Esterly, 1911
Short Description:
Gaetanus secundus is an aetideid calanoid copepod known after both sexes (female 3.80-5.20 mm and male 3.00-3.55 mm in length) from the Gulf of Mexico, the Indian Ocean and the Pacific Ocean.
Taxonomic description:
Female. Total length 3.80-5.20 mm. Cephalothorax about 5 times longer than abdomen. Frontal spine present, long and robust, directed forward, its top is not curved or weakly curved to rostrum. Spines on Th5 posterior corners situated in the middle of posterior Th5 border (lateral view), straight, exceeding the middle of genital segment. A1 twice as long as body (nearly of the same length as in G. miles ). Re1 A2 without setae, Re2 A2 with 1 seta. Md palp base with 1 seta, Ri1 Md with 1, Ri2 Md with 9 terminal setae. Second Mx1 internal lobe with 3 (?) setae, Ri with 14-15 setae. Lateral plate on Mxp protopodite present. P1 with 2-segmented Re, with 2 external spines: first exceeding the midlength of last Re P1 segment. Ri P2 one-segmented, with traces of subdivision between segments. P4 coxopodite with about 13 spines.
Male. (Description after Park (1975b) with modifications). Total length 3.00-3.55 mm. Frontal spine absent. Medial crest present. Spines of Th5 posterior corners small, hardly visible, often asymmetrical. Rostrum well developed. A1 reaching the end of caudal rami. Re1 and Re2 A2 without setae. Md palp base with small setae. Mx1 with 9 setae on Ri and 11 on Re, external lobe with 7 setae. Mxp protopodite with 3 setae distally. P1 distinctly 3-segmented. External spine present only on Re3 P1. Re P5 right of 2 segments of about same length, Ri P5 left nearly reaching the midlength of Re1.
Remarks. G. secundus was united with G. miles (Vervoort, 1963: 131). I consider it wise to re-established the species status for G. secundus . Good detailed description of G. miles , supplied with good figures (Giesbrecht, 1892) and brief, but comprehensive description of G. secundus (Esterly, 1911) give a relevant base to distinguish between these two species.
Vertical distribution:
The species was found between 500 and 2000 m (Park, 1975b), also in total hauls from depths of 8000 m.
Geographical distribution:
Due to mixing of this species with G. miles it is difficult to describe its distribution: there may be mentioned the Gulf of Mexico (Park, 1975b), the Indian Ocean in the region of 28°S (Markhaseva, 1996); in the Pacific Ocean from the regions of Izu Bonin and Marianas trenches (Markhaseva, 1996) and off San Diego, California region (Esterly, 1911).
Type locality: the north-eastern part of the Pacific Ocean, San Diego region (Esterly, 1911).
Material examined :
11 females from samples 201, 202, 403, 410, 413, 416. See examined samples module.