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Euphausia sanzoi Torelli, 1934

Etymology: Euphausia - brightly shining; sanzoi - after Mr. Sanzo

Eye: The eye is round and large (E. sanzoi eye & rostrum). The eye diameter : carapace length is about 0.24.

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 rounded distal cover extending forward over part of the third segment (E. sanzoi, ). In E. sanzoi the 3rd segment has an anteriorly-notched dorsal keel as in E. gibboides, whereas in E. fallax this keel has no acute notch and is more rounded, both anteriorly and posteriorly.

Rostrum: It is acute or pointed in lateral view, curving slightly upward (at an angle of ca. 3°) as it extends forward just beyond the midline of the eye (E. sanzoi eye & rostrum).

Carapace: The gastric region is domed, with a vestige of a bump (more prominent in the juvenile) just posterior to and equal in height to the more rounded dorsal crest on the gastric dome. Detail of this shape is characteristic of E. sanzoi . There is one pair of lateral denticles (E. sanzoi carapace denticle).

Abdomen: There is a small, slender, mid-dorsal posterior spine on the third segment (E. sanzoi abdominal spine).

Length: Adults are 15-18 mm.

Petasma: The terminal process divides into two finger-like parts distally: the more distal one is curved, the other is shorter and more blunt. The median lobe has two triangular processes halfway along its inner edge below the lateral process, extending towards the inner lobe. The outer (setiferous) lobe has 7 setae terminally and 1-3 on the outer basal edge (E. sanzoi petasma).

Thelycum: Described by Guglielmo and Costanzo, 1978.

Comments: E sanzoi, together with E. gibboides and E. fallax forms an "E. gibboides group" of closely related species. E. sanzoi and E. fallax have similar distributions, occuring only in the tropical Indo-western Pacific, while E. gibboides lives to the north and east of these species in the Pacific and also occurs in the Atlantic. The shapes of the keel on the third segment of the peduncle of the 1st antenna and the petasma processes are useful characters.

HORIZONTAL DISTRIBUTION
E. sanzoi inhabits the western Indian Ocean, from the Red Sea and Arabian Sea to Madagascar, basins of the East Indian Archipelago, and waters near the Philippines and northeast of Australia (E. sanzoi distribution).

VERTICAL DISTRIBUTION
Many adults were present in a nighttime surface sample from near southern Luzon in the Philippines. The daytime distribution is not known.

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

Metanauplius - undescribed

Calyptopis - (3 stages) (E. sanzoi A)

Carapace:
Shape - The frontal hood is rounded laterally in C1 and curves around the eyes in C2-C3.
Marginal spines - The frontal hood is fringed with marginal spines.
Postero-dorsal spine - A postero-dorsal spine is present.
Lateral denticles - A pair of denticles is present in C3.

Mandible: There is a lateral tubercle on each mandible, proximal to the antero-lateral process. (E. sanzoi E)

Telson:
Postero-lateral spines - PL2 is longer than PL3 in C2-C3, and equal or very slightly longer in C1.

Furcilia - (6 stages) (E. sanzoi B), (E. sanzoi C), (E. sanzoi D)

Eye: The faceted portion has a rounded rectangular contour in lateral view with the pigment in 3 zones. The eye becomes rounded in mid-late furcilia stages.

Carapace:
Frontal plate / rostrum - The frontal plate is rectangular in F1 and becomes broadly triangular in late furcilia. There is a small rostral spine by F3.
Marginal spines - There are small spines on the frontal plate in F1-F3 and sometimes a few tiny spines in F4-F5.
Postero-dorsal spines - A postero-dorsal spine is present in F1 only.
Lateral denticles - A pair of denticles is present.
Dorsal keel - A distinct dorsal keel is present.

Mandible: There is a small lateral tubercle on each mandible, proximal to the antero-lateral process in F1. It may be present in F2, but disappears in F3. (E. sanzoi E)

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, or equal to, PL3 in F1-F4.
Lateral spines - One pair of lateral spines is present.

Comments: E. sanzoi , with E. fallax and E. gibboides , forms the "Euphausia gibboides group" of related species. The larvae of E. sanzoi and E. fallax may be very similar, especially in furcilia stages. Some features which may be useful to separate the larvae of E. fallax and E. sanzoi are:

Calyptopis
Carapace -
The frontal hood is wider in E. fallax .
The postero-dorsal spine is larger and tilted dorsally in E. fallax .

Furcilia
Eye - The eye is rectangular in E. fallax and rounder in E. sanzoi .
Carapace -
The postero-dorsal spine of F1 is longer and stronger in E. fallax .
The dorsal keel is larger and more distinct in E. sanzoi , especially in late furcilia.
Telson-
The lateral spines are situated more distally in E. fallax.

Photophore on abdomen segment 3-
The photophore is pigmented in E. fallax F4-F6 and may or may not be pigmented in E. sanzoi F6.

E. fallax and E. sanzoi may be very difficult to identify in F2-F5 and may be referrable only to the species pair.

E. sanzoi and E. fallax may also be very similar to the E. brevis -E. diomedeae -E. mutica -E. recurva group of related species. They may be separated by the following features: 1) mandible with lateral tubercle in calyptopis and early furcilia stages, and 2) postero-lateral spine 3 of telson with inner margin bare except for a few distal spinules in F3 and following stages.

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

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

Euphausia sanzoi