( Fig. 1)
Gnathophausia gigas Willemoes-Suhm, 1873: 400 –401.—G.O. Sars 1885: 33–35.—Ortmann 1906: 36–38. —W.M. Tattersall 1939: 225.—Fage 1941: 24–27.—Banner 1948: 357–358.—Tattersall and Tattersall 1951: 77–82.— O.S. Tattersall 1955: 36–38.—Kathman et al. 1986: 158–159.—Casanova et al. 1998: 60.
Gnathophausia drepanephora Holt and Tattersall, 1905: 113 –116.
Neognathophausia gigas— Petryashov 1992: 47–48.
Material examined. In formaldehyde (transferred to ethanol). Stn 2-326 - 1001, 9 specimens (ZMBN 81183, ZMBN 81184); Stn 2-327 - 1005, 2 specimens (ZMBN 81185); Stn 2-327 - 1006, 1 specimen (ZMBN 81186); Stn 2- 327 - 1008, 1 specimen (ZMBN 81187); Stn 4-328 - 1009, 2 specimens (ZMBN 81188); Stn 4-329 - 1014, 1 specimen (ZMBN 81189); Stn 6-331 - 1021, 2 specimens (ZMBN 81190); Stn 6-331 - 1022, 7 specimens (ZMBN 86549); Stn 6-331 - 1023, 2 specimens (ZMBN 81192); Stn 7-332 - 1025, 1 specimen (ZMBN 81193); Stn 8-333 - 1026, 4 specimens (ZMBN 81194); Stn 8-333 - 1027, 15 specimens (ZMBN 81195); Stn 8-333 - 1028, 1 specimen (ZMBN 81196); Stn 8-333 - 1029, 3 specimens (ZMBN 81197); Stn 8-333 - 1030, 1 specimen (ZMBN 81198); Stn 8-334 - 1031, 4 specimens (ZMBN 81199); Stn 11-337 - 1040, 7 specimens (ZMBN 81200, ZMBN 81201); Stn 12-338 - 1042, 2 specimens (ZMBN 81203); Stn 12-338 - 1043, 2 specimens (ZMBN 81204); Stn 12-339 - 1046, 9 specimens (ZMBN 81205); Stn 14-340 - 1049, 1 specimen (ZMBN 81206); Stn 14-340 - 1050, 3 specimens (ZMBN 81207); Stn 14-340 - 1051, 9 specimens (ZMBN 81208); Stn 14-340 - 1053, 4 specimens (ZMBN 81209); Stn 14-341 - 1054, 6 specimens (ZMBN 81210); Stn 14-341 - 1056, 1 specimen (ZMBN 81211); Stn 16-343 - 1058, 3 specimens (ZMBN 81212); Stn 16-343 - 1059, 6 specimens (ZMBN 81213); Stn 16-343 - 1060, 9 specimens (ZMBN 81214); Stn 16- 343 - 1061, 4 specimens (ZMBN 81215); Stn 18-345 - 1066, 4 specimens (ZMBN 81216); Stn 18-345 - 1067, 3 specimens (ZMBN 81217); Stn 18-345 - 1068, 13 specimens (ZMBN 81218); Stn 18-345 - 1070, 1 specimen (ZMBN 81219); Stn 18-346 - 1071, 4 specimens (ZMBN 81220); Stn 18-346 - 1072, 13 specimens (ZMBN 81221); Stn 20- 347 - 1075, 3 specimens (ZMBN 81222); Stn 20-347 - 1076, 19 specimens (ZMBN 81223); Stn 20-347 - 1077, 1 specimen (ZMBN 81224); Stn 20-348 - 1079, 3 specimens (ZMBN 81225); Stn 20-348 - 1080, 17 specimens (ZMBN 81226, ZMBN 81227); Stn 20-348 - 1081, 1 specimen (ZMBN 81228); Stn 22-349 - 1082, 9 specimens (ZMBN 81229, ZMBN 81230); Stn 22-349 - 1083, 2 specimens (ZMBN 81231); Stn 22-349 - 1084, 6 specimens (ZMBN 81232); Stn 22-350 - 1087, 6 specimens (ZMBN 81233); Stn 22-350 - 1088, 9 specimens (ZMBN 81234); Stn 22- 350 - 1089, 1 specimen (ZMBN 81235); Stn 24-351 - 1090, 2 specimens (ZMBN 81236); Stn 24-351 - 1091, 5 specimens (ZMBN 81237); Stn 24-351 - 1092, 4 specimens (ZMBN 81238); Stn 24-351 - 1093, 1 specimen (ZMBN 81239); Stn 24-351 - 1094, 1 specimen (ZMBN 81240); Stn 24-352 - 1095, 