Euphausia hanseni Zimmer, 1915
Etymology: Euphausia - brightly shining; hanseni - after H. J. Hansen
Eye: The eye is round and large in size (E. hanseni eye & rostrum). The eye diameter : carapace length is about 0.20.
Peduncle of 1st Antenna: The lappet on the 1st segment is large and strong, pointing upwards and forwards over the 2nd segment. Its distal end is bifid (E. hanseni lappet). The 2nd segment's dorsal surface is produced into two tooth-like points distally. The 3rd segment has an anteriorly-notched dorsal keel (E. hanseni,).
Rostrum: It is strong and long, reaching to or beyond the front of the eyes (E. hanseni eye & rostrum).
Carapace: The gastric area has a convex keel, which runs to and along the rostrum. Behind the eyes, the anterior margin is produced into a post-ocular spine (E. hanseni post-ocular spine). On each side of the carapace near the anterior end there is a low mound-like projection, which is produced into the hepatic spine (E. hanseni hepatic spine). There is one pair of lateral denticles set a little above the margin (E. hanseni carapace denticle).
Abdomen: The 3rd segment has a strong mid-dorsal spine. The 4th and 5th segments have small dorsal spines (E. hanseni abdominal spines). The pleuron of each of the 3rd-5th segments is not as deeply notched as in E. spinifera and E. longirostris.
Length: Adults are 19-27 mm.
Petasma: The terminal process has a heavy foot-like base, strongly arched, with a high heel. Near the rounded distal tip of the process there is a short blunt process. The proximal process is heavy and broadest near the base. The distal part expandes into a flat, deeply notched, plate. The distal margin of the more proximal half of the plate is crenated. The lateral process is hook-shaped. There is a small additional process on the median lobe (E. hanseni petasma).
Thelycum: Described by Lomakina, 1972; Guglielmo and Costanzo, 1978.
Comments: E. hanseni, E. spinifera, E. longirostris and E. tricantha form John's species group d. They all have spines on the 4th-5th abdominal segments and are similar in size. E. hanseni can be separated from the other three species by the bifid lappet on the peduncle of the 1st antenna. E. hanseni has both a post-ocular spine and a hepatic spine on the carapace, as in E. spinifera.
HORIZONTAL DISTRIBUTION
E. hanseni has been reported off the Atlantic Coast of Africa between 26°N and 33°S, off Cape Town (E. hanseni distribution).
VERTICAL DISTRIBUTION
E. hanseni is believed to live above about 300 m.
LARVAE
See the development summary (E. hanseni Table) for the stage descriptors and length in stage.
Metanauplius - undescribed
Calyptopis - (3 stages) (E. hanseni A)
Carapace:
Marginal spines - The margins of the frontal hood are smooth in C1 with the developing marginal spines of C2 visible beneath the cuticle. In C2-C3 there are small spines on the frontal plate except in the medial section above the eyes.
Postero-dorsal spine - A postero-dorsal spine is present.
Lateral denticles - A pair of denticles is present in C3.
Telson:
Postero-lateral spines - PL2 is slightly longer than PL3 in C2-C3. In C1, PL3 is longest.
Furcilia - (7 stages) (E. hanseni B), (E. hanseni C)
Eye: The eye is rounded.
Carapace:
Frontal plate / rostrum - The frontal plate is broad in F1-F2. There is a tiny rostral spine in F2, it becomes pointed like the adult by F7.
Marginal spines - There are small spines on the frontal plate except for the center section. The spines appear to persist through F5.
Postero-dorsal spines - The 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 - There is a dorsal spine on segment 3 from F2, and by F7 spines are forming on segments 4 and 5.
Pleopods: The common developmental pathway is 1' - 1"3' - 4"1' - 5".
Telson:
Postero-lateral spines - PL2 is equal to or longer than PL3 in F1. By F3, PL3 is longer.
Lateral spines - One pair of lateral spines is present.
Comments: In calyptopis stages 2-3, the absence of marginal spines in the center of the anterior margin of the carapace frontal hood may be helpful in separating larvae of E. hanseni from other species with marginal spines on the frontal hood.
In the furcilia phase, the features which separate E. hanseni from E. longirostris and E. spinifera , the other species with a mid-dorsal spine on abdomen segment 3, are: 1) the presence of marginal spines on the carapace frontal plate but absence of spines on the lateral margins, and 2) the absence of a postero-dorsal spine in F2-F7.
Development
(E. hanseni Table), development summary for the stage descriptors and length in stage.
Pictures
E. hanseni, selected stages
E. hanseni A [calyptopis 1-3]
E. hanseni B [furcilia 1-3]
E. hanseni C [furcilia 4-7]
key to larval illustrations