Stylocheiron robustum Brinton, 1962

Etymology: Stylocheiron - a column/hand; robustum - strong, robust

Eye: The width of the upper lobe is approximately equal to that of the widest part of the lower lobe, (~0.8:1.0) (S. robustum eye & rostrum). There is a constriction separating the 2 lobes. There are no enlarged crystalline cones.

Peduncle of 1st Antenna: As in generic diagnosis in Higher Taxa (S. robustum lappet lacking).

Rostrum: The frontal plate is produced as a slender rostrum reaching to or beyond the anterior margin of the eyes (S. robustum eye & rostrum).

Carapace: The gastric region is domed and bears a small keel anteriorly (S. robustum).

Thoracic legs: The 3rd thoracic leg is elongated and bears a true chela (Stylocheiron-elongated legs) in which the elongate dactyl segment is distally curved and bears a cluster of small grasping teeth. The dactyl segment is opposed by a slender hook of similar length extending from the propodus.

Abdomen: There are no mid-dorsal keels. Length : height of the 6th segment is about 1.7 (S. robustum).

Length: Adults are 13-18 mm.

Petasma: The terminal process bends sharply outward distally, ending acutely. The proximal process is longer than the terminal, and the distal 1/3 is relatively slender, ending sub-acutely. The lateral process is slender, acute and 1/4-1/2 as long as the proximal process (S. robustum petasma).

Thelycum: Described by Costanzo and Guglielmo, 1991.

Comments: The stout appearance of the thorax and the abdominal segments and particularly the short 6th segment are characteristic. S. robustum is a member of the "S. maximum group", along with S. maximum and S. abbreviatum. These 3 species are the only members of the Stylocheiron genus that have elongated 3rd legs that terminate in true chelae in which the dactylus articulates against a branch of the propodus.

HORIZONTAL DISTRIBUTION
S. robustum occurs in the North and South Pacific, the Indian Ocean, and the North and South Atlantic Ocean including the Gulf of Mexico (S. robustum distribution). It is found in the middle parts of the central water mass regions and the western tropical Pacific, --all particularly oligotrophic areas.

VERTICAL DISTRIBUTION
The adults have been caught above 280 m.

LARVAE
Undescribed.

Kingdom Animalia
Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Subclass Eumalacostraca
Superorder Eucarida
Order Euphausiacea
Family Euphausiidae
Genus Stylocheiron
Species Stylocheiron robustum

Status in World Register of Marine Species

Accepted name: Stylocheiron robustum Brinton, 1962

Scientific synonyms and common names

Stylocheiron robustum n. sp. Brinton, 1962

Baker, A. de C., B. P. Boden and E. Brinton, 1990. A practical guide to the euphausiids of the world. British Museum (Natural History), London. 96 pp.

Brinton, E., 1962a. Two new species of Euphausiacea, Euphausia nana and Stylocheiron robustum from the Pacific. International Journal of Crustacean Research, Leiden 4: 167-179.

Brinton, E., 1962b. The distribution of Pacific euphausiids. Bulletin of the Scripps Institution of Oceanography, University of California 8: 51-270.

Brinton, E., 1975. Euphausiids of Southeast Asian Waters. Naga Report. Scientific Results of Marine Investigations of the South China Sea and the Gulf of Thailand 4(5): 1-287.

Costanzo, G. and L. Guglielmo, 1991. Diagnostic value of the thelycum in euphausiids. II. Oceanic species. Genus Stylocheiron. Journal of Crustacean Biology 11: 437-450.

James, P. T., 1983. The distribution of euphausiids along 32°N in the Atlantic Ocean. Institute of Oceanographic Sciences Report 171: 1-47.

Mauchline, J. and L. R. Fisher, 1969. The biology of euphausiids. Advances in Marine Biology 7: 1-454.

Mauchline, J., 1980. The biology of mysids and euphausiids. Advances in Marine Biology 18: 1-681.

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