Overview

Comprehensive Description

Biology

Notes:

Remarkably close to P. japonica; most authors, commencing with Barnard, have considered P. pacifica a synonym of the former. However, Bowman studied in detail the fauna of the genus Parathemisto in the northern part of the Pacific Ocean and showed that there are constant, albeit insignificant, differences between these two species. In those few regions where the areas of description overlap, the affinity of the crustaceans to one or the other species can be adequately and definitely established. [Stebbing, 1888]
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Distribution

Sub-Arctic waters of the northern part of the Pacific Ocean and the Bering Sea. Apparently, it is absent in the Sea of Japan. It is not known whether P. pacifica penetrates into the Sea of Okhotsk and how far. [Stebbing, 1888]
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Physical Description

Size

Length of sexually mature females 4.5-8.5 mm; males somewhat smaller. [Stebbing, 1888]
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© Dunn , Adam

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Diagnostic Description

P. pacifica differs from P. japonica in much smaller size of sexually mature individuals and antennae II in females do not exceed antennae I in length as they are somewhat shorter than in the head and two subsequent somites of the pereon. Moreover, the pereopods of P. pacifica are armed with much weaker and sparser setae than in P. japonica. [Stebbing, 1888]
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Source: Pelagic Invertebrates LifeDesk

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Ecology

Habitat

Depth range based on 668 specimens in 1 taxon.
Water temperature and chemistry ranges based on 536 samples.

Environmental ranges
  Depth range (m): 0 - 255
  Temperature range (°C): -1.437 - 10.198
  Nitrate (umol/L): 2.727 - 33.631
  Salinity (PPS): 31.593 - 33.937
  Oxygen (ml/l): 2.090 - 8.635
  Phosphate (umol/l): 0.923 - 2.858
  Silicate (umol/l): 11.561 - 67.433

Graphical representation

Depth range (m): 0 - 255

Temperature range (°C): -1.437 - 10.198

Nitrate (umol/L): 2.727 - 33.631

Salinity (PPS): 31.593 - 33.937

Oxygen (ml/l): 2.090 - 8.635

Phosphate (umol/l): 0.923 - 2.858

Silicate (umol/l): 11.561 - 67.433
 
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Dispersal

Mainly inhabits surfacial waters and only solitary specimens are found deeper than 200 m (at least in the summer). The depth of habitation of the population changes in different seasons: the crustaceans live closer to the surface in summer than they do in winter. Sometimes they form huge concentrations near the surface film of the water. [Stebbing, 1888]
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