Macrobrachium prabhakarani, Pillai & Unnikrishnan, 2012

Pillai, P. M. & Unnikrishnan, V., 2012, A new species of Macrobrachium (Decapoda, Palaemonidae) from Vamanapuram River, Southern Kerala, India, Zootaxa 3528, pp. 63-68 : 64-68

Macrobrachium prabhakarani sp. nov.

( Figs. 1–2 )

Material examined. HOLOTYPE: 1 male (no. 1, table 1) (ZSI/WGRS/IR/INV 2156), collected from the middle reaches of the Vamanapuram River , (76° 53ʹ 54.00ʹ E, 8° 43ʹ 23.81ʹ N) Kerala, South India, 6 June 2006 . Paratypes: 1 male (no. 2, table 1) (ZSI/WGRS/IR/INV 2157), 3 males and 2 females (1 ovigerous), (nos. 3–7, Natural History Museum of the Dept. of Zoology , Mahatma Gandhi College, Thiruvananthapuram (Reg. no. MGC/ TVM/NHM-INV/1/2012).

Measurement of holotype in mm: total length, 42; carapace length, 13; length of rostrum, 7; length of telson, 5; first chelate leg: ischium (i) 2.0; merus (m) 5.0; carpus (c) 6.0; propodus (p) 2.8; dactyl (d) 1.4; right second chelate leg (large): i = 6.0, m = 7.0, c = 6.0, p = 13.0, d = 7.0; left second chelate leg (small): i = 4.5, m = 5, c = 5, p = 10, d =6

First non-chelate leg (pereiopod 3): i = 2.5, m = 5.0, c = 2.5, p = 5.0, d = 2.0

Second non-chelate leg (pereiopod 4): i = 2.5, m = 5.0, c = 2.5, p = 5.0, d = 2.0

Third non-chelate leg (pereiopod 5): i = 2.5, m = 5.5, c = 3.0, p = 6.0, d = 2.0

Diagnosis. Rostral formula 12–14/1–2, 5–7 postorbital teeth; carapace smooth, distal rostrum directed forwards and palm equal to fingers in first chelate leg. Larger second chelate leg with 9 denticles, on proximal cutting edge of movable finger, fourth denticle larger than others. 6 denticles in immovable finger, first and sixth denticles larger. Numerous setae throughout the fingers, compared to podomeres.

Description (holotype). Rostrum moderately long, upper margin straight, exceeds distal end of antennular peduncle, tip directed forwards. Dorsal margin of rostrum with 12–14 teeth, 5–7 postorbital (table 1); ventral margin with 2 teeth, rarely1. Small setae present between dorsal and ventral teeth.

Carapace smooth (length, 7.0 mm–13.0 mm), antennal and hepatic spines present; the latter situated just below and behind the level of the former (figs. 1A, 2). Abdomen glabrous, pleurae of somites I–III typical, pleura IV–V directed backward, pleura VI ending in a spine. Telson conical with 2 pairs of spines on dorsal surface, first pair situated midway, distal pair a little behind, at about 0.75 of telson length. Posterior end of telson with 2 pairs of spines, outer pair smaller and immovable, inner pair longer and movable, overreaching tip of telson. A few plumose setae present between inner pair of movable spines (fig. 1F). Antennules typical in structure, outer lateral spine of antennal scale, sharp and pointed forwards.

First pereiopod slender, tips of chelae over reaching antennal scale, when extended. Ischium shorter than propodus and merus, carpus longest podomere, merus longer than propodus, dactylus shortest. Palm equal to fingers (fig 1B).

Large second pereiopod (length range, 25.5 mm –32.0 mm), strong and unequal, 0.62 to 0.76 times total body length, in different specimens. Merus longer than carpus and ischium, propodus longest podomere. Carpus and ischium equal in length and they are the shortest podomeres. Merus and dactylus equal in length. Nine denticles present on proximal cutting edge of movable finger, fourth denticle larger than others. Immovable finger with 6 denticles, first and sixth larger than others. Two tufts of stiff setae present on distal part of each finger. Numerous setae present throughout the fingers, when compared to other podomeres (fig 1C).

Non-chelate legs (fig 1E), and all pleopods normal structure as of the genus. Spinous setae present at inner margin of appendix masculina.

