Sars, 1900
Short Description:
Gaetanus tenuispinus is an aetideid calanoid copepod known after both sexes (female 3.00-3.80 mm and male 2.00-3.43 mm in length). Cosmopolitan species, mostly meso-bathypelagic, but also found in epi- and abyssopelagic.
Taxonomic Description:
Female. Total length 3.00-3.80 mm. Cephalothorax about 3.6-3.8 times longer than abdomen. Frontal spine absent. Posterior Th5 corners with spines always exceeding the midlength of genital segment, usually they cover three-four fifths (3-4/5) of genital segment length, sometimes reaching its posterior border. A1 reaching the midlength of abdomen, or the end of caudal rami. Re1 A2 lacking setae, Re2 A2 with 2 setae. Md palp base with 2 setae, Ri1 Md with 2 (1 of them very small and hardly visible) setae, Ri2 Md with 9 terminal setae. Mx1 with 4 setae on the second internal Mx1 lobe, Ri with 15 setae. Lateral plate on Mxp protopodite absent. P1 with indistinct subdivision between Re1 and Re2 (some authors noted the complete division (Park, 1975b)). External spines on Re2 P1 covering about one third of the next segment length, external spine on Re3 P1 of about the same length as its segment. Ri P2 2-segmented. P4 coxopodite with group of thin spines, there are about 20.
Male. Total length 2.00-3.43 mm. Cephalothorax about 3 times longer than abdomen. Th5 posterior corners with spines, strongly varying in length, usually they are longer than Abd1, but sometimes equal in length, or even shorter. A1 reaching about the midlength of abdomen. A2 setation as in females, reduced on Ri2 A2, Ri1 A2 much thicker than in females. Md palp base with 1 seta, Ri2 Md with 9 terminal setae. First-third internal Mx1 lobes reduced, protopodite base and Ri together with about 7-8 setae (12 after Tanaka and Omori (1970a)), Re with 11, external lobe with 7 setae. Mxp protopodite with 2 (3 setae after Park (1975b)) setae in distal group. Re P1 incompletely 3-segmented, Re2 P1 often with rudimentary external spine (after Park (1975b) - 3-segmented). Ri P2 2-segmented. P4 coxopodite without spines and hairs. Re3 P5 left stylet like, not bilobated of about the same length as Re3 of its leg. Ri P5 left covering about four fifth of Re1 P5 left length.
Vertical distribution:
Mostly meso-bathypelagic species, rare in abyssal (Wheeler, 1970), in Arctic Basin recorded in hauls from epipelagic (Johnson, 1963; Markhaseva, 1996), in Antarctic sometimes between 100 and 250 m.
Geographical distribution:
Cosmopolitan species; widespread in the northern part of the Atlantic Ocean (however between 19°N and equator only single findings are known (Wheeler, 1970)), in the southern part between 30°S (Wolfenden, 1911) and the region of South Georgia (Hardy and Gunther, 1935). Widespread in the Norwegian and Greenland seas, found in the central part of Arctic Basin to 86°N (Johnson, 1963, Markhaseva, 1996). In the Indian Ocean rare, found once to the north from equator (Grice and Hulsemann, 1967), more often occurs in subantarctic antarctic part of Ocean, goes to the South to 65°S (Vervoort, 1957; Markhaseva, 1996). In the Pacific Ocean: the Bering Sea, along north-western coast of the Pacific Ocean, in the region of Aleutian Slope (Markhaseva, 1996), off California (Wilson, 1950), in the south-eastern and south-western parts of Ocean (New Zealand region) (Bjornberg, 1973; Bradford and Jillett, 1980; Markhaseva, 1996), widespread in the antarctic part of the Pacific Ocean, to the South to 68°S (Markhaseva, 1996).
Material examined:
About 200 females and 7 males from samples 62, 64, 80, 90, 92, 119, 134-137, 145, 158, 171-173, 188, 194, 201, 202, 380, 404, 405, 430, 432-436, 445-449, 451, 457, 464, 469, 470, 474, 479, 482, 522, 524, 529, 534, 535, 538, 542, 545, 546, 549, 551, 555. See examined samples module.