Sars, 1907
Short Description:
Gaetanus minutus is an aetideid calanoid copepod known after both sexes (female 2.30-3.70 mm and male 1.70-3.40 mm in length) from the Atlantic, Pacific and Indian oceans, epi- and meso-bathypelagic.
Taxonomic Description:
Female. Total length 2.30-3.70 mm. Cephalothorax 3-4 times longer than abdomen. Posterior Th5 corners with spines of variable size, often asymmetrical, of different shape, sometimes covering first third of genital segment length, sometimes reduced to small knobs. A1 longer than cephalothorax, reaching the end of genital segment, or the end of caudal rami. Re1 A2 without setae, Re2 A2 with 2 setae. Md palp base with 2 (Tanaka and Omori (1970a) recorded 3 setae), Ri1 Md with 2 setae (1 of them small, poorly visible) setae, Ri2 Md with 9 terminal setae. Second internal Mx1 lobe with 4 setae, Ri with 14 setae. Mxp protopodite without lateral plate. P1 with indistinctly 3-segmented Re, Re1 and Re2 incompletely fused, line of fusion visible, Re with 2 external spines. P2 with 2-segmented Ri and 3-segmented Re. P4 coxopodite with 17-20 spines.
Male. Total length 1,70-3.40 mm. Cephalothorax about 3.0-3.4 times longer than abdomen. Frontal spine absent. Shape and length of spines on Th5 posterior corners varies strongly like in female, but usually they do not reach posterior Abd1 border. A1 longer than cephalothorax, sometimes shorter, often reaching the end of caudal rami. Setation of oral parts reduced in comparison with that in female. Segmentation of P2-P4 as in female, first external Re spine reduced to very small. P4 coxopodite without spines. Left Re3 P5 not bilobated, stylet-like. P5 similar to that of G. tenuispinus.
Remarks. The species is characterized by high variability. The vast original material on the species was examined for this study, and resulted in a proposal to synonymize Gaidius variabilis Brodsky (=Gaetanus variabilis (Brodsky)) with G. minutus (Sars, 1907). The latter species was recently redescribed by Park (1975b) in details. This detailed redescription has permitted to clarify the status of G. variabilis.
Vertical distribution:
The species was found in hauls from epipelagic and meso-bathypelagic, also in total hauls from 500-7500 m.
Geographical distribution:
In the Atlantic Ocean species was found to the North to 48°N (Lysholm, Nordgaard and Wiborg, 1945), to the South to the Gulf of Mexico (Park, 1975b); in the south-western part of the Indian Ocean between 10°N and 6°S (Sewell, 1929; Grice and Hulsemann, 1967); in the Pacific Ocean known from the Sea of Okhotsk, the Bering Sea and the Sea of Japan, from the Izu region, regions of the Kurile-Kamchatka and Marianas Trench (Brodsky, 1950; Tanaka and Omori, 1970a, Markhaseva, 1996), recorded also in the north-eastern part: the region of British Columbia, from the Strait of Georgia (Park, 1967), from the eastern tropical Pacific (Wilson, 1950) and New Zealand region (Bradford and Jillett, 1980).
Type locality: region of 36-46°N and 7-27°W (Sars, 1925).
Material examined:
250 females and 10 males from samples: 18, 60-64, 71-73, 78-82, 89-95, 118-120, 123, 132, 134-137, 145, 146, 156-160, 169-174, 182-186, 188-191, 201, 204, 205, 216-219, 221, 222, 224, 225, 227-229, 230, 232-237, 239, 240, 242, 244, 246, 248, 250, 474. See examined samples module.