Metapenaeopsis difficilis Crosnier, 1991

Padate, Vinay P., K. A., Mary Baby, Cubelio, Sherine Sonia, Saravanane, Narayanane & Sudhakar, Maruthadu, 2020, First records of dendrobranchiate prawns (Decapoda: Dendrobranchiata) from the Andaman Sea, India, Journal of Natural History 54 (7 - 8), pp. 405-418 : 408-410

Metapenaeopsis difficilis Crosnier, 1991

( Figures 2 , 3 )

Metapenaeopsis di ffi cilis Crosnier, 1991, p. 167 (key), p. 170 (key), p. 255, figs 65 – 67 – Crosnier 1994a, p. 340 –, Crosnier 1994b, p. 370 –, Crosnier 2007, p. 302 (list).

Material examined

1 ♀, Andaman Sea, FORVSS stn. 33402B, 10°42 ʹ 23 ” N, 93°13 ʹ 29 ” E, 124 m depth, CL (15.0 mm) ( IO /SS/DEN/00055) .

Geographic and bathymetric distributions

Western Pacific: 21 – 200 m depth from the Philippines, Indonesia, Coral Sea, New Caledonia, Marquesas Islands ( French Polynesia) ( Crosnier 1991), and 105 – 440 m depth off the Wallis and Futuna Islands ( Crosnier 1994 a, 1994b). Indian Ocean: 124 m depth in the Andaman Sea, India (present study).

Diagnosis

(modified from Crosnier 1991)

Rostrum short, reaching middle of second segment of antennule (CL:RL 1.00:0.53), distal end directed slightly upwards, dorsal margin with seven teeth, ventral margin nearly straight, edentulate, bearing long setae.

Carapace short (TL:CL 1.00:0.28), covered with short setae; epigastric tooth at anterior one-fourths of CL; antennal spine small; hepatic spine slightly larger, pterygostomian spine prominent; stridulating ridge absent ( Figure 2 (a)).

Eyes large, pigmentation prominent, eyestalk without tubercle on inner margin.

Inner antennular flagellum 0.5 times as long as peduncle, prosartema well developed. Antennal scaphocerite long, with prominent spine.

Maxillipeds II – III with long exopods.

All pereiopods with exopods and epipods; PI – III missing; PIV – V long (CL:TPLIV 1.00:1.20; CL:TPLV 1.00:1.47), dactyli shorter than propodi (PPLIV:PDLIV 1.00:0.50; PPLV:PDLV 1.00:0.40).

Abdomen long (TL:AL 1.00:0.43), covered with short setae, somites I – II rounded dorsally, somite III – VI not rounded, and with prominent broad, mid-dorsal carina, flattened dorsally, with split ends posteriorly; carina on somite 4 splitting widely with median deep notch ( Figure 2 (b)); somite VI long, (AL:somite VI length 1.00:0.27; somite V length:somite VI length 1.00:1.86). Uropodal exopod with disto-lateral spine.

Telson slender, reaching distal end of spine on uropodal exopod, with one pair of large sub-apical fixed spines and three pairs of movable spines laterally.

Thelycum with a low lobe between bases of PIII; thelycal plate between bases of PIV transversely oval, bearing minute median spine anteriorly, flanked by convex margins; intermediate zone comprising a median ramp flanked by a pair of apertures of seminal receptacles; transverse plate between bases of PV sinuous, with straight ends; posterior plate divided into one broad, low central lobe with median denticle, and two high lateral lobes ( Figure 2 (c)).

Remarks

Metapenaeopsis di ffi cilis is a small-sized species [CL 4.8 – 17.2 mm ( Crosnier 1991); CL 8.0 mm ( Crosnier 1994 a, 1994b); CL 15.0 mm (present study)], widely distributed in the Western Pacific region ( Crosnier 1991, 1994a) ( Figure 3 ). This species was described from a female specimen (MNHN-Na 12577) collected from depths of 92 – 95 m in the Sibuyan Sea, Philippines, during the MUSORSTOM 3 expedition ( Crosnier 1991). The present observation is the first record from Indian waters, indicating westward extension of its geographical range ( Figure 3 ).

This species is defined by a combination of the following morphological characters (following Crosnier 1991): rostrum bearing 7 or 8 dorsal teeth, except epigastric tooth; outgrowth on the sternum, between PIII, low, unarmed; thelycal plate anterior margin slightly convex; petasma with left valve lacking terminal tip, distoventral element reduced, spiral element with distal part of last turn with wing bearing large rib ventrally; left distodorsal element of petasma with quadrangular distal portion visible in ventral view, distal lobule well developed, slightly curved dorsally; thoracic somite VII completely lacking, or bearing weakly developed posterior-thoracic arthrobranch, lower arthrobranch rudimentary, pleurobranch variable. The present confirmation of the species was on the basis of morphological characters (thelycum and accessory structures), and herein agrees with the original description and illustrations of the holotype female of M. di ffi cilis (voucher number MNHN-Na 12577) as emphasised by Crosnier (1991, p. 255, figs 65 – 66). The specimen is characterised by an upper rostrum with 6 teeth [vs 8 dorsal teeth in the holotype ( Crosnier 1991, fig. 65a)], third pleonal somite with flattened middorsal carina having split wider posteriorly (vs third pleonal somite with mid-dorsal carina slightly split posteriorly in the holotype ( Crosnier 1991, fig. 65b – c), and an oval-shaped thelycal plate with convex margins flanked by a pair of wide apertures of the seminal receptacle (vs thelycal plate flanked by a pair of small apertures of the seminal receptacle in the holotype ( Crosnier 1991, fig. 66).

The present specimen also shows affinity with M. quinquedentata ( De Man, 1907) in the number of dorsal rostral teeth, and the presence of a wide notch separating the split ends of the dorsal carina on pleonal somite III ( Crosnier 1991).

Metapenaeopsis di ffi cilis is very similar to M. quinquedentata ( De Man, 1907) in the posterior splitting of the dorsal carina of the third pleonal somite with a notch separating the split ends, and the presence of a protuberance on the sternum between the bases of pereopods III. However, M. di ffi cilis differs from M. quinquedentata in having 8 rostral teeth [vs 6 rostral teeth in M. quinquedentata ( Crosnier 1991, fig. 62a)]. Secondly, M. di ffi cilis lacks a well-developed outgrowth on the sternum between the third pair of pereopods (vs the presence of a well-developed outgrowth, with an apical spine, on the sternum between the third pair of pereopods in M. quinquedentata ( Crosnier 1991, fig. 63a). It is noteworthy that the above species groupings are relevant only with respect to female genital morphology ( Crosnier 1991).

Figures

Figure 2. Metapenaeopsis difficilis Crosnier, 1991: (a) female, lateral view; (b) pleon, dorsal view; (c) thelycum, ventral view. Scale bars: a = 10 mm; b, c = 500 μm.

Figure 3. Map indicating the geographical distribution of Metapenaeopsis difficilis Crosnier, 1991 in the Indo-Pacific oceans.