(M. Sars, 1857)
Description
The eye is round and medium in size [M.norvegica eye & rostrum ]. The ratio of the eye diameter and the carapace length is 0.19.
Peduncle of first antenna: the first segment with a lappet as a conspicuous, elongate, reflexed leaflet in both sexes; even so in juveniles. The distal limit of the lappet is broad and its outer angle extends laterally as a flexible tooth-like projection. Medially from this projection there are two smaller angular projections on the distal edge of the leaflet. The lappet is diagnostic for the species. The second segment has a small mid-dorsal, distal, forward-directed spine. The third segment has a similar much smaller spine [M.norvegica ped 1st ] [M.norvegica lappet ].
Carapace with front margin curving slightly downward, without any rostral process [M.norvegica dorsal head ], but with a well developed post-ocular spine [M.norvegica post-ocular spine ]. There is a single pair of carapace denticles near the edge [M.norvegica carapace denticle ].
Thoracic legs: the eighth pair of thoracic legs is rudimentary, but the seventh pair is distinctly developed, although the endopodite consists of only two elongated segments (pict)
Abdomen without dorsal spines or specific features [M.norvegica-drawing ].
Petasma: the spine-shaped process is curved. The terminal process is about 2/3 the length of the proximal process and terminates in a hook-like projection. The proximal process is cylindrical, tapering towards the end. There are four small additional processes on the median lobe [M.norvegica petasma ].
Reproduction: sexually mature at about 22 mm length (equal to about one year of age) to breed for the first time. M. norvegica may survive to 3 years, breeding each successive year (after Mauchline, 1984).
Size
Adults are 22-45 mm.
Larval stages
M.norvegica-A
M.norvegica-B
M.norvegica-C
M.norvegica-D
M.norvegica-E
M.norvegica-F
Ecology
M. norvegica is a large aggregating species and is the food of whales, seals, fish, squid, decapods and birds, particularly in coastal regions.
Depth range
Between 100 and 400 m during the day; has been caught as deep as 1500 m off W Scotland. It migrates to the surface at night in most regions, especially in the coastal waters.
Distribution in the North Sea
Central and N North Sea; occasionally in the SW North Sea when water temperatures in February-March are low (Hamond, 1971). Absent from Kattegat Mauchline, 1969) and Baltic (Mauchline, 1984).
World distribution
Restricted to the N Atlantic including the subarctic Atlantic. It extends southwards to N Africa and is present throughout much of the Mediterranean.
Remark
M. norvegica is sometimes infected with ectoparasites of Thalassomyces fagei (Ellobiopsidae) (Franqueville, 1971; De Bhaldraithe, 1973), but these seem to be absent from specimens from the NE Atlantic and the northern North Sea (Smith, 1981), as well as from Scottish inshore waters (Mauchline and Fisher, 1969).
[After Brinton et al., 1999]