Macrobrachium spelaeus, Cai & Vidthayanon, 2016

Cai, Yixiong & Vidthayanon, Chavalit, 2016, Macrobrachium spelaeus, a new species of stygobitic freshwater prawn from Thailand (Decapoda: Palaemonidae), Raffles Bulletin of Zoology 64, pp. 117-122 : 117-121

Macrobrachium spelaeus , new species

( Figs. 1–3 )

Material examined. Holotype: male, cl 13.7 mm, ( NIFI SH 00176 ), Tham Phra Wangdaeng , Baan Chompu southwest of Thung Salaeng Luang National Park, Pitsanulok Province, lower north Thailand, 100 m. from the cave entrance: 16.8379°N 100.877°E, 28 August 2002, coll. C. Vidthayanon. Paratypes: 1 male, cl 11.7mm ( OUMNH. ZC.2016-01-022) , 1 female, cl 11.9mm ( ZRC 2016.0049 ), same locality as holotype .

Etymology. The new species is named spelaeus (L., cavedwelling), after its stygobitic habit.

Remarks. Mcrobrachium spelaeus , new species, represents the first stygobitic Macrobrachium species found in Thailand. With the existence of the tufts of velvety setae on the dactylus of second pereiopods, short carpus in second pereiopods, relatively short rostrum which does not exceed the end of the scaphocerite, Macrobrachium spelaeus , new species, should be referred to the Macrobrachium pilimanus species group (cf. Cai et al., 2004). To date, there are 15 species recognised in the Macrobrachium pilimanus group, namely M. pilimanus ( De Man, 1879) , M. leptodactylus ( De Man, 1892) , M. hirsutimanus ( Tiwari, 1952) , M. dienbienphuense Dang & Nguyen, 1972 , M. poeti Holthuis, 1984 , M. eriocheirum Dai, 1984 , M. ahkowi Chong & Khoo, 1987 [= M. johnsoni Chong & Khoo, 1987 ], M. gua Chong, 1989 , M. forcipatum Ng, 1995 , M. platycheles Ou & Yeo, 1995 , M. pilosum Cai & Dai, 1999 , M. amplimanus Cai & Dai, 1999 , M. sirindhorn Naiyanetr, 2001 , M. kelianense Wowor & Short, 2007 , and M. empulipke Wowor, 2010 . With its reduced eyes, M. spelaeus could be easily separated by all the other members of the M. pilimanus group except M. poeti . Macrobrachium poeti was described from several caves in Gunung Sewu, Java, Indonesia. Macrobrachium spelaeus could be distinguished from M. poeti (cf. Holthuis, 1984) by having more teeth on the lower margin of the rostrum (2 or 3 vs. 1 in M. poeti ); the shorter merus of the second pereiopods (as long as palm vs. distinctly longer than palm in M. poeti ); the larger number of teeth on the cutting edges of the fingers (15 vs. several in M. poeti ), the slender propodus in third pereiopods (3.4 times as long as dactylus vs.3 times in M. poeti ). Compared to epigean species of the group, M. spelaeus morphologically resembles M. dienbienphuense Dang & Nguyen, 1972 , a species originally described from northern Vietnam, but also reported from China, Laos, and Thailand ( Cai et al., 2004; Hanamura et al., 2011), especially when taking into account of the form of second pereiopods. Besides the eyes, M. spelaeus could be separated from M. dienbienphuense (cf. Dang & Nguyen, 1972; Cai et al. 2004, Hanamura et al. 2011) by the form of rostrum (straight vs. convex); shorter major second pereiopods in male specimens (as long as body length vs. distinctly longer in M. dienbienphuense ) less setae/pubescence in second pereiopods (see fig. 3 vs. fig. 3 in Dang & Nguyen 1972); fewer number of teeth on the cutting edges of the fingers (15 vs. 18–32 in M. dienbienphuense ).

Comparative specimens examined. Macrobrachium dienbienphuense : 10 males, cl 9.0–11.0 mm, 5 ovigerous females, cl 6.7–8.3 mm, eggs 1.3 × 1.0 mm ( ZRC 2000.2693 ), Central Thailand, Lop Buri Province, Chai Badan , coll. Y. Cai, 20 June 1998 ; 9 males, cl 10.2–11.7 mm, North-east Thailand, Phibun, Mangsahan, Ubon Rachathani Mae Nam Moon, Mangsahan afternoon market, coll. Y. Cai et al., 16 June 1998 .

Figures

Fig. 1. Macrobrachium spelaeus, new species. A, B, cephalothorax; C, scaphocerite; D, antennal spine; E, epistome; F, fourth thoracic sternite; G, eighth thoracic sternum; H, 1st–3rd abdominal sterna with transverse ridge and median tooth; I, preanal carina; J, telson; K, uropodal diaeresis. Scale bars = 4 mm [A–C]; 1.5 mm [D]; 0.8 mm [E, H, I]; 1.2 mm [G, J]; 1.0 mm [F]; 0.5 mm [K] (holotype: male, cl 13.7 mm, NIFI SH 00176).

Fig. 2. Macrobrachium spelaeus, new species. A, first pereiopods; B, C, second pereiopods; D, E, third pereiopods, Scale bars = 2 mm [A, C]; 4 mm [B]; 1.5 mm [D]; 0.5 mm [E] (holotype: male, cl 13.7 mm, NIFI SH 00176).

Fig. 3. Colour photograph of Macrobrachium spelaeus, new species (paratype, male, cl 11.7mm, OUMNH.ZC.2016-01-022)