6 specimens (ZMBN 81241); Stn 24-352 - 1096, 5 specimens (ZMBN 81242); Stn 26-354 - 1103, 21 specimens (ZMBN 81243, ZMBN 81244, ZMBN 81245); Stn 28-356 - 1109, 4 specimens (ZMBN 81246); Stn 28-356 - 1110, 16 specimens (ZMBN 81247, ZMBN 81248); Stn 28-356 - 1112, 1 specimen (ZMBN 81249); Stn 28-357 - 1114, 3 specimens (ZMBN 81250); Stn 28-357 - 1115, 2 specimens (ZMBN 81251, ZMBN 81252); Stn 30-358 - 1117, 4 specimens (ZMBN 81253); Stn 30-358 - 1118, 7 specimens (ZMBN 86558); Stn 30-358 - 1119, 10 specimens (ZMBN 81254); Stn 30-358 - 1121, 1 specimen (ZMBN 81255); Stn 30-359 - 1122, 9 specimens (ZMBN 81256); Stn 30-359 - 1123, 5 specimens (ZMBN 81257); Stn 30- 359 - 1124, 1 specimen (ZMBN 81258); Stn 31-360 - 1199, 7 specimens (ZMBN 81259); Stn 32-361 - 1126, 13 specimens (ZMBN 81260), 1 specimen (ZMBN 81261), 2 specimens (ZMBN 81262); Stn 32-362 - 1128, 2 specimens (ZMBN 81263); Stn 32-362 - 1129, 2 specimens (ZMBN 81264); Stn 32-362 - 1130, 10 specimens (ZMBN 81265); Stn 34-363 1133, 3 specimens (ZMBN 81266); Stn 34-363 - 1134, 2 specimens (ZMBN 81267); Stn 34-363 1135, 12 specimens (ZMBN 81268); Stn 34-363 - 1137, 3 specimens (ZMBN 81269); Stn 34-364 - 1138, 7 specimens (ZMBN 81270), 7 specimens (ZMBN 81271); Stn 34-364 - 1139, 4 specimens (ZMBN 81272, ZMBN 81273); Stn 34-364 - 1140, 1 specimen (ZMBN 81274); Stn 36-365 - 1141, 4 specimens (ZMBN 81275); Stn 36-365 - 1142, 7 specimens (ZMBN 81276); Stn 36-365 - 1143, 9 specimens (ZMBN 81277); Stn 36-365 - 1144, 2 specimens (ZMBN 81278); Stn 36-365 - 1145, 6 specimens (ZMBN 81279); Stn 36-366 - 1146, 5 specimens (ZMBN 81280); Stn 36-366 - 1147, 3 specimens (ZMBN 81281); Stn 36-366 - 1148, 1 specimen (ZMBN 81282); Stn 40-367 - 1149, 6 specimens (ZMBN 81283, ZMBN 81284); Stn 42-368 - 1150, 2 specimens (ZMBN 81285, ZMBN 81286); Stn 44- 369 - 1151, 1 specimen (ZMBN 81287); Stn 46-372 - 1154, 1 specimen (ZMBN 81288); Stn 50-373 - 1155, 2 specimens (ZMBN 81289); Stn 52-374 - 1156, 1 specimen (ZMBN 81290); Stn 54-377 - 1159, 2 specimens (ZMBN 81291); Stn 56-378 - 1160, 4 specimens (ZMBN 81292); Stn 66-383 - 1165, 1 specimen (ZMBN 81293).
In ethanol. Stn 7-332 - 1025, 24 specimens (ZMBN 86522); Stn 8-334 - 1031, 6 specimens (ZMBN 86524); Stn 8-334 - 1033, 2 specimens (ZMBN 86527); Stn 10-335 - 1035, 7 specimens (ZMBN 86550); Stn 11-337 - 1040, 3 specimens (ZMBN 86529); Stn 12-338 - 1042, 4 specimens (ZMBN 86562, ZMBN 86563, ZMBN 86565, ZMBN 86567); Stn 12-338 - 1043, 3 specimens (ZMBN 86551, ZMBN 86561, ZMBN 86564); Stn 12-339 - 1046, 10 specimens (ZMBN 86530); Stn 14-340 - 1051, 4 specimens (ZMBN 86552, ZMBN 86560, ZMBN 86566); Stn 18- 346 - 1072, 13 specimens (ZMBN 86535); Stn 10-335 - 1087, 22 specimens (ZMBN 86627, ZMBN 86537); Stn 24- 351 - 1091, 2 specimens (ZMBN 86557); Stn 24-352 - 1096, 7 specimens (ZMBN 86538); Stn 30-359 - 1123, 3 specimens (ZMBN 86540); Stn 36-366 - 1147, 1 specimen (ZMBN 86542).
