The genus Plesionika Spence Bate, 1888 has wide distribution all over the world and it is one of the most species rich genus in the family Pandalidae with 92 described species (De Grave and Fransen, 2011). The deep-sea habitat of Plesionika species makes their distribution more restricted than that of the pelagic shrimps, which contributes to speciation within the genus (Cardoso Irene, 2011). Eleven species of Plesionika are reported to occur in Indian waters (Rajool Shanis et al., 2012), most of them are rare in the fishery, except P. martia (A. Milne-Edwards, 1883)and the so called P. spinipes.In the deep-sea shrimp fishery of India, P. spinipes is one of the most dominant species (Rajan et al., 2001; Radhika., 2004; Rajool Shanis et al., 2012 ).The Plesionika narval (Fabricius, 1787) group consists of fourteen species including P. spinipes and the closely related P. grandis Doflein, 1902 and P. quasigrandis Chace, 1985(Chan and Crosnier, 1991).The P. narval group is characterized by the rostrum being very long and armed with numerous closely set teeth along almost the entire length of both dorsal and ventral sides. The species in this group are very similar morphologically, often causing misidentification. Chan and Crosnier (1991) and Fransen (2006) doubted the validity of Pandalus (Parapandalus) spinipes reported by Alcock (1901) from Kanyakumari and the taxonomic description of the species provided by George and Vedavyasa Rao (1966) from the southwest coast of India and suggested that the species in Indian waters may be P. grandis or P. quasigrandis. This report provides morphological characters for the three species in question to discuss the identity of P. spinipes in Indian waters.

1 Materials and Methods

Samples of Plesionika spp. were collected from deep-sea shrimp trawler landings at Kollam and Cochin fisheries harbour (Kerala), southwest coast of India, Arabian Sea and Tuticorin fisheries harbour (Tamilnadu), southeast of India, Bay of Bengal (Figure 1).Measurements were taken using a digital caliper to the nearest 0.01 mm and the total length (TL) measured from the tip of rostrum to tip of telson and carapace length (CL) from the orbital margin to the posterior dorsal edge of the carapace. The identification and description of species in the present study are in accordance to Chan and Crosnier (1991) and Chace (1985). Specimens examined in the present study are deposited in the collection of National Bureau of Fish Genetic Resources, Cochin Unit, Cochin, India (NBFGR CH) and Pelagic Fisheries Division in Central Marine Fisheries Research Institute (CMFRI, PFD), Cochin, Kerala, India.

 

Figure 1 Map of the location of the fisheries harbour where the specimens of Plesionika quasigrandis were collected.

 

Materials examined: Plesionika quasigrandis, NBFGR CH 1142, ovigerous female, CL 22.92 mm, CMFRI PFD CR 133-140, 8 specimens, 5 female, CL 17.2-24.8 mm (3 ovigerous and 2 non-ovigerous) 3 male, CL 18.9-23.2 mm, off Kollam, Kerala coast, India, Arabian Sea, 220-300 m depth, CMFRI PFD CR 141-146, 6 specimens, 4 female, CL 18.3-23.8 mm (3 ovigerous and 1 non-ovigerous) 2 male, CL l19.1-23.6 mm, off Tuticorin, Tamil Nadu coast, India, Bay of Bengal, 200-280 m depth.

2 Results and Discussion

The Plesionika narval group is generally considered to be a taxonomically complex species cluster. According to Chan and Crosnier (1991), P. spinipes, P. grandis and P. quasigrandis belongs to the P. spinipes subgroup within the P. narval group. The species in this subgroup possess the fourth abdominal pleuron pointed. These three species bear great morphological similarity and this led to doubts about the records of P. spinipes in India.

Table 1 Comparisons of morphological characters of Plesionika spinipes, P. grandis and P. quasigrandis.

Plesionika quasigrandis differs from P. spinipes in several important characters including morphometry, colour pattern and geographical distribution. The pattern and range of rostral teeth is different in the two species. In P. spinipes the range of rostral teeth on the ventral side is between 24-36 and the posterior ten ventral rostral teeth usually corresponds to more than thirteen dorsal teeth, while in P. quasigrandis these are 31-40 and eight or less, respectively. The dorsal and ventral rostral teeth count of P. quasigrandis in the present study differs from the description provided by Chace (1985), Chan and Crosnier (1991), Hanamura and Evans (1996) and Fransen (2006). A deep notch is present in the distal margin of the endopod of the first male pleopod of P. spinipes, which is absent in the same pleopod of P. quasigrandis. The important morphological differences among the P. spinipes, P. grandis and P. quasigrandis are given in the Table 1.

Figure 2 Plesionika quasigrandisChace, 1985, ovigerous female, off Kollam (Arabian Sea), India