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Euphausia brevis Hansen, 1905

Etymology: Euphausia - brightly shining; brevis - short

Eye: The eye is round and large in size (E. brevis eye & rostrum). The eye diameter : carapace length is about 0.20, hence the eye is smaller than in E. recurva , but similar to E. mutica and E. diomedeae.

Peduncle of 1st Antenna: The 1st segment bears a slender distally-bifurcate lappet reaching upward and forward at an angle of 60-70° with the horizontal. Occasionally the lappet is nearly vertical, though the paired acute tips may bend somewhat forward over part of the 2nd segment. The 2nd segment bears a forward-directed spine at the outer anterior margin. This spine is straight and distinctly acute. The 3rd segment has a low, poorly-defined dorsal keel (E. brevis,).

Rostrum: It is straight, acute, reaching just beyond the anterior limit of the eyes (E. brevis eye & rostrum).

Carapace: There are two pairs of lateral denticles (E. brevis carapace denticle).

Abdomen: There are no dorsal spines (E. brevis). The pleura on the 5th segment terminate acutely at their posterior-lateral limits (E. brevis acute 5th pleuron).

Length: Adults are 8-10 mm.

Petasma: The trunk of the terminal process tapers to a slender, slightly curved tip. The base of this tip is the point of origin for a slender, straight, distally-directed spine which is nearly parallel to the slender tip.

The proximal process is curved through 90°, ending as a flat, rounded oblong plate which appears to be acute in lateral view. A short obliquely-pointing tooth-like process is situated at the base of this plate (E. brevis petasma).

Thelycum: Described by Costanzo and Guglielmo , 1976a.

Comment: E. brevis is smaller than E. diomedeae, E. mutica and E. recurva. The eye is relatively smaller than in E. recurva and E. diomedeae . The distinct, straight, acute spine on the 2nd segment of the 1st antenna (E. brevis dorsal head), and the acute posterior endings to the pleura of the 5th abdominal segment (E. brevis acute 5th pleuron) are characteristic.

HORIZONTAL DISTRIBUTION
E. brevis is subtropical in all ocean basins, extending into the tropics in the Indian Ocean and on the western sides of the Atlantic and Pacific. It is lacking in the eastern boundary currents of the Pacific (E. brevis distribution).

VERTICAL DISTRIBUTION
Adults are above about 100 m at night and below 300 m in daytime.

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

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

Eye: The striated body of the eyestalk photophore is visible.

Carapace:
Shape - The frontal hood is expanded laterally and broad.
Marginal spines - The frontal hood is fringed with spines. There are three relatively long pairs interspersed along the anterior margin and 3 smaller spines between the inner pair of long spines. There may be tiny spines on the posterior margin.
Dorsal crest - There is a high dorsal crest with a pair of relatively long dorsal spines.

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

Eye: The striated body of the eyestalk photophore is visible.

Carapace:
Shape - The frontal hood is rounded antero-laterally in C1. It is curved ventrally around the eyes, and is relatively narrow, in C2-C3.
Marginal spines - The frontal hood is fringed with small spines.
Postero-dorsal spine - A postero-dorsal spine is present.
Lateral denticles - A pair of denticles is present.

Leg 1 (maxilliped) - In C1, the stout seta on the medial margin of segment 1 of the endopod is similar in length to the stout seta on the basis, unlike E. eximia and E. diomedeae . (Euphausia larval maxilliped)

Telson:
Shape - The width of the telson between the lateral spines and between the first pair of postero-lateral spines is nearly equal.
Postero-lateral spines - PL2 is longer than PL3.

Furcilia - (6 stages) (E. brevis C), (E. brevis D), (E. brevis E)

Eye: The eye is distinctive. The eyestalk photophore is relatively very large and the ommatidia develop first in the upper portion of the eye. (Euphausia larval eye)

Carapace:
Frontal plate / rostrum - The frontal plate is rectangular in early furcilia and becomes broadly triangular in late furcilia. There is a tiny rostral spine by F3.
Marginal spines - The frontal plate is fringed with spines that may be realtively coarse, the spines persist through F5.
Postero-dorsal spines - A spine is present in F1 only.
Lateral denticles - A pair of denticles is present.

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

Abdomen:
Mid-dorsal spines - absent

Pleopods: The common developmental pathway is 1' - 1"4' - 5".

Telson:
Postero-lateral spines - PL2 is longer than PL3 through F3.
Lateral spines - One pair of lateral spines is present.

Comments: Larvae of Euphausia species group 1A (Brinton, 1975), E. brevis, E. diomedeae, E. mutica, E. recurva, E. eximia and E. krohni are very similar. E. americana is undescribed. E. brevis is the easiest of the species to recognize.

See the closely related species E. eximia for a lateral view of the development of the second antenna, thoracic legs, and pleopods.

The narrow frontal hood distinguishes the calyptopis stages and the distinctive eye is characteristic of the species in the furcilia phase (Euphausia larval eye).

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

Pictures
E. brevis, selected stages
E. brevis A [metanauplius]
E. brevis B [calyptopis 1-3]
E. brevis C [furcilia 1-2]
E. brevis D [furcilia 3-4]
E. brevis E [furcilia 5-6]
Euphausia larval eye
Euphausia larval maxilliped [species characters]
key to larval illustrations

Euphausia brevis