Macrobrachium sbordonii, Mejía-Ortíz, Luis M., Baldari, Fabiola & López-Mejía, Marilú, 2008

Mejía-Ortíz, Luis M., Baldari, Fabiola & López-Mejía, Marilú, 2008, Macrobrachium sbordonii (Decapoda: Palaemonidae), a new stygobitic species of freshwater prawn from Chiapas Mexico, Zootaxa 1814, pp. 49-57 : 50-54

Macrobrachium sbordonii new species

figs. 2–4

Holotype. Male, Carapace length (CL) = 18.2 mm, May 1988; R. De Cristofaro, E. Franco and C. De Monte coll.; terminal lake in the Sistema de la Lucha, Chiapas, Mexico (17° 03’ 40” N 93° 53’ 23” W); CNCR 25050 Allotype.- Female, CL= 17.5 mm, 21 April 1987; E. Franco, R. De Cristofaro coll., same locality as holotype; CNCR 25051.

Paratypes. 1 male, CL= 18.7 mm 3 females, CL= 20–21,5 mm; May 1988; R. De Cristofaro, E. Franco and C. De Monte, coll.; CNCR 25052. 1 male CL= 17.9 mm, 3 females, CL= 17.8–19.3 mm; 21 April 1987; E. Franco, R. De Cristofaro coll.; BC-UQROO-160. 2 males CL= 16–19.5 mm, 12 females CL= 14.7–22 mm; 10 April 1986; C. Giudici, M. Diana coll. (DB-Tor Vergata). All paratypes were collected in the type locality.

Description. Medium sized prawn, maximum total length 39.3 mm. Rostrum short, curved anteriorly, tip not reaching the distal border of scaphocerite but surpassing the third article of antennular peduncle; dorsal margin bearing 7 teeth, 1 in postorbital position, two teeth on ventral margin (fig. 2). Live M. sbordonii new species is white, without pigment in the body.

Carapace smooth, maximum length 17 mm, with antennal spine smaller than hepatic spine. Branchiostegal groove shallow.

Abdomen smooth, pleura of first three somites broadly rounded (fig. 2). Posteroventral margin of fourth and fifth pleura acute, all pleura bearing setae on ventral border. Sixth somite 1.3 times as long as fifth. Telson 1.2 times longer than sixth somite, shorter than uropodal rami; bearing two pairs of dorsal spines, first pair in distal fifth, second pair in middle section of telson; posterior margin broadly triangular bearing two pairs of lateral spines, inner pair 5 times longer than external one, with plumose setae between inner spines ( Fig. 4 G).

Eyes reduced, cornea with a small apical black point, this point bearing facets.

Antennules with acute stylocerite reaching proximal third of first peduncular segment (fig. 3C). First antennular segment with acute distolateral spine and concave depression to fit eye. Second antennular segment cylindrical, with sinuous distal margin and lateral row of long setae.

Antennae with basicerite bearing large spine on internal margin. Scaphocerite 2.4 times as long as wide, distolateral spine short, widely separated from distal margin of main blade (fig. 3A).

Mandibles with 3-segmented palp, first segment the shortest, second and third segments of equal length; incisor process with 3 conical teeth, molar process with 5 wide, rounded teeth on mesial border (fig. 4A).

Maxillules with bilobed palp, distal lobe slender, with three setae on the tip, proximal lobe blunt with three thick setae; anterior lacinia approximately oval, with three long setae on mesial margin, distal margin with five thick spines and a row of fine setae, lateral margin straight, with few setae; posterior lacinia tapering distally, curved inwards, distal half covered with setae (fig. 4B).

Maxillae with scaphognathite bordered with plumose setae, anterior lobe narrower and longer than posterior one; palp lack of setae, tapering distally, strongly curved inwards; endite bilobed, divided by incision along distal third, both lobes with tuft of setae on the tip (fig. 4C).

First maxilliped with bilobed endite, bearing marginal and submarginal setae along margin, and row of setae on surface of distal lobe. Exopod slender, 6 times as long as palp, distal third bearing long setae; palp simple, with two thick setae, shorter than endite; caridean lobe large, fused to base of exopod, bearing long, plumose setae all along margin; epipodite trapezoidal (fig. 4D).

