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Euphausia vallentini Stebbing, 1900

Etymology: Euphausia - brightly shining; vallentini - after Mr. Vallentin

Eye: The eye is round and large (E. vallentini eye & rostrum). The eye diameter : carapace length is 0.22.

Peduncle of 1st Antenna: The 1st segment has a large, broad and rounded process that projects horizontally above the 2nd segment. The 2nd segment ends in a low crest. The 3rd segment has a high dorsal keel (E. vallentini,).

Rostrum: It is short, not reaching the eyes' midpoint, sharply triangular, and a little longer than broad (E. vallentini eye & rostrum) (E. vallentini dorsal head).

Carapace: There is one pair of lateral denticles (E. vallentini carapace denticle ).

Abdomen: There is a short, thin, mid-dorsal process on the 3rd segment (E. vallentini abdominal spine); sometimes it is absent.

Length: Adults are 13-28 mm.

Petasma: The petasma is similar to that of E. lucens and E. frigida but easy to distinguish from them. The proximal process extends beyond the midpoint of the terminal process; its distal part gives rise to 3 irregularly shaped leaflets. The terminal process is less obviously trifurcate at its tip, the smallest branch being a minute spine-like process. The hooked lateral process has a small short finger-like process extending along the curvature of the hook (E. vallentini petasma).

Thelycum: Described by Lomakina, 1972; Guglielmo and Costanzo, 1978.

Comments: The shape and length of the rostrum together with the lappet on the 1st segment of the peduncle of the 1st antenna and the abdominal spine on the 3rd segment separates it from E. lucens and E. frigida.

ECOLOGY
E. vallentini is a food source for whales.

HORIZONTAL DISTRIBUTION
E. vallentini is a circumpolar species usually restricted to the subantarctic zone with its southern limit at 50°S-60°S. Its northern limit is usually the subtropical convergence, 40°S, but it has been recorded as far north as 32°15'S. Bradford, 1972 reported it near New Zealand, 42°26'S; 173°48.5'E (E. vallentini distribution).

VERTICAL DISTRIBUTION
E. vallentini probably occupies between about 100 m and 250 m in the day and rises near to the surface at night.

LARVAE
See the development summary (E. vallentini Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis 2-3 (3 stages) (E. vallentini A)

Carapace:
Shape - The frontal hood is rounded and curves ventrally down over the eyes in C2.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - A pair of denticles is present in C3.
Dorsal crest - A small distinct crest is present.

Telson:
Postero-lateral spines - PL3 is longer than PL2.

Furcilia - (6 stages) (E. vallentini B)

Carapace:
Frontal plate / rostrum - The frontal plate is rectangular in F1 and becomes triangular in later stages. There is usally a rostral spine from F2.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.
Dorsal keel - A distinct keel is present, less high in late stages.

Thoracic legs: There is sequential development without elongate leg (s).

Abdomen:
Mid-dorsal spines - absent
Segment 1 - The lateral projections, tergal wings, on segment 1 are connected dorsally by a tergal ridge or collar. (E. vallentini C)

Pleopods: There is some variation in form in F1-F2. The common developmental pathway is 4' - 4"1' - 5".

Telson:
Postero-lateral spines - PL3 is longer than PL2.
Lateral spines - One pair of lateral spines is present.

Comments: The larvae of E. vallentini are similar to those of E. frigida and E. lucens. E. vallentini larvae are larger than those of E. lucens , and they differ from E. frigida in the following ways: 1) carapace frontal plate less wide and square, 2) carapace dorsal crest higher and more distinct in form, and 3) tergal collar on abdomen segment 1.

Development
(E. vallentini Table), development summary for the stage descriptors and length in stage.

(Euphausia Table), developmental form frequency in 5 species of Euphausia furcilia larvae from the Southern Ocean.

Pictures
E. vallentini, selected stages
E. vallentini A [calyptopis 2-3]
E. vallentini B [furcilia 1-2]
E. vallentini C [tergal collar]
key to larval illustrations

Euphausia vallentini