Calyptommini W. M. Tattersall 1909

Key to genera and species of the tribe Calyptommini

Distribution data modified and updated from Petryashov (2014).

Mysidae: Erythropinae with eyeplate showing no distinct median cleft, plate mainly formed by a transverse median bridge, eyes rudimentary or absent. Smooth outer margin of antennal scale ending in a tooth. Pleopods uniramous, reduced to sparsely setose rods or plates in both sexes. Telson entire, its lateral margins mostly smooth, terminal portions with spines................... Tribus Calyptommini W.M. Tattersall, 1909 (Arctic and Atlantic oceans, Mediterranean, 81° N to 17 ° S, depth 27–5460 m, mainly bathybenthic) …..........................................................................................................…. 1

1. Lateral portions of eyeplate with anteriorly directed, conical lobes; telson about as long as wide; appendix masculina strong, with large brush of setae............................................................................... Abyssomysis cornuta gen. et sp. nov. (abyssal plain of the Angola Basin, depth 5430–5460 m)

– Eyeplate without antero-lateral protrusions; telson length at least twice the width at basis; appendix masculina reduced, without brush of setae....................................................................................... 2

2. Anterior margin of eyeplate in the middle with a deep, rounded depression; antennal scale short, not extending beyond antennular trunk; telson subtriangular, terminally rounded................................................................... monotypic genus Calyptomma W.M. Tattersall, 1909, with species Calyptomma puritani W.M. Tattersall, 1909 (Mediterranean, depth 600–1860 m)

– Anterior margin of eyeplate without or with a very small median depression; antennal scale clearly extending beyond antennular trunk; telson trapezoid, terminally rounded. Genus Michthyops W.M. Tattersall, 1911.................................................................................................................................. 3

3. Eyeplate completely or for the most part covered by flattened anterior edge of carapace; length of antennal scale exceeds seven times width; terminal margin of telson with 3–4 pairs of robust spines............................................................................................................................... Michthyops arcticus Petryashov, 1993 (Arctic: Canadian basin, north of Laptev Sea, depth 1079–3550 m)

– Eyeplate covered by anterior edge of carapace for less than half its length; length of antennal scale less than seven times width............................................................................................................... 4

4. Telson length less than 2.5 times maximum width near basis; terminal margin of telson with three pairs of robust spines......................................................................................................................................................... Michthyops parvus (Vanhöffen, 1897) (N-Atlantic, Arctic, depth 183–2900 m)

– Telson length exceeds 2.5 times maximum width near basis; terminal margin of telson with 4–8 (mostly 5–6) pairs of robust spines.............................................................................................................................. Michthyops theeli (Ohlin, 1901) (Circumarctic, Greenland Sea, depth 27–2245 m)