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Farran, 1903

Short Description:

Gaetanus pileatus is an aetideid calanoid copepod known after both sexes (female 4.90-6.70 mm and male 4.44-5.08 in length) from the Atlantic, Indian and Pacific oceans, mainly mesopelagic.

Taxonomic Description:

Female. Total length 4.90-6.70 mm. Cephalothorax about 5 times longer than abdomen. Frontal spine present, in anterior-dorsal part of cephalon (lateral view), directed forward, long, its top not curved to rostrum. Spines on Th5 posterior corners straight, arranged in the middle of posterior Th5 border (lateral view), exceeding the middle of genital segment, covering nearly two third of its length, slightly divergent (dorsal view). A1 by 5-7 last segments longer than body. Re1 A2 without setae, Re2 A2 with 1 seta. Second Mx1 internal lobe with 4 setae, third additionally to setae bears small sensitive teat; Ri with 14-15 setae. Md palp base with 2, Ri1 Md with 1, Ri2 Md with 9 terminal setae. Lateral plate on Mxp protopodite present, P1 with 2-segmented Re, supplied with external spines on each segment. First external spine not reaching the middle of the next segment. P4 coxopodite with 17-20 spines.

Male. Total length 4.44-5.08 mm. Frontal spine large, strongly curved to rostrum. Spines on Th5 posterior corners small. A1 reaching Abd3-4. Both Re segments of right P5 of about equal length. Ri P5 left is about half, or one third of Re1 P5 length, Re3 P5 nearly two third of Re2 P5 length, stylet-like, not bilobated.

Remarks. As noted earlier (Park, 1975b) shape and length of frontal spine is highly varying. There is an opinion that this variability is connected with the size of specimens: larger specimens usually with larger and directed more backwards frontal spine. Shape of lateral plate on Mxp protopodite is also variable (Park, 1975b).

Vertical distribution:

The species is found in hauls from mesopelagic (Farran, 1926; Sewell, 1947; Park, 1975b; Bradford and Jillett, 1980; Vives, 1982) and total hauls from depths from 600 to 5000 m.

Geographical distribution:

In the Atlantic Ocean the northernmost locality: in the region of 65°N (With, 1915), the southernmost: the Gulf of Guinea (Vervoort, 1963), in the Arabian Sea and the Bay of Bengal, and the southernmost in the Indian Ocean in the region of 45°S 125°E (Markhaseva, 1996); in the Pacific Ocean the northernmost findings: Izu region (Tanaka and Omori, 1970a) and San Diego region (Esterly, 1911), the southernmost: in the region of 56°S (Park, 1978). The species occurs in tropical and subtropical zones of all oceans.

Type locality: south and south-western coasts of Ireland, Atlantic Ireland slope (Farran, 1903).

Material examined:

8 females from samples: 392, 400, 403, 419?, 443, 444, 447, 449. See examined samples module.

Gaetanus pileatus