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Euphausia gibboides Ortmann, 1893

Etymology: Euphausia - brightly shining; gibboides - bent, hunched-like

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

Peduncle of 1st Antenna: Processes on the first two segments are characteristic of all three species of the "E. gibboides species group": the 1st segment has a simple upward- and forward-directed, pointed lappet; the 2nd segment has a distal dorsal-lateral cover extending forward over part of the 3rd segment (E. gibboides,). In E. gibboides (and E. sanzoi) the 3rd segment has a high dorsal keel with the distal edge produced dorsally as a notch (smoothly rounded in E. fallax).

Rostrum: It is long extending beyond midpoint of the eyes, sharply pointed, curving barely upward (E. gibboides eye & rostrum) (E. gibboides head photo 2).

Carapace: The gastric region is conspicuously domed, with vestige of a secondary hump behind the smooth crest of the dome. There is one pair of lateral denticles (E. gibboides carapace denticle).

Abdomen: There is a slender, mid-dorsal posterior spine on the 3rd segment (E. gibboides abdominal spine) (E. gibboides photo).

Length: Adults are large, 16-26 mm.

Petasma: The proximal process is long, slender, and curved. The process expands somewhat and then tapers gradually to a little before the end. The terminal process is a broad, oblong, distally rounded plate, with a long, slender tooth at its base. On the inner side of the base of the median lobe is a small, conical tubercle. The lateral process is thick at the base and considerably curved. The setiferous lobe is broad and moderately setose on the distal part of the inner margin and on the terminal margin (E. gibboides petasma).

Thelycum: Described by Guglielmo and Costanzo, 1978.

Comments: "Gibboides" refers to the typically gibbous or crescent-like abdominal curvature, indistinctly hunched around the spined 3rd segment.

E. gibboides, together with E sanzoi and E. fallax forms an "E. gibboides group" of closely related species.

It is a large species and grossly similar to E. eximia , with which E. gibboides co-occurs in much of the eastern Pacific.

ECOLOGY
E. gibboides is adapted to cool subsurface layers in the productive boundary areas of the subtropical Atlantic and Pacific.

HORIZONTAL DISTRIBUTION
E. gibboides occurs in zones of transition between temperate and tropical waters, 40°N-40°S, of the Atlantic and Pacific, not including the most oligotrophic central areas. It is present around the boundaries of the Atlantic, but in the Pacific is limited to the North Pacific Drift, the California and Peru-Chile currents and the South Equatorial Current, to mid-ocean (E. gibboides distribution). It is a large species and grossly similar to E. eximia , with which E. gibboides co-occurs in much of the eastern Pacific.

VERTICAL DISTRIBUTION
All life stages live in and below the thermocline. Adults migrate down to 300-400 m by day.

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

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

Carapace:
Shape - The frontal hood is expanded laterally and wide.
Marginal spines - The frontal hood is fringed with small spines. There are longer pairs of spines interspersed along the anterior margin.
Dorsal crest - There is a prominent pointed crest without dorsal spines.

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

Carapace:
Shape - The frontal hood is wide in C1-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 in C3.

Mandible: There is a small lateral tubercle on each mandible, proximal to the antero-lateral process. It is well formed in C1 and rudimentary by C3.

Telson:
Shape - The telson is relatively wide.
Postero-lateral spines - PL2 is longer than PL3 in C2-C3, PL3 may be slightly longer in C1.

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

Eye: The eye is large. The pigment develops in 3 zones and the cornea is indented giving a 3-lobed appearance.

Carapace:
Frontal plate / rostrum - The frontal plate is wide and rectangular in F1, rounded in mid-furcilia stages and broadly triangular by F6. There may be a tiny rostral spine in F6.
Marginal spines - The frontal plate is fringed with small spines in F1-F2.
Postero-dorsal spines - A postero-dorsal 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"3' - 4"1' - 5".

Telson:
Postero-lateral spines - PL2 is longer than PL3 in F1-F3. From F3, there are small distal spinules only on the inner margin of PL3.
Lateral spines - One pair of lateral spines is present.

Comments: The very broad carapace frontal hood in the calyptopis stages and contour of the eye in the furcilia stages are characteristic of the species. The lateral mandible tubercle is characteristic of the calyptopis stages of the "E. gibboides group" including E. fallax and E. sanzoi .

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

Pictures
E. gibboides, selected stages
E. gibboides A [egg, nauplius, metanauplius]
E. gibboides B [calyptopis 1-3]
E. gibboides C [furcilia 1-2]
E. gibboides D [furcilia 3-4]
E. gibboides E [furcilia 5-6]
key to larval illustrations

Euphausia gibboides