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Euphausia longirostris Hansen, 1908

Etymology: Euphausia - brightly shining; longirostris - with long rostrum

Eye: The eye is round and large (E. longirostris eye & rostrum). The eye diameter : carapace length is about 0.23.

Peduncle of 1st Antenna: The lappet is basically bifid, but the outer spine usually carries a third smaller spine on its outer margin. The 2nd segment has a strong spine at its distal end that extends over the 3rd segment to less than the midpoint. There is a dorsal keel on the 3rd segment (E. longirostris,) (E. longirostris lappet).

Rostrum: It is very long, reaching almost to the distal end of the 1st segment of the peduncle of the 1st antenna (E. longirostris eye & rostrum).

Carapace: There is a strong median keel with a pronounced crest in the gastric region. There is a strong post-ocular spine behind the eye (E. longirostris ). The carapace is without hepatic spines but there are low mounds present on either side. There is a lateral denticle above an incision in the lower edge of each side of the carapace (E. longirostris carapace spine).

Abdomen: The pleura of each of the 3rd-5th segments are strongly notched (incised) posteriorly (E. longirostris, ). Mid-dorsally the 1st and 2nd segments are produced posteriorly into small, wide, rounded projections. The 3rd segment has a strong dorsal spine. Segments 2, 4 and 5 have small dorsal spines (E. longirostris).

Length: Adults are 20-34 mm.

Petasma: The terminal process is bent inward above the heavy base. There is a digitiform process at the distal end. The proximal process is bent inward and ends in a large membranous expansion which curls backward and upward. The lateral process is hooked and carries a small additional process on the curve. There is a small additional process on the median lobe (E. longirostris petasma).

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

Comments: E. longirostris, E. spinifera, E. hanseni and E. tricantha form John's species group d. They all have spines on the 4th-5th abdominal segments and are similar in body size. E. longirostris can be separated from the other three by the trifid lappet, and the combination of strongly notched pleura on abdominal segments 3-5, lack of hepatic spines, and very elongate rostrum.

HORIZONTAL DISTRIBUTION
E. longirostris is a subantarctic species occurring between about 30°S and 55°S. It has not been reported south of the Antarctic Convergence, but does occur north of the Subtropical Convergence (E. longirostris distribution).

VERTICAL DISTRIBUTION
E. longirostris is believed to live above 300 m.

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

Metanauplius - undescribed

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

Carapace:
Shape - The frontal hood is wide and the body is domed.
Marginal spines - The entire margin of the carapace is fringed with small spines.
Postero-dorsal spine - A postero-dorsal spine is present.
Lateral denticles - absent
Dorsal crest - There is a high, conical dorsal crest without spines.

Abdomen: The postero-lateral margins of the pleura have small spines in C3.

Telson:
Shape - The telson is wide distally.
Postero-lateral spines - PL2 is longer than PL3.

Furcilia - (7 stages) (E. longirostris B), (E. longirostris C), (E. longirostris D )

Carapace:
Frontal plate / rostrum - The frontal plate is wide and rectangular with rounded corners. There is a rostal spine in F3 which lengthens in late furcilia stages.
Marginal spines - The rostral plate is fringed with small spines. There are also small spines on the lateral margins between the antero-lateral spines and the lateral denticles.
Postero-dorsal spines - A postero-dorsal spine is present throughout the furcilia phase.
Lateral denticles - A pair of denticles is present.
Dorsal keel - A distinct keel is present.

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

Abdomen:
Mid-dorsal spines - There is a dorsal spine on segment 3 from F1, segments 4 and 5 are without spines.
Marginal spines - There are small marginal spines on the postero-lateral margins of the pleura in F1-F3.

Pleopods: The common developmental pathway is 1' - 1"3' - 4"1' - 5".

Telson:
Postero-lateral spines - PL2 is longer than PL3 through F3.
Lateral spines - One pair of lateral spines is present through F5, there may be 2 pairs in F6, and 3 pairs in F7.

Comments: The larvae are relatively large. The form of the carapace in C2-C3 with high conical dorsal crest and fringe of marginal spines distinguishes the species.

In furcilia stages the larvae of E. longirostris may be distinguished from other species with a mid-dorsal spine on abdomen segment 3 by 1) the position of the marginal spines on the lateral carapace margins, 2) the very strong postero-dorsal carapace spine in all stages, and 3) the marginal spines on the abdominal pleura.

Development
(E. longirostris 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. longirostris [selected stages]
E. longirostris A [calyptopis 2-3]
E. longirostris B [furcilia 1-2]
E. longirostris C [furcilia 3-4]
E. longirostris D [furcilia 5-7]
E. longirostris E [juvenile]
key to larval illustrations

Euphausia longirostris