Nyctiphanes couchi (Bell, 1853)
Etymology: Nyctiphanes - night visible/shining; couchi - after Professor Couch
Eye: The eye is round, large, and tends to remain black under preservation (N. couchi eye & rostrum). The eye diameter : carapace length is about 0.22.
Peduncle of 1st Antenna: The dorsal surface of the 1st segment carries a backward-directed pointed leaflet on the upper distal margin. In the male the leaflet is inclined more closely to the horizontal stalk of the segment than in the female. The 2nd segment has a multi-toothed, keel-like expansion resembling a chicken's comb but varying in shape, arising from the anterior margin; the marginal teeth on the expansion may be absent on large specimens >16 mm. In the male the 3rd segment is convex on its outer side and concave on its inner side from which a row of 3 strong plumose setae are directed forward (N. couchi,).
Rostrum: A rostrum is lacking; the frontal plate is short, and forms an obtuse triangle with raised margins (N. couchi eye & rostrum).
Carapace: There are no lateral carapace denticles (N. couchi).
Thoracic legs: Legs 1-6 (endopods) are similarly developed, and the 7th is nearly as long but consist of only 2 segments. Exopods present on legs 1-7 in males; in females 1-5. The 8th is rudimentary. In the female, paired eggs sacs are secreted adhering to the two posterior thoracic endopods (6th and 7th).
Abdomen: The 6th segment has a small mid-dorsal posterior spine (N. couchi).
Length: Adults are 12-17 mm.
Petasma: There is a spine-shaped process but the proximal and terminal processes are lacking. The curved lateral process and the median lobe are about the same length, both extending well short of the tip of the inner lobe (N. couchi petasma).
Thelycum: Described by Einarsson, 1945; Guglielmo and Costanzo, 1983.
Comments: The lappet on the 1st segment of the peduncle of the 1st antenna is inclined more sharply backwards than in the other threeNyctiphanes species (Nyctiphanes lappet).
ECOLOGY
N. couchi is a neritic species extending along the coasts of western Europe providing a food source for numerous fishes and decapods. It is believed to feed both in the water column and on the bottom where detritus is consumed (Hickling, 1925).
HORIZONTAL DISTRIBUTION
N. couchi occurs in the north-eastern Atlantic extending from 65°N along Norway southward to the British Isles, North Sea, Bay of Biscay, Northwest Africa, Western Mediterranean, but also the Adriatic and Aegean Seas (N. couchi distribution).
VERTICAL DISTRIBUTION
N. couchi is principally a shelf species and has been observed foraging on the bottom at depths of 200 m in the daytime, then surfacing at night.
LARVAE
See the development summary (N. couchi Table) for the stage descriptors and length in stage.
Metanauplius - (2 forms) (N. couchi A)
Carapace:
Shape - The carapace is smoothly rounded.
Calyptopis - (3 stages) (N. couchi B)
Carapace:
Shape - The carapace is smoothly rounded.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent
Telson:
Postero-lateral spines - PL3 is longer than PL2.
Furcilia - (6 stages) (N. couchi C), (N. couchi D), (N. couchi E)
Eye: The eye is large and round.
Carapace:
Frontal plate/rostrum - The anterior margin of the frontal plate is usually flat, it may be slightly concave in early stages.
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. The developmental pathway varies, for example 1' - 1"3' - 4"1' - 5", 2' - 2"3' - 5", and 0 - 3'- 3"2' - 5".
Telson:
Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - One pair of lateral spines is present.
Comments: N. couchi is separated geographically from the other three species of the genus, N. australis , N. capensis , and N. simplex . In two of the species, N. capensis and N. simplex , the carapace frontal plate is truncate, the anterior margin is concave, and the antero-lateral angles may be acute. In N . australis and N. couchi the anterior margin of the frontal plate is usually flat, it may be slightly indented in F1.
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 N. couchi are smaller and less heavily built than in M. norvegica. 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
(N. couchi Table), development summary for the stage descriptors and length in stage.
Pictures
N. couchi, selected stages
N. couchi A [egg, pseudometanauplius, metanauplius]
N. couchi B [calyptopis 1-3]
N. couchi C [furcilia 1]
N. couchi D [furcilia 2-3]
N. couchi E [furcilia 4-6]
key to larval illustrations