Second maxilliped subpediform, podobranch present, well developed; endopodite 4-segmented, distal 2 segments oriented mesially, gnathal border with marginal setae and spines and submarginal setae; exopodite slender, almost twice as long as endopodite, tip bearing long, plumose setae (fig. 4E).

Third maxilliped pediform, slender, reaching beyond basal portion of antennal flagellum; arthrobranch present, well developed; coxa with rounded lateral projection (fig. 4F). Endopodite 3-segmented, with abundant setae, becoming denser distally; first segment slender, 1.3 times as long as second segment; second segment 1.3 times as long as third, distal margin ending in nail. Exopodite slender, flat, as short as first segment of endopodite, bearing long setae distally.

First pereiopods slender, smooth, with scarcity tufts of setae on both fingers. Tip of fingers surpassing distal margin of scaphocerite; palm slightly compressed, as long as dactylus; carpus 4.5 times palm length, 1.12 times merus length (fig. 3D).

Second pair of pereiopods slightly equal in size, without spines. Palm cylindrical, 3 times as long as wide, with disperse tufts of setae, 0.75 times dactylus length; carpus 2 times palm length, 1.09 times as long as merus; ischium 0.72 times merus length. Fingers not gaping, elongate, cutting margins covered with tufts of setae, fixed finger and dactylus without teeth (fig. 3E).

Propodus and dactylus of third pereiopod with several tufts of short setae. One row of three tufts of setae on inner border of propodus, distal pair of tufts of setae on articulation with dactylus and two rows of 7 and 9 movible spines on inner margin of propodus 1 pairs distally in articulation with dactylus. Propodus 2.5 times length of dactylus, 2 times carpus length (fig. 3F).

Fourth pereiopods, sparsely pilose; propodus 3 times dactylus length, 1.85 times as long as carpus; with one row of three movable spines on inner border of propodus, one pair of spines and tufts of setae on propodus–dactylus articulation (fig. 3G).

Fifth pair of pereiopods the longest. Propodus and carpus pilose; one longitudinal row of 4 movable spines, 1 spine on propodus–dactylus articulation; propodus 4 times dactylus length, 1.6 times carpus length (fig. 3H).

Appendix masculina 1.7 times length of appendix interna, inner margin with 12 pairs of spines (fig. 3B).

Etymology. The specific name is given in honor of Professor Valerio Sbordoni, Tor Vergata University of Roma Italy, an indefatigable biospeleologist providing an outstanding contribution to the knowledge of the cave fauna of Chiapas.

Habitat. This species lives in the Cueva de La Lucha, a cave system situated at the northeastern edge of the Selva del Mercadito, a large limestone area at the border region of Chiapas and Oaxaca in the southern Mexico. The cave, explored and visited in the course of various expeditions led by Professor V. Sbordoni, is described by Gambari & Topani (1986). The whole cave system is about 1300 m long, interrupted after 650 m by a large doline (sotano), 220 metres deep. A subterranean river flows into a large lake in the terminal cave section, where the new species lives. This lake has a deepest part of 5 m, with a maximum diameter of 140 m. The water temperature measured at the time of collection was 19° C (Sbordoni et al., 1987). The cave river is subjected to impressive flooding during the wet season.

A rich cave fauna inhabits this cave (Sbordoni et al., 1986, 1987; Sbordoni & Lucarelli, 1989 -90). Other notable aquatic taxa include a freshwater crab, a new species of troglomorphic crayfish of the genus Procambarus (description in process), and the stygobitic fish Rhamdia laluchensis Weber, Allegrucci & Sbordoni, 2003 .

Figures

FIGURE 4. Macrobrachium sbordonii new species, male holotype CNCR 25050. A, right mandible; B, right maxillule; C, right maxilla; D, first maxilliped; E, second maxilliped; F, third maxilliped; G, telson and uropods. Scale bars represent: A – E, 2 mm; F – G, 5 mm.