Farran, 1908
Short Description:
Chiridius gracilis is an aetideid calanoid copepod known after both sexes (female 2.45-2.80 mm and male 1.96-2-32 mm) from World Ocean, mainly mesopelagic.
Taxonomic Description:
Female. Total length 2.45-2.80 mm. Cephalothorax 3.21-4.20 times longer than abdomen ( in the first description (Farran, 1908) abdomen recorded as 2.5 times shorter than cephalothorax). Posterior points of Th5 corners exceeding the midlength of genital segment (usually they reach the end of second third of segment length). Genital segment is the widest in its middle length. A1 as long as cephalothorax, or reaches the end of genital segment (or to the middle of Abd2 (Park, 1975)). Ri2 Md with 9 setae (sometimes there are 8). Re Mx1 with 8 setae. External spine of Re P1 not reaching (rarely exceeding) the base of following spine. Re P2 - 3-segmented (sometimes subdivision between Re1 and Re2 is incomplete); Ri P2 indistinctly 2-segmented, usually not reaching (rarely reaching) border between Re2-Re3 P2. Re3 P2 without excavation between second and third external spines; first and second external spines long, reaching the base of the next spine.
Male. Total length 1.96-2.32 mm. Cephalothorax 3.1 times longer than abdomen (2.6 times after Tanaka (1957)). Posterior points of Th5 corners are not longer than Abd1. A1 23-segmented, shorter than cephalothorax. Ri2 Md with 8 long setae and 1 short seta. Mx1 with 2 setae on second (?) internal lobe, Re with 9 setae, Ri also with 9 setae. Ri1 Mxp with 3 medial setae. External spines of Re1 and Re2 P1 not reaching the bases of next spines. P2 with incompletely 2-segmented Ri. First and second external spines on Re3 P2 reaching the base of following spine, Ri reaching the border between Re2-Re3 P2.
Vertical distribution:
The species recorded in the majority of total hauls from depths 300-8300 m, and in hauls from 500-1000 m (Park, 1975a). Most possibly mesopelagic species, most common in total hauls from 500 to 1000 m.
Geographical distribution:
Atlantic Ocean: the northernmost finding in the Norwegian Sea (71°N), the southernmost in the region of the South Sandwich Islands. Pacific Ocean: the northernmost finding from the Izu region (Tanaka and Omori, 1970a), the southernmost from the antarctic sector of the Pacific Ocean (region of 62°33'S 127°37'W, Markhaseva, 1996). Indian Ocean: the species was found in the north-eastern part (Markhaseva, 1996).
Type locality: the North Atlantic to the west of Ireland (Farran, 1908).
Material examined:
34 females and 3 males from samples: 2, 201, 215, 274, 280, 346, 347, 350-352, 354, 355, 358, 359, 361, 364, 373, 375, 419, 426, 432, 438, 451, 465. See examined samples module.