Notes
735 Records
This is one of the most widely reported species, which occurs in all oceans except the North Pacific, at latitudes ranging from 60°N to 50°S. The records from high latitudes in the Southern Ocean are anomalous and so need to be re-evaluated. They may either have arisen by misidentification of juvenile instars of symmetrica, or through specimens being mislabeled. It is often the numerically dominant species at shallow mesopelagic depths at middle latitudes (30-45°N) in the North Atlantic but declines in abundance both polewards and towards the equator. It undertakes extensive diel vertical migrations, moving up from daytime depths of 400-500m into the upper 100m at night, and is occasionally even taken in the neuston. It is the smallest member of the genus, but its rostra, the spines at the posterior dorsal corner and the tubercles at the posterior ventral corner are more extensively developed than the in other species. It produces bioluminescent secretions from glands on the anterior edge just blow the incisure, which are released into the water. It also emits light at the tips of the rostral processes, the posterior dorsal spines and the posterior ventral tubercles, but these emissions come from within the glands and not from secretions released into the water; the possible function may be to make the animal look much larger to any visually-hunting predator.
Living specimens are translucent and lightly pigmented, in contrast to its congeners, which are far more intensely pigmented.
| 44°N
|
n
|
Mean mm
|
s.d.
|
Range mm
|
|---|
| Female
|
105
|
2.77
|
0.116
|
2.56-3.04
|
|---|
| Male
|
38
|
2.40
|
0.058
|
2.24-2.52
|
|---|
| A-1
|
161
|
1.98
|
0.087
|
1.76-2.22
|
|---|
| A-2
|
200
|
1.33
|
0.058
|
1.14-1.48
|
|---|
| A-3
|
147
|
0.89
|
0.034
|
0.82-0.98
|
|---|
| Azores Front
|
n
|
Mean mm
|
s.d.
|
Range mm
|
|---|
| Female
|
63
|
2.99
|
0.097
|
2.76-3.20
|
|---|
| Male
|
9
|
2.51
|
0.136
|
2.32-2.76
|
|---|
| A-1
|
4
|
1.97
|
0.017
|
1.94-1.98
|
|---|
| A-2
|
17
|
1.31
|
0.046
|
1.26-1.36
|
|---|
| A-3
|
20
|
0.86
|
0.026
|
0.84-0.92
|
|---|
| Bermuda
|
n
|
Mean mm
|
s.d.
|
Range mm
|
|---|
| Female
|
116
|
2.96
|
0.123
|
2.60-3.20
|
|---|
| Male
|
90
|
2.48
|
0.079
|
2.28-2.64
|
|---|
| A-1
|
208
|
2.04
|
0.079
|
1.82-2.24
|
|---|
| A-2
|
217
|
1.40
|
0.051
|
1.24-1.52
|
|---|
| A-3
|
215
|
0.92
|
0.033
|
0.82-1.02
|
|---|
| Southern Ocean
|
n
|
Mean mm
|
s.d.
|
Range mm
|
|---|
| Female
|
136
|
3.00
|
0.127
|
2.72-3.24
|
|---|
| Male
|
25
|
2.55
|
0.127
|
2.24-2.80
|
|---|
| A-1
|
24
|
2.06
|
0.069
|
1.92-2.24
|
|---|
| A-2
|
16
|
1.41
|
0.063
|
1.28-1.54
|
|---|
| A-3
|
12
|
0.93
|
0.047
|
0.84-0.96
|
|---|
