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(Brady, 1880)

Description
An unmistakable species. Carapace with both rostra extended into long curving processes, left slightly longer than the right. The carapace carrying spines on both valves at the postero-dorsal corner and tubercles at the posteroventral corners [C.imbricata-fem-lat; C.imbricata-male-lat; C.imbricata-fem-vent; C.imbricata-male-vent].
The posterior margin is almost straight, forming an oblique angle with the dorsal margin. Ventral margin tapers anteriorly, but is angled at about three-quarters length, where the carapace height is maximum. The anterior ventral margin beneath the incisure is spinose.
The whole surface of the carapace is covered with a clear sculptured pattern of rectangles; in the ventral region the vertical ridges are more outstanding, but in the dorsal region it is the horizontal bars which are the more strongly developed.
In both sexes, the capitulum of the frontal organ is covered with quite long spines [C.imbricata-1; C.imbricata-3]. Male first antenna "e" seta armature a double row of stout broad spines set almost at right angles to the seta [C.imbricata-4].

Size
Female 2.6-3.0 mm, male 2.28-2.64 mm carapace length.

Depth range
Mesopelagic depths of 400-700 m.

Distribution in the North Sea
Northern North Sea.

World distribution
All oceans. From 65°N-55°S in the Atlantic, where it may also occur >60°N according to Poulsen (1977).

Remarks
According to recent taxonomic revision, the species imbricata is placed in the genus Conchoecissima (M.V. Angel, pers. com.). However, for technical reasons, the former generic name Conchoecia had to be maintained in the multimedia files.
C. imbricata is a strong diel vertical migrant, and it is also the species that most readily shows the ability to modify its sinking rate. The carapace projections (rostra, posterior and ventral corners) are all associated with retained bioluminescence - possibly a mechanism whereby an individual can make itself look bigger to a visually-hunting predator. Müller (1906) placed all the species with such modification of the carapace in his imbricata group (i.e., ametra, squamosa, symmetrica and plinthina). All the species of this natural grouping have been taken in the North Atlantic, except for C. squamosa, which is a Southern Ocean endemic. However, only C. ametra and C. imbricata have been taken at latitudes >40°.

[After Angel, 2000]

Conchoecissa imbricata