Wolfenden, 1905
Short Description:
Geatanus antarcticus is an aetideid calanoid copepod known after both sexes (female 7.60-9.08 mm in length) from the Atlantic, Pacific and Indian Ocean, mainly meso-bathypelagic.
Taxonomic Description:
Female. Total length 7.60-9.08 mm. Cephalothorax about 5 times longer than abdomen. Frontal spine not large, directed forward and slightly curved to rostrum. Spines on Th5 posterior corners curved and removed to ventral part of posterior Th5 border (lateral view). They exceed the midlength of genital segment and nearly reaching the posterior border of segment. A1 nearly as long as the body. Re1 A2 with 1, Re2 A2 with 3 setae. Md palp base with 2, Ri1 Md with 2, Ri2 Md with 9 terminal and 2 very small posterior setae. Second internal Mx1 lobe with 5, third with 4 setae and small teat, Ri with 15 setae. Mxp protopodite with lateral plate. P1 with 3-segmented Re, supplied with external spine on each segment. Ri P2 2-segmented. P4 coxopodite with 38 spines.
Male. (Description after Grice and Hulsemann (1967) with modifications). Under the name G. robustus Grice and Hulsemann (1967) figured a male that I consider to be G. antarcticus. Frontal spine present. It is curved to rostrum (lateral view). Th5 posterior corners with small spine each. P5 very close to that of G. robustus. Re3 P5 left bilobated with clear subdivision into 2 lobes, not stylet-like, it is shorter than Re2 P5 of its leg.
Remarks. Gaetanus brevicaudatus Wolfenden, 1911 also known under the new name Gaetanus wolfendeni Park, 1975 should be synonymized with Gaetanus antarcticus Wolfenden, 1905. The only distinction the species described by Wolfenden (1911) is the lesser size (5.9 mm) than in G. antarcticus. In other features (frontal spine shape, shape of spines on Th5 corners, P1 setation and presence of lateral plate on Mxp protopodite) they are identical.
Vertical distribution:
Th species was found from mesopelagic and bathypelagic (Hardy and Gunther, 1935; Vervoort, 1957), in total hauls from 500-600 m (Grice and Hulsemann, 1967; Wilson, 1950), however more often in hauls from depths more then 1000 m.
Geographical distribution:
In the Atlantic Ocean the northernmost locality: near the north-western coast of Africa (Vives, 1982) in the region of 30°N, the southernmost (after copepodite stages) from the region of South Georgia (Hardy and Gunther, 1935); in the Indian Ocean the northernmost are findings in the Gulf of Oman and the Arabian Sea (Sewell, 1947); also found in the south-eastern part of the Indian Ocean (Grice and Hulsemann, 1967) and its antarctic sector to the south off 60°S (Wolfenden, 1905; Vervoort, 1957; Markhaseva, 1996); in the Pacific Ocean recorded in the north-western part in the Izu region (Tanaka and Omori, 1970a) and the Marquesas Islands (Wilson, 1950), in the south-eastern part of the Pacific Ocean (Grice and Hulsemann, 1968; Bjornberg, 1973; Park, 1978; Markhaseva, 1996), in the antarctic part of the Pacific Ocean (Markhaseva, 1996), to the South till 71°S (Farran, 1929).
Type locality: 64°18'S 90°27'E (Wolfenden, 1905).
Material examined:
7 females from samples 379, 382, 383, 443. See examined samples module.