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Characteristics, distribution and ecology
Taxonomische classification
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Skogsberg, 1920

Diagnosis
Carapace globular with the ventral surface slightly flattened (G. muelleri Habitus 1, G. muelleri Habitus 2). Its maximum length of 20mm makes it easily the largest species of ostracod to be found regularly in the North Atlantic. Live and freshly preserved specimens are translucent orange-red. Large naupliar eyes with mirror reflectors which are circular in the vertical plane and parabolic in the horizontal (G. muelleri 1). This has the effect of focusing light onto a small patch of retinal material at the focal centre of the parabolic section (Land, 1978). When freshly caught, undamaged specimens float, but if kept for a few hours they will regain neutral buoyancy. The rostrum and its incisure are relatively small. The opening between the valves extends less than three quarters of their total length (G. muelleri Habitus 3). The setation around the rostrum and the incisure is characteristic (G. muelleri 1). The animals can extend their limbs through the restricted gape, possibly by deforming the shape of the carapace. Descriptions of the swimming by these animals being unstable are inaccurate; they swim strongly and steadily (Davenport, 1990). They are active carnivores, feeding on chaetognaths, mysids and medusae.
Their shape and general appearance makes them instantly identifiable. Normally, they are restricted to depths 700-2500m but their maximum abundance is around 1000- 1500m.

Remarks
This characteristic species cannot be mistaken for any other planktonic ostracod apart from is congener G. dracontovalis (Gigantocypris dracontovalis). It is quickly distinguishable, even from this species, by its larger size, the setation around the rostrum, its more intense colouration and shallower depth range.

Distribution
Recorded from 60°N-53°S in the Atlantic but is more abundant >40°. Its bathymetric range is deep mesopelagic to bathypelagic 800-2000m. There is evidence that it undergoes an ontogenetic migration since juveniles tend to be caught at shallower depths than the adults. 1, 2, 3, 4 (R.R.S. Discovery Map).

Type specimens
None designated; status of original material uncertain.

Type locality
48°24'N, 36°53'W. Depth: 1500m wire out (i.e., ca.750m).

Gigantocypris muelleri