Body clear with a whitish tint
The greatest height of the head (from side view) is almost the same as the tip of the head, so that it forms practically a straight angle. P5 three-segmented, the chaetae of the distal segment of P5 of the same length.
The caudal rami in males are longer than the anal segment; the left P5 contains 2 inner spines.
According to Mazzocchi & al. (1995) the systematic literature is contradictory and insufficient to clearly distinguish between M. pacifica and M. lucens.
North Pacific and sub-Arctic Seas. In the north goes as far as the southern Chukchi. For Kosobokova & Hopcroft (2010) this species is an Pacific expatriate in Arctic waters.
Oceanic, epi- to bathypelagic species.
Female:
The back is strongly arched from side view, the greatest height of the head (from side view) is almost the same as the tip of the head, so that it forms practically a straight angle. The posterior corners of the last thoracic segment with small sharp points, which are visible both from dorsal and side view. Abdomen almost 2 times shorter than the cephalothorax. The genital segment is approximately the same length as the next 2 segments combined. The anal segment is somewhat shorter than the caudal rami. P5 three-segmented, the distal segment carries 3 cheatae of practically equal length. This segment and also the 2nd segment each carries a long spine on its outer edge.
Male:
The distal segment of the right P5 is larger than the left and does not narrow distally. The left P5 with 2 large spines on the inner edge. The right leg is 4-segmented.
Female: 2,40-3,45 mm
Male: 1,65-2,60 mm
Metridia pacifica is a copepod found in the north Pacific and surrounding waters.
M. pacifica is most closely related to M. lucens; before being split by Brodsky based on morphological differences, these were considered to be the same species.[1]
M. pacifica has a clear body with a whitish tint.[2] In terms of length, females are range from about 2.4 to 3.5 millimetres (0.094 to 0.138 in), and males are usually between about 1.7 and 2.6 millimetres (0.067 and 0.102 in).[3]
M. pacifica is found in the north Pacific and sub-Arctic waters. It can be found north as far as the southern Chukchi Sea. It is reported to be an expatriate in the Arctic Ocean.[2]
M. pacifica has multiple broods. At Station P, for example, there are three cohorts: one in March, one in late June and July, and one in September to early October. The nauplii are generally found above depths of 500 metres (1,600 ft) (and mostly above 100 metres (330 ft), and their distribution in these surface waters varies seasonally. It is likely that this is influenced by temperature; in one study, over 85% of nauplii were found below the thermocline from 14 June until 22 September, when it is warmer at the surface.[4]
M. pacifica has an average generation time of three to four months at Station P.[4]
Metridia pacifica is a copepod found in the north Pacific and surrounding waters.
