Sars, 1907
Short Description:
Gaetanus brachyurus is an aetideid calanoid copepod known after both sexes ( female 5.00-7.15 mm and male 5.16 mm in length) from the Atlantic, Pacific and Indian oceans, mainly bathypelagic.
Taxonomic Description:
Female. Total length 5.00-7.15 mm. Cephalothorax about 5 times longer than abdomen. Frontal spine present, not large. It is curved and directed to rostrum. Spines on posterior Th5 corners straight, reaching nearly the midlength of genital segment (dorsal view), situated in the middle of posterior Th5 border (lateral view). A1 slightly shorter than body, or exceeding by 2-3 last segments. Re1 A2 with 2, Re2 A2 with 2 setae. Md palp base with 2, Ri1 Md with 2, Ri2 Md with 9 terminal setae, arranged in row and 1 posterior seta. Second Mx1 internal lobe with 5, Ri with 15 setae. Mxp protopodite with lateral plate. P1 with 3-segmented Re (in one case it is 2-segmented (Grice and Hulsemann, 1967)) supplied with external spines on each segment. Ri P2 2-segmented. P4 coxopodite with 26-30 spines.
Male. (Description after Park (1975b) with modifications). Total length 5.16 mm. Frontal spine larger than in female. Spines on posterior Th5 corners exceeding the posterior border of genital segment. A1 slightly longer than body. First 2 Re A2 segments lacking setae. Md palp base with small seta. Ri Mx1 with 9 setae, Re Mx1 with 11, external lobe with 9. Mxp protopodite with 3 setae distally. P1 with 3-segmented Re, each segment bearing external spine. P2-P4 as in female, but P4 coxopodite lacking spines. Both Re segments of right P5 of about equal length. Left Ri P5 is about one third of Re1 length, left Re3 P5 not stylet-like form, bilobated. It is less than half the length of left Re2 P5.
Vertical distribution:
The species was once found near surface (Sars, 1925), recorded in hauls from bathypelagic (Grice and Hulsemann, 1967) and in total hauls from 1500-5000 m.
Geographical distribution:
In the Atlantic Ocean found to the North to the Strait of Davis (Jespersen, 1934), known from the Gulf of Mexico (Park, 1975b), the southernmost finding in the region of 26°N (Sars, 1925). Recorded from the western part of the Indian Ocean (Grice and Hulsemann, 1967); the south-eastern part of the Pacific Ocean (Grice and Hulsemann, 1968); the north-western part of the Pacific Ocean: off the Kurile-Kamchatka Trench region (Markhaseva, 1996).
Type locality: North Atlantic, to the North of the Canary Islands (Sars, 1907).
Material examined:
1 female from sample 103. See examined samples module.