Meganyctiphanes norvegica (M. Sars, 1857)
Etymology: Meganyctiphanes - large, night visible/shining; norvegica - of Norway.
Eye: The eye is round and medium in size (M. norvegica eye & rostrum). The eye diameter : carapace length is 0.19.
Peduncle of 1st Antenna: The 1st segment has an elongate, backward directed leaflet in both sexes. The distal limit of this leaflet 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 2nd segment has a small mid-dorsal, distal, forward-directed spine. The 3rd segment has a similar much smaller spine (M. norvegica,) (M. norvegica lappet).
Carapace: The front margin of the carapace curves 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).
Abdomen: There are no dorsal spines or specific features (M. norvegica).
Length: Adults are 22-45 mm.
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).
Thelycum: Described by Einarsson, 1942; Costanzo and Guglielmo, 1976a.
Comments: M. norvegica is the only species in this genus.
Ecology: M. norvegica is a large aggregating species and is the food of whales, seals, fish, squid, decapods and birds, particularly in coastal regions.
HORIZONTAL DISTRIBUTION
M. norvegica is restricted to the North Atlantic and subarctic Atlantic. It is present on the western side of Greenland and extends southward to near Cape Hatteras, 34°N along the eastern United States; it lives in the Bay of Fundy and Gulf of St. Lawrence. It occurs between Iceland and Great Britain as far northeastwards as the Barents Sea. It extends southwards to North Africa and is present throughout much of the Mediterranean (M. norvegica distribution).
VERTICAL DISTRIBUTION
M. norvegica lives between 100 and 400 m during the day and has been caught as deep as 1500 m in the Rockall Trough west of Scotland. It migrates to the surface at night in most regions, especially in the coastal habitats.
LARVAE
See the development summary (M. norvegica Table) for the stage descriptors and length in stage.
Metanauplius - (1 stage) (M. norvegica A)
Carapace:
Shape - The body is domed.
Marginal spines - There are spines along the entire margin, the spines around the frontal hood are larger than those on lateral lobes and posterior margin.
Calyptopis - (3 stages) (M. norvegica B)
Carapace:
Shape - The carapace is smoothly rounded.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - A pair of denticles is present in C3.
Telson:
Postero-lateral spines - PL3 is longer than PL2.
Furcilia (7 stages) - (M. norvegica C), (M. norvegica D), (M. norvegica E), (M. norvegica F)
Eye: The eye is round and relatively large.
Carapace:
Frontal plate / rostrum - The rostrum is truncated and almost rectangular in early stages, it is tapered in late furciliae.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - A pair of denticles is present.
Thoracic legs: There is sequential development without elongate leg (s).
Abdomen:
Mid-dorsal spines - absent
Pleopods: There is a variety of forms in F1 and F2 with different levels of pleopod development. A common developmental pathway is 3'- 3"2'- 5".
Telson:
Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - One pair of lateral spines is present.
Comments: The larvae of N. couchi and M. norvegica are very similar in the calyptopis and early furcilia phases. The following differences have been noted:
Calyptopis phase - The telson of N. couchi has 2 orange-red chromatophores together in C1 but distinct in later stages. The telson of M. norvegica is without chromatophores. (A detailed comparison of pigmentation in the two species is presented by LeRoux (1976).
The striated body of the eyestalk photohore is usually truncated anteriorly in N. couchi and pointed in M. norvegica .
Furcilia phase - The larvae of M. norvegica are larger and more heavily built than N. couchi . The difference in body length in a given stage of development increases with age. The eyes of M. norvegica are proportionally larger than the eyes of N. couchi . The carapace frontal plate is broader in M. norvegica .
Development
(M. norvegica Table), development summary for the stage descriptors and length in stage.
(M. norvegica Graph 1), a histogram of length freqency by stage, from the Clyde Sea area.
Pictures
M norvegica, selected stages
M. norvegica A [egg, nauplius, metanauplius]
M. norvegica B [calyptopis 1-3]
M. norvegica C [furcilia 1]
M. norvegica D [furcilia 2]
M. norvegica E [furcilia 3-4]
M. norvegica F [furcilia 5-6, juvenile]
key to larval illustrations