Remarks. The present specimens share certain characters with Macrobrachium scabriculum ( Heller, 1862) and certain other characters with M. madhusoodani Unnikrishnan et al. 2011 . The number of dorsal rostral teeth, post orbital teeth and ventral teeth in certain specimens of M. prabhakarani sp. nov. is within the range of M. scabriculum and M. madhusoodani . Rostrum moderately long and tip directed forwards, both in M. prabhakarani sp. nov. and M. madhusoodani . In first pereiopod of all three species, ischium shorter than merus, and carpus more than twice the length of chela. Second pereiopod of all three species, strongly unequal, and in the larger second pereiopod, ischium shorter than merus. But M. prabhakarani has distinct differences with these two species in diagnostic characters (table 2).

In M. scabriculum rostrum is very short, extending only to tip of antennular peduncle, upper margin convex, distal end pointing downwards. In M. madhusoodani rostrum is moderately long, but not reaching the distal end of the antennal scale, basal crest not much raised and distal end directed forwards (Unnikrishnan et al. 2010). But in M. prabhakarani sp. nov., rostrum moderately long, upper margin straight and tip of rostrum reaches the distal end margin of antennular peduncle and directed forwards.

In M. scabriculum number of dorsal rostral teeth ranges from 12–15 and in M. madhusoodani 10–14, though in M. prabhakarani the range is 12–14, the species differs from M. scabriculum in important taxonomic characters like moderately long rostrum with straight upper margin and forwardly directed tip. In M. scabriculum , number of dorsal rostral post orbital teeth is 5, where as in M. madhusoodani 5–6 (rostral teeth evenly distributed in smaller specimens, though the proximal 3 teeth are distantly placed in larger specimens). But in M. prabhakarani 5–7 post orbital teeth are present.

In M. scabriculum no. of ventral rostral teeth ranges from 1–3 usually 2 and in M. madhusoodani 2, rarely 3. But in M. prabhakarani 1–2 ventral rostral teeth are present. In M. scabriculum carapace is scabrous with minute spinules, but in M. prabhakarani carapace is smooth like that of M. madhusoodani .

In the first pereiopod of M. prabhakarani sp. nov. ischium less than half the length of merus whereas in M. scabriculum , ischium inflated and slightly shorter than merus. In M. madhusoodani , ischium shorter than merus; but merus shorter than carpus in all the three species. In M. prabhakarani sp. nov., carpus more than twice the length of chela. This is similar to the situation in M. scabriculum and in M. madhusoodani . In M. prabhakarani sp. nov., palm equal to fingers like that of M. scabriculum , whereas in M. madhusoodani palm longer than fingers.

In all the three species second pereiopod strongly unequal, right or left longer. In the larger second pereiopod of M. prabhakarani sp. nov., ischium shorter than merus, merus longer than carpus and carpus equal to palm. In M. scabriculum , ischium shorter than merus, and merus almost equal to carpus, carpus almost equal to palm or slightly longer. In M. madhusoodani ischium shorter than merus, merus almost equal to carpus and carpus slightly shorter than palm.

In M. prabhakarani sp. nov. fingers stout and numerous setae are present throughout the fingers, compared to the other parts of the pereiopod; nine denticles present on the proximal cutting edge of the movable finger, fourth denticle larger than the others; immovable finger with six denticles, first and sixth are larger than the others; two groups of stiff setae present on the distal part of each finger. In M. scabriculum , fingers slender and distinctly longer than palm, cutting edge of fingers with more than twenty denticles, entire palm and basal part of fingers covered with thick pubescence. In M. madhusoodani fingers are not much slender as in M. scabriculum , and proximal cutting edge of fingers with four denticles in the movable and three in the immovable finger.

In M. prabhakarani telson extends to the level of the outer lateral spine of the uropodal exopod (fig. 1D) as in M. scabriculum . But in M. madhusoodani telson extends beyond the level of outer lateral spine of uropodal exopod.

Etymology. The species name is in memory of T. K. Prabhakaran, Thalathil Leelalayam, Thrikkannapuram, Thiruvavanthapuram, Kerala, an ardent naturalist who whole heartedly assisted the authors in collecting the specimens and died on 21 st December 2006. The name thus is a noun in the genitive singular.

Figures

FIGURE 1. Macrobrachium prabhakarani sp. nov., specimen no. 1, holotype (male). A, carapace- left lateral view; B, 1st chelate leg, distal part; C, second large chela, enlarged; D, telson and uropod, lateral view; E, 3rd pereiopod, distal part; F, telson.

FIGURE 2. Macrobrachium prabhakarani sp. nov., specimen no. 2, paratype. Carapace in left lateral view.