Frozen (transferred to ethanol). Stn 8-334 - 1033, 2 specimens (ZMBN 86527); Stn 14-340 - 1052, 1 specimen (ZMBN 86553); Stn 15-342 - 1057, 44 specimens (ZMBN 86554, ZMBN 86555, ZMBN 86556, ZMBN 86622, ZMBN 86623, ZMBN 86625).
Diagnosis. Body broad. Carapace thin and fragile; rostrum shorter than carapace, denticulate; posterodorsal spine barely visible in adults; median dorsal keel interrupted in region of cervical groove, forms raised keel proximal to rostrum and extends posteriorly to posterodorsal end; ventral lateral extensions of carapace produced into posterolateral spines, longest in young specimens; upper and lower lateral keels end on posterior margin; branchiostegal spines well developed; antennal and supra-orbital spines obsolete. Antennal scale without apical suture, spines on outer margin increase from two to five as growth proceeds. Ventrolateral margins of abdominal somites extending into two lobes, frontal lobe rounded, distal lobe produced into spine. Telson large, linguiform, continuing past the uropods, apex extends outwards forming lappets. Obtains lengths up to 160 mm.
Distribution. The species G. gigas was captured at all Mar-Eco stations, and was evenly distributed along the ridge. It was found from the surface down to 3000 m. G. gigas has a deeper distribution than G. z o e a, and was most abundant from 1500 m up to 600 m at most stations.
During the voyage of the “H.M.S. Challenger” one specimen of G. gigas was captured in the north Atlantic to the west of the Azores at a depth of 4024 m (G.O. Sars 1885).
With the U. S. Bureau of Fisheries steamer “Albatross” five specimens were collected at four localities (Ortmann 1906). One was captured in the north-west Atlantic between Cape Charles and Long Island at a depth of 1558 m. The other four were collected in the north Pacific around Alaska at depths of 1602 m (between Sitka and Columbia River), 730 m (Bering Sea) and 1271 m (between Unalaska and Kodiak). The Discovery expedition (O.S. Tattersall 1955) recorded G. gigas from mostly the south Atlantic, but also from the central Indian Ocean and Bellingshausen Sea. The greatest depth from where it was captured was at 2500 - 2000 m (west of Cape Town), and the shallowest at 700 to 400 m (north-west of Bouvet).
Remarks. Morphogenesis is conspicuous in G. gigas. With age the rostrum, posterodorsal and posterolateral spines of the carapace become progressively shorter and there is an increase in the number of spines on the outer margin of the antennal scale from two to four or five. In young specimens the epimera of the sixth abdominal somite are separate, during growth the epimera gradually fuse forming a heart-shaped plate with an incision at the posterior end. Morphological differences between young and old specimens led Holt and Tattersall ( 1905) to describe a young specimen of G. gigas as a new species, G. drepanephora. This specimen was later identified by Ortmann ( 1906) as a young G. gigas.
Based on shared morphological traits in the antennal scale and telson, Petryashov ( 1992) proposed that G. gigas and G. i n g e n s should be placed in a new genus, Neognathophausia. Later, Casanova et al. ( 1998) rejected Neognathophausia following an argument first proposed by O.S. Tattersall ( 1955), namely, that it would prove problematic to erect a new genus for these two species, this due to the fact that a third species, G. gracilis, has shared morphology with both Gnathophauia and Neognathophausia. Further strengthening this argument, Casanova et al. ( 1998) demonstrated through a molecular analyses with morphological support (presence of an anterodorsal tooth in the cardiac chamber), that G. gracilis would fall basal to a Neognathophausia + remaining Gnathophausia monophyly. In effect, to accept Neognathophausia one would render the Gnathophausia as polyphyletic. Consequently, we find the establishment of a non-monophyletic taxa unnecessary and dismiss the erection of Neognathophausia.