Hyperoche macrocephalus, Zeidler, Wolfgang, 2015

Zeidler, Wolfgang, 2015, A review of the hyperiidean amphipod genus Hyperoche Bovallius, 1887 (Crustacea: Amphipoda: Hyperiidea: Hyperiidae), with the description of a new genus to accommodate H. shihi Gasca, 2005, Zootaxa 3905 (2), pp. 151-192 : 180-182

Hyperoche macrocephalus sp. nov.

( Fig. 15 )

Material examined. Holotype: Female (3.8 mm), mid-eastern Indian Ocean, off Sumatra [00°51.5’S 99°24.5’E], Dana stn. 3821 II, 600 mw, 14 September 1929; ZMUC CRU- 20292.

Paratypes: Three females (all about 3 mm), collected with holotype; ZMUC CRU- 20293. One female (4.1 mm), Mediterranean Sea, east of Tunis [36°39’S 08°06’W], Dana stn. 4147 VIII, 600 mw, 10 June 1930; ZMUC CRU- 20294.

Diagnosis. Females: Sexually mature at about 4 mm. Antennae 1 relatively short, about half as long as head, marginally longer than A2. Head relatively large, length equal to first four pereonites combined. Pereon globular, length about 1.4 x pleon. Gnathopod 1; basis sub-equal in length to carpus and propodus combined; merus produced into sharp process, barely spoon-shaped, projecting under carpus, just beyond mid-point of anterior margin of propodus; carpus relatively narrow with sharp, dactyl-like tip, extending slightly past distal margin of propodus, anterior margin denticulate except for dactyl-like tip; propodus also relatively narrow, with denticulate posterior margin; dactylus slightly curved, length about one-third propodus. Gnathopod 2 slightly longer than G1 but similar in structure except that the merus is not produced as far under the carpus. Pereopod 3 slightly longer than P4–7; basis length about 2.6 x merus; carpus with postero-distal corner slightly produced, with denticulate posterior margin, slightly longer than merus and about 0.7 x propodus; postero-distal corner of propodus slightly excavate with slightly longer setae/denticles proximally, remainder of posterior margin finely denticulate; dactylus length almost 0.4 x propodus. Pereopod 4 marginally shorter than P5–7; similar in structure to P3 except the basis and propodus are relatively shorter. Pereopods 5–7 are similar in size and structure. Pereopod 5; basis length slightly more than twice merus; carpus length about 1.3 x merus, equal to propodus; dactylus length about half propodus. Pereopods 6 & 7; like P5 but basis marginally longer, especially P7, and P7 with coxa fused with pereonite. Epimeral plates with postero-distal corner rounded. Uropod 1; peduncle reaching just beyond limit of peduncle of U2 and middle of peduncle of U3; inner ramus slightly longer than outer, slightly shorter than peduncle. Uropod 2; inner ramus marginally longer than peduncle, about 1.3 x outer ramus. Uropod 3; inner ramus slightly shorter and marginally wider than outer, length about 0.7 x peduncle. Telson triangular, as long as wide, length half of peduncle of U3.

Males: Unknown.

Remarks. This species is most similar to H. mediterranea but is readily distinguished from it and all other congeners by the relatively large head and the structure of the gnathopoda and pereopods 3 & 4. The gnathopoda are relatively more slender than for any other species with the carpus and propodus more slender and elongate; together as long, or marginally longer, than the basis. Also, the postero-distal process of the merus is more pointed and less cup-shaped than for any other species. A unique character of pereopods 3 & 4 is that the postero-distal corner of the propodus is slightly excavate and devoid of setae, but the posterior margin is armed with several long, fine setae/denticles, proximally to the excavation, and with slightly shorter ones along the posterior margin. In all other species the setae/denticles on pereopods 3 & 4 are more or less evenly spread and of similar length, although females of H. mediterranea sometimes have a few longer setae near the postero-distal corner.

The paratype female from the Mediterranean Sea is like the holotype and the paratypes in all respects, indicating that this species has a wide distribution and most likely has not been recorded until now having been mistaken for H. mediterranea .

Distribution. Known only from the type locality, off Sumatra, and the Mediterranean Sea, near Tunis, as detailed above.

Figures

FIGURE 15. Hyperoche macrocephalus sp. nov. Holotype female (3.8 mm), ZMUC CRU- 20292; S. E. Indian Ocean, off Sumatra [00 ° 51.5 ’ S 99 ° 24.5 ’ E], Dana stn. 3821 II, 600 mw, 14 Sept. 1929. Scale bars = 0.2 mm (Us), 0.5 mm (remainder).