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Pseudeuphausia latifrons (G.O. Sars, 1883)

Etymology: Pseudeuphausia - false Euphausia ; latifrons - with wide forehead

Eye: The eye is large in size (P. latifrons eye & rostrum). The eye diameter : carapace length is about 0.20.

Peduncle of 1st Antenna: The 1st segment has a low, pectinate, anteriorly-directed fringe or lappet(P. latifrons,). The 2nd segment has 7-10 distal setae which are directed anteriorly, adhering closely to the 3rd segment, with the tips converging mid-dorsally as a bundle. (See also the generic diagnosis in Higher Taxa.)

Rostrum: A rostrum is lacking but the frontal plate projects anteriorly, beyond the midpoint of the eye, as a rectangle, the anterior margin of which is somewhat concave or medially depressed (P. latifrons dorsal head).

Carapace: There is a small denticle near the posterior lateral limit of the carapace (P. latifrons).

Thoracic legs: Legs 1-5 are similar. The three distal segments of the 6th thoracic leg (endopod) of the male are, together, scarcely more than half as long as those segments of the 5th leg. In the female the 6th leg is only half as long as the 5th, but the 3rd and 4th joints form a semi-circle so as to support an ovisac (P. latifrons male vs. female), while the 3 terminal joints are extremely short.

Abdomen: The 6th segment of the abdomen has a short mid-dorsal posterior denticle.

Petasma: The distal end of the inner lobe is triangular, not digitate, and there are 3 or 4 spine-shaped processes on it. Those on the outer side are similar in size to the ones on the inner side and are scarcely curved. The median, auxiliary and setiferous lobes are as in the generic description (P. latifrons petasma).

Thelycum: Described by Guglielmo and Costanzo, 1983.

Length: Adults are 7-12 mm in most regions, but reach 16 mm in the Persian Gulf.

Comments: Weigmann (1971) suggested that the extreme elongation of the median lobe's leaf-shaped plate and of the digitiform setiferous lobe in large Persian Gulf specimens might be evidence of genetic variation in different populations. A key character used to separate the two species of this genus is the absence of a mandibular palp in adult P. sinica (P. latifrons vs. P. sinica).

HORIZONTAL DISTRIBUTION
The range extends from the Red Sea, Persian Gulf and Arabian Sea eastward to the Bay of Bengal, Gulf of Thailand, East Indian Archipelago, Philippines and Islands of the Tropical Western Pacific as far east as the Samoa Is., 170°W (P. latifrons distribution).

VERTICAL DISTRIBUTION
P. latifrons is neritic, being particularly abundant in gulfs of less than 100 m depths, but it disperses over deeper basins.

LARVAE
See the development summary (P. latifrons Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis 3 (3 stages) (P. latifrons A)

Carapace:
Shape - The carapace is smoothly rounded, it projects in a hood-like manner over the first abdominal segment.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent

Telson:
Postero-lateral spines - PL3 is longer than PL2.

Furcilia - (? 5 stages) (P. latifrons B)

Eye: The eye is round.

Carapace:
Frontal plate / rostrum - The frontal plate is truncate and concave. It may be deeply emarginate and angular in the center. The antero-lateral angles are acute and may be prominent and spine-like.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - A pair of denticles is present.

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

Abdomen:
Mid-dorsal spines - absent

Pleopods: A variety of forms with different levels of pleopod development in F2 and F3 have been reported. The common developmental pathways are not known.

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

Comments: The larvae of P. latifrons maybe similar to those of N. australis . In living larvae the species maybe separated by the presence of red chromatophores on the telson of N. australis , close together in C1 but distinct in later stages. P. latifrons does not have chromatophores on the telson. In calyptopis 3 of P. latifrons , the carapace projects posteriorly in a hood-like manner over the first abdominal segment. In N. australis the posterior carapace margin appears about equal in length to the lateral margins. In the furcilia phase, the frontal plate of the carapace is deeply indented medially in mid-late furcilia of P. latifrons , and the antero-lateral angles are prominent. In N. australis these features are less exaggerated.

Development
(P. latifrons Table), development summary for the stage descriptors and length in stage.

Pictures
P. latifrons, selected stages
P. latifrons A [calyptopis 3]
P. latifrons B [furcilia 1-3, 5]
key to larval illustrations

Pseudeuphausia latifrons