paratype (9.0 mm CL), dorsal view, MZUSP 26208. Male holotype MZUSP 26207: B—antennule; C—antenna; D—mandible; E—maxilulla; F—maxilla; G—first maxilliped; H—second maxilliped; I—third maxilliped. Scale bars: 2.0 mm (A); 1.0 mm (B-I).

FIGURE 4. Macrobrachium pantanalense, sp. nov.. A—rostrum of male paratype (7.2 mm CL) MZUSP 26208. Male holotype MZUSP 26207: B—first pereiopod; C—second pereiopod; D—third pereiopod; E—fourth pereiopod; F—fifth pereiopod. G—first pleopod of female paratype (9.0 mm CL) MZUSP 26208. Male holotype MZUSP 26207: H—first pleopod of male; I—second pleopod of male; J—appendix interna and masculina of male; K—fourth pleopod of male; L—fifth pleopod of male; M—uropod. N—telson of female paratype (9.0 mm CL) MZUSP 26208. Male holotype MZUSP 26207: O—telson and uropods of male; P—posterior part of telson of male. Scale bars: 1.0 mm.

FIGURE 5. A—Live color pattern of Macrobrachium pantanalense, sp. nov.; top: ovigerous female; below: male. B—Live color pattern of M. amazonicum ovigerous female.