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Giesbrecht, 1888

Short Description:

Gaetanus armiger is an aetideid calanoid copepod known after both sexes (female 2.70-4.70 and male 2.60-3.16 mm in length) from the Atlantic, Indian and Pacific oceans, mainly meso-bathypelagic and sometimes epipelagic.

Taxonomic Description:

Female. (Description after Giesbrecht (1892) and Park (1975b) with modifications). Total length 2.70-4.70 mm. Cephalothorax about 3.5 times longer than abdomen. Frontal spine present, not large, curved to rostrum. Spines on Th5 situated in the middle of posterior Th5 border (lateral view), reaching the last fourth of genital segment. A1 by 2-3 last segments longer than body. Re1 A2 lacking setae, Re2 A2 with 2 (1 medial situated on conic protrusion and 1 distal) setae. Md palp base with 2 setae, Ri1 Md with 2, Ri2 Md with 9 setae; second internal Mx1 lobe with 4 setae, Ri with 14 setae. Mxp protopodite lacking lateral plate. P1 with 3-segmented Re. Re P1 without spine, Re2 and Re3 P1 supplied with external spines. Ri P2 2-segmented. P4 coxopodite with about 14-17 setae.

Male. Total length 2.60-3.16 mm. Frontal spine very small and situated close to cephalon (lateral view) it is also removed posteriorly. Spines on Th5 posterior corners not reaching the posterior border of genital segment. A1 reaching posterior border of genital segment. Re2 A2 with 2 setae. Md palp base with 2 small setae. Ri Mx1 with 9 long setae and few very small rudimentary setae; Re with 11 and external lobe with 9 setae. Mxp protopodite with 1 medial and 3 distal setae. Re P1 3-segmented, only Re3 with normally developed external spine. P4 coxopodite lacking spines, all other features of structure of P2-P4 as in female. Both Re segments of right P5 of about equal length. Left Ri P5 nearly reaching the distal part of Re1, Re3 P5 left is stylet-like, slightly longer than Re2 of its leg.

Remarks. Park considered, that male described by Tanaka (1969) supposedly attributed to G. armiger really belongs to some other species (Park, 1975b).

Vertical distribution:

The species was found in hauls from meso-, bathypelagic (Park, 1975b) and epipelagic (Mori, 1937) and in total hauls from depths from 500 to 5000 m.

Geographical distribution:

In the Atlantic Ocean species found to the North to 61°N (Jespersen, 1934), to the South to the Gulf of Guinea, widespread to the North from equator; in the Indian Ocean in the Bay of Bengal (Sewell, 1929), in the region of the Malay Archipelago (A. Scott, 1909). In the Pacific Ocean found in the north-western (Tanaka and Omori, 1970a), northern (Wilson, 1950) and equatorial parts (Giesbrecht, 1888), the southernmost finding in the south-eastern part of the Pacific Ocean in the region of 11°S (Wilson, 1950).

Type locality: Equatorial part of the Pacific Ocean (Giesbrecht, 1888).

Material examined:

The species absent in the collections of the Zoological Institute, Russian Academy of Sciences St. Petersburg.

Gaetanus armiger