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Euphausia frigida Hansen, 1911

Etymology: Euphausia - brightly shining; frigida - cold

Eye: The eye is round and large (E. frigida eye & rostrum). The eye diameter : carapace length is about 0.28 (male) and 0.22 (female).

Peduncle of 1st Antenna: The 1st segment has a small, triangular, somewhat rounded lobe that projects forwards from the inner distal corner. The 3rd segment has a strong dorsal keel (E. frigida,).

Rostrum: There is no rostrum (E. frigida eye & rostrum). The frontal plate is very short and triangular with a small acute tip (E. frigida dorsal head).

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

Abdomen: There are no dorsal spines or specific features (E. frigida).

Length: Adults are 11-24 mm.

Petasma: The terminal process has the distal end cleft into inner and outer branches which are flattened; the inner branch is divided into unequal lobes, the smaller of which is finely serrated on one edge. The proximal process has a heel near the base and ends as a pair of thin membranous expansions at the base of which there is an obliquely directed curved blade. The lateral process curves distally and has a small tooth on the outside of the bend (E. frigida petasma).

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


Comments: E. frigida is similar to E. lucens but can be separated by the lappet (E. frigida lappet) and the shape of the frontal plate (E. frigida dorsal head).

ECOLOGY
E. frigida aggregates and is a food source for whales.

HORIZONTAL DISTRIBUTION
E. frigida is a circumpolar species in the zone 45°-60°S, with its distribution centered near the Antarctic Convergence (E. frigida distribution).

VERTICAL DISTRIBUTION
E. frigida is found above depths of about 300 m.

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

Metanauplius - (1 stage) (E. frigida A)

Carapace:
Shape - The body is domed. The frontal hood is rounded laterally.
Marginal spines - The frontal plate is fringed with small marginal spines. There are longer pairs interspersed on the anterior margin. There are small spines on the lateral lobes and on the posterior margin.
Dorsal crest - There is a dorsal prominence without spines.

Calyptopis - (3 stages) (E. frigida B)

Carapace:
Shape - The carapace is rounded and the frontal hood curves down ventrally covering the eyes in front and on either side. The posterior margin is slightly pointed in C3.
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 - (6 stages) (E. frigida C), (E. frigida D)

Eye: The eye is rounded.

Carapace:
Frontal plate / rostrum - The frontal plate is rectangular in F1, and becomes triangular and acute in later stages. There is usually a small rostral spine by F2.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.
Dorsal keel - There may be a small keel in early stages.

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

Abdomen:
Mid-dorsal spines - absent
Segment 1 - Segment 1 is with or without small lateral projections, tergal wings, in F1. The tergal wings are present from F2 but are not connected dorsally by a tergal ridge or collar. (E. frigida E)

Pleopods: There may be some variety in forms in F1-F2 with different levels of pleopod, development, 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. frigida are similar to those of E. lucens and E. vallentini . E. frigida larvae are larger than those of E. lucens and differ from E. vallentini in the following ways: 1) carapace frontal plate wider and more square, 2) carapace dorsal keel less conspicuous, and 3) abdomen segment 1 with tergal wings unconnected by a tergal collar.

Development
(E. frigida 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. frigida, selected stages
E. frigida A [nauplius, metanauplius]
E. frigida B [calyptopis 1-3]
E. frigida C [furcilia 1-2]
E. frigida D [furcilia 4]
E. frigida E [tergal wings]
key to larval illustrations

Euphausia frigida