Bioacoustics of Metapenaeopsis difficilis

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)).