It is interesting to note the great abundance of specimens in almost all samples from the hydrothermal vent field Rainbow (Mid-Atlantic Ridge). Indeed, a total of 700 specimens were caught in the different traps (KHRIPOUNOFF et al. 2001). They were regularly present from September to January and more markedly in October and November at different distances from the vents. They were always absent in traps from February to June, except for traps laid far off vent sites (2 km). Curiously, all the specimens were juveniles. Chemical analysis of the composition of particles from the stomach content has been done by EDS X-ray microanalysis. A comparison between T. parva specimens and specimens of the related species T. gregaria indicate that probably the T. parva population is more or less linked with the particle flux. Indeed, a peak of the Fe element is obvious and might be related with the high concentration of iron (7%) in the vent particles (KHRIPOUNOFF et al. 2001) that does not exist in T. gregaria (unpublished data). However, studies of T. parva specimens caught far from the vents have yet to verify this hypothesis. Curiously, there were no euphausiaceans in traps laid in the South Atlantic (Gulf of Guinea) and in the Pacific (East Pacific Rise: 13°N) (M. Segonzac, pers. comm.).

depth in m: 300-500; horizontal distribution: subtropical part of the Atlantic Ocean, mesopelagic

European waters (ERMS scope), Gulf of Maine, Mediterranean Sea

It is a rare meso-bathypelagic species. In the Atlantic, it has been recorded off Portugal and Africa, from the latitude of Gibraltar to near Cap Town; on the western side, it is mentioned near the Bermuda Islands. In the Pacific, it is known in scattered areas: east of south Japan, off California and east of New Zealand. In the Indian Ocean, it exists west of Sumatra. Mid-Atlantic Ridge: Rainbow.

Rostrum acute, ending beyond the eyes. Eyes large, with a transverse constriction between two lobes, the upper one being smaller than the lower. Carapace with a lateral small denticle on its inferior margin, posterior to its mid-point. Thoracopods almost uniform in structure, although the second pair is elongated; their setae are provided with setules visible only at high magnifications. The eighth pair is rudimentary. The seventh pair has well developed exopodites; endopodites are absent in males and short in females. Sixth abdominal segment shorter than the sum of lengths of the two preceding segments. Photophores are present on the eye stalks, at the bases of the thoracopods 3 and 7 and on the mid ventral part of abdominal segments 1-4.

Max. length 9-10.5 mm.

Depth range based on 169 specimens in 1 taxon.
Water temperature and chemistry ranges based on 168 samples.

Environmental ranges
  Depth range (m): 50.5 - 5422.5
  Temperature range (°C): 2.446 - 19.723
  Nitrate (umol/L): 0.279 - 34.674
  Salinity (PPS): 34.888 - 36.485
  Oxygen (ml/l): 1.958 - 6.060
  Phosphate (umol/l): 0.077 - 2.111
  Silicate (umol/l): 1.150 - 47.734

Graphical representation

Depth range (m): 50.5 - 5422.5

Temperature range (°C): 2.446 - 19.723

Nitrate (umol/L): 0.279 - 34.674

Salinity (PPS): 34.888 - 36.485

Oxygen (ml/l): 1.958 - 6.060

Phosphate (umol/l): 0.077 - 2.111

Silicate (umol/l): 1.150 - 47.734
 
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