Bioacoustics of Metopa gigas

Note . Specimens in the ZMUC collections here marked * were reported as Metopa clypeata (Kr) by Stephensen (1931, 1944). Description . (Based on holotype ). Head length (tip of rostrum to pereonite 1) as pereonite 1 and half of 2 combined; interantennal lobe strongly projecting, broadly rounded; eyes small, round, occupying approximately 1/ 3 of head length level with eye; frons projection below the rostrum in a right angled blunt triangle between eye lobes, widely separated from irregularly rounded epistome projecting well beyond upper lip. Pereonites dorsally with low, broad ‘saddle’ in posterior half, weak in 1 and 2, increasingly more pronounced in more posterior pereonites; pleonites with similar ‘saddle’. Pereonites 1–4 increasing in length, 5–7 of equal length, all slightly shorter than 4. Pleonites 1–3 of subequal length, all about as long as pereonite 7; pleonal side plate 1 ventrally rounded, 2 and 3 rectangularly pointed. Coxal plate 2 roundedly pointed apex, with weak concavity posterodistally; plate 3 evenly convex distally; plate 4 as long as pereonites 2–5 combined along their ventral margins, 1.8 longer than mid depth; plates 5 and 6 with posterior lobe. Antenna 1 as long as head, pereonites and pleonites 1 and 2 combined along dorsal curvature; peduncle articles 1 and 2 of equal length; flagellum of 36 articles, each with 2 short aesthetascs. Antenna 2 as long as head, pereonites 1–5 and half of 6 combined, peduncle articles 4 and 5 of equal length, flagellum 4/5 length of peduncle article 5, with about 11 article. Left mandible lacinia mobilis serrate, nearly as broad as equally serrate incisor; body medially with ridge and low hump; palp of 1 article (probably damaged; see Remarks below). Right mandible incisor as in left; lacinia composed of 2 separate flattened setae; body medially with low hump carrying 5 short, stiff setae; palp of 2 articles, article 1 elongate with lateral row of simple setae; article 2 about 1/5 length of 1, with a few terminal setae. Maxilla 1 palp with row of 11 robust setae in distal half of medial margin and apically, distal surface with cover of small setae and setules; outer lobe with 7 smooth spine-setae. Maxilliped outer plate vestigial; inner plates fused with apical notch and small marginal setae. Gnathopod 1 slender, merus projecting under carpus; carpus elongate, about twice as long as propodus, densely setose along posterior margin; propodus simple; dactylus short, with row of setae on posterior margin. Gnathopod 2 merus in lateral view with acutely pointed projection covering entire carpus and about 1/5 of propodus, with transverse rows of small robust setae along posterior margin, in medial view with rounded dorsal lobe with a few small robust setae; carpus dorsal margin with row of stridulating knobs, in medial view with anterodorsal acute projection, posterior lobe with fringe of simple setae; propodus as long as basis, slightly widening distally, palm convexly transverse, crenulated, posteriorly defined by deep notch and strong tooth. Pereopod 3 thin, slightly longer than 4, with short simple setae only. Pereopod 4 robust, posterior margins of merus, carpus and propodus with a few transverse rows of small robust setae. Pereopod 5 basis rectilinear with row of long simple setae in proximal half of anterior margin; merus, carpus and propodus anterior margin with several transverse rows of small robust setae. Pereopods 6–7 basis posteriorly broadly expanded, basis of 6 anterior margin with row of small robust setae, of 7 with a few simple setae; merus, carpus and propodus of both armed as in pereopod 5. Uropod 1 peduncle slightly longer than urosomite 1, dorsolateral margin with about 21 robust setae, dorsomedial margin with 7 robust setae; outer ramus 0.8 length of peduncle, with 4 dorsal robust setae, inner ramus as long as outer, smooth, both up-curved distally. Uropod 2 peduncle 0.8 length of uropod 1 peduncle, dorsolateral margin with 10 robust setae, dorsomedial margin with a few scattered robust setae; outer ramus 0.75 length of peduncle, slightly up-curved, dorsolaterally with 3 robust setae; inner ramus as long as peduncle, smooth, slightly up-curved distally. Uropod 3 peduncle 2.8 times longer than greatest lateral width, dorsolaterally with 4 robust setae, subequal in length to uropod 2 peduncle, with dorsoapical projection; article 1 of ramus about 2/3 length of peduncle, with dorsoapical group of small robust setae; article 2 of ramus about 4/5 length of article 1, tapering, smooth. Telson oval, slightly broader in distal half, with 2 blunt robust setae each side in proximal half, single simple seta each side in distal half. Size . Largest male, 19.2 mm; largest female, 19.1 mm.