Gennadas gilchristi Calman 1925

Gennadas gilchristi Calman, 1925

(Figure 3 A‒C)

Amalopenaeus elegans (non Smith, 1882). — Sttebing 1917: 31.

Gennadas gilchristi Calman, 1925: 6, plate I, figs. 3, 4.— Burkenroad 1936: 79, fig. 58.— Kensley 1971: 280, fig. 6; 1972, figs. 4 f, e, 6c.—Iwasaki & Nemoto 1987: 5.— Kensley et al. 1987: 277 –278.— Dall 2001: 431, fig. 16.— Dall 2005: 413.

Material examined. Superstation 9, serial 1040, 2 Males (CL, 5.50 mm, 7.40 mm) and 1 Female (CL, 5.30 mm), Mid-Atlantic Ridge, 32°50’55.8’’S, 01°49’42’’E, 1401 m, MNRJ 22570. Superstation 8, serial 1034, 1 Female (8.43 mm), Mid-Atlantic Ridge, 30°04’10.8’’S, 02°49’58.8’’E, 1175 m, MNRJ 22569. Superstation 0, serial 1037, 2 Males (CL, 6.65 mm, 8.42 mm), Mid-Atlantic Ridge, 30°19’10.8’’S, 03°08’16.8’’E, 997 m, MNRJ 23380. Superstation 2, serial 1006, 1 Female (CL, 6.20 mm), Mid-Atlantic Ridge, 00°25’57.6’’N, 17°15’28.2’’W, 1381 m, MNRJ 22571. Superstation 7, serial 1030, 1 Female (CL, 10.36 mm), Mid-Atlantic Ridge, 29°27’39’’S, 01°08’25.8’’E, 4120 m, MNRJ 22568.

Diagnosis. Carapace thin. Antennal and infra-antennal angles apically truncated. Spine on outer margin of scaphocerite almost reaching the apex. Thelycum with 7th sternite with bilobed external process; plate of 8th sternite entire. Petasma inner lobe acute, with hooked setae in anterior and posterior margin. Median lobe with 2 slender lobules. External lobe with smaller lobe at its base. Accessory lobe broadly rounded, not extending beyond the internal lobe.

Distribution. Western Atlantic: Bahamas, Gulf of Mexico, Antilles. Eastern Atlantic: Portugal (Azores Islands), Cape Verde, Gabon, Congo, Angola, Mid-Atlantic Ridge (Walvis Ridge) (Figure 2), South Africa (Cabo da Boa Esperança). Indo-Pacific Oceans: New Zealand, New Caledonia, Australia (Crosnier & Forest 1971; Kensley 1971; Kensley et al. 1987; Dall 2001).

Bathymetric Distribution. Maximum of 3400 m depth (Kensley 1971; Kensley et al. 1987; Dall 2001). Herein this species was found in the Mid-Atlantic Ridge at total depth reaching between 997‒ 4120 m, thus extending the distribution of this species into deeper waters.

Remarks. The specimens analyzed herein fit well with the descriptions provided by Calman (1925) and Kensley (1971), but they showed some morphological variations: endopod and exopod of the first maxilliped are of the same size, while according to Calman (1925) the endopod is longer than the exopod; the antenal and infraantenal angles are truncated, the coxa is not bilobed, while Kensley (1971) observed that the antenal and infraantenal angles are rounded and the coxa is bilobed.

The closest species of G. gilchristi is G. valens (Smith, 1884), but these two species can be distinguished from each other as follow: thelycum with 7th sternite showing 2 anteriorly-directed projections apically notched in G. gilchristi vs. apically simple in G. valens; petasma of G. gilchristi with the external lobule of median lobe slender, with apex of internal lobe acute vs. external lobule of median lobe not slender and the inner lobule of median lobe blunt in G. valens. Gennadas gilchristi present a cosmopolitan distribution, being recorded more frequently in the Eastern Atlantic. Present records increase its distribution from the Mid-Atlantic Ridge (Walvis Ridge) in South Atlantic.