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Claus, 1874

Diagnosis
Carapace is similar in shape to C. hyalophyllum (Conchoecia hyalophyllum). In both sexes, the height : length ratio is Müller. In the female, there is a marked anterior taper (C. magna Habitus 1). In ventral view the rostra are spade-ended without taper (C. magna Habitus 2, C. magna Habitus 4), the antero-ventral edge beneath the incisure is sharp edged, and the breadth : length ratio is about or > 40%. The right symmetrical gland opening at the postero-ventral corner is smaller than in C. subarcuata (Conchoecia subarcuata). Left asymmetrical gland opens just anterior to the posterior end of the hinge. Sculpture usually faint, but occasional specimens have a clear concentric pattern of striae over the whole carapace.
Female, frontal organ similar to that of C. hyalophyllum (Conchoecia hyalophyllum), but capitulum is relatively longer with a longer curved terminal point (C. magna 1).
Male, frontal organ capitulum spinose, down-turned with a rounded end (C. magna 3). First antenna, "a" seta slightly longer than second segment, "c" seta short, subequal "b" and "d" setae just shorter than "e" seta, "e" seta armature 13-16 pairs of short stubby spines, replaced proximally by a further 14-17 alternating slimmer spines (C. magna 4). Second antenna endopodite "b" seta with tuft of long hairs (C. magna 5).

Remarks
Similar to C. hyalophyllum (Conchoecia hyalophyllum), but distinguished by its greater size and spade-shape of rostra in ventral aspect. Male also quite similar to C. parthenoda (Conchoecia parthenoda) but left asymmetrical gland opens adjacent to the postero-ventral corner in this species but well anteriorly in the latter. Its relatively large breadth : length ratio and the relatively small right asymmetrical gland separates it from C. subarcuata (Conchoecia subarcuata).
Sylvester-Bradley and Iles, 1956 designated C. magna as the type species for the Dana's (Dana, 1849) genus Conchoecia. Dana's descriptions were too inadequate to attribute any present species to them. Claus, 1891 retained the genus Conchoecia for all the species he originally ascribed to the magna group. Poulsen, 1973 included C. magna , C. macrocheira (Conchoecia macrocheira), C. lophura (Conchoecia lophura), C. hyalophyllum (Conchoecia hyalophyllum), C. subarcuata (Conchoecia subarcuata) and C. parvidentata in the genus, of which all but the last occur commonly in the Northeast Atlantic.

Distribution
Recorded from all oceans, 53°N-55°S in Atlantic. A strong diel vertical migrant which ranges from 100-800m. 1, 2 (R.R.S. Discovery Map).

Type specimens
None designated; status of original material uncertain.

Type locality
Original material was collected in the Mediterranean Sea in the vicinity of Naples and Messina.

Conchoecia magna