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Stylocheiron elongatum G.O. Sars, 1883

Etymology: Stylocheiron - a column/hand; elongatum - elongate

Eye: The eye is cylindrical in appearance, with the upper and lower lobes equal in width (S. elongatum eye & rostrum). The overall height of eye is 1.4-1.7 mm. The upper lobe has 13-16 only slightly enlarged crystalline cones in a distal transverse row (Stylocheiron table).

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

Rostrum: It is extremely short in both sexes. The frontal plate is produced as an acute triangle which narrows to a short spiniform process at the apex (S. elongatum dorsal head) (S. elongatum eye & rostrum).

Carapace: The gastric area is elevated as a low dome with a low median keel (S. elongatum).

Thoracic legs: The 3rd leg is greatly elongated, with a false chela formed of distal bristles on the propodus and dactylus. This grasping organ is like the "false chela" found in other species of the "S. longicorne group" (Stylocheiron-elongated legs).

Abdomen: The 6th segment is extremely elongated, with length : height being about 4.2 (S. elongatum) (S. elongatum photo).

Length: Adults are 11.5-18 mm.

Petasma: The terminal and proximal processes are slender, of similar length, and tapering to acute tips. The tip of the proximal process curves inward. The lateral process is minute (S. elongatum petasma).

Thelycum: Described by Costanzo and Guglielmo, 1991.

Comments: This species is characterized by the long slender body with an elongated 6th abdominal segment that is equal to or slightly longer than the combined lengths of the 4th and 5th segments.

ECOLOGY
S. elongatum is consumed by fishes.

HORIZONTAL DISTRIBUTION
S. elongatum is present in the Atlantic Ocean between 40°N and 40°S but has been found northward to Iceland, 65°N, in the Gulf Stream extension. In the Pacific Ocean it occurs between 40°N and 35°S but not in the 02-deficient parts of the Eastern Tropical Pacific. In the Indian Ocean it is between about 10°N and 40°S, being absent in the 02-deficient Bay of Bengal and Arabian Sea (S. elongatum distribution).

VERTICAL DISTRIBUTION
S. elongatum lives at 200-500 m depth, deeper than any other member of the "Stylocheiron longicorne group".

LARVAE
See the development summary (S. elongatum Table) for the stage descriptors and length in stage.

Metanauplius - undescribed

Calyptopis - (3 stages) (S. elongatum A)

Carapace:
Shape - The carapace is short in relation to the abdomen length by C3. There is a large lateral lobe in C1.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent

Telson:
Postero-lateral spines - PL3 is very long.
Terminal spines - There are 6 terminal spines in both C1 and C2.

Furcilia 1-2 (S. elongatum B)

Eye: The pigmented area is cylindrical.

Carapace:
Shape - The carapace is short in relation to the abdomen length.
Frontal plate / rostrum - The rostrum is narrow and acute.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - absent

Thoracic legs: There is precocious development of leg 3, the elongate leg of the adult, in the furcilia phase.

Abdomen:
Mid-dorsal spines - absent
Segment 6 - Segment 6 becomes elongate.

Telson:
Postero-lateral spines - PL3 is relatively long.

Comments: Lebour (1926b) notes that larvae of the genus Stylocheiron are distinguished by no lateral denticles on the carapace in any stage, a relatively long first antennal peduncle with a short flagella, distinctive large eyes, and a common furcilia stage with 1"2' pleopods.

The cylindrical eye and elongate 6th abdominal segment are characteristic of S. elongatum .

Development
(S. elongatum Table), development summary for the stage descriptors and length in stage.

Pictures
S. elongatum, selected stages
S. elongatum A [calyptopis 1-3]
S. elongatum B [furcilia 1-2]
key to larval illustrations

Stylocheiron elongatum