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Stylocheiron carinatum G.O. Sars, 1883

Etymology: Stylocheiron - a column/hand; carinatum - with a keel

Eye: The eye is bilobed with the lower lobe large and nearly spherical (S. carinatum eye & rostrum). The upper lobe is short and narrow with 6-8 enlarged crystalline cones in a distal transverse row (Stylocheiron table).

Peduncle of 1st antenna: As in the generic description in Higher Taxa (S. carinatum lappet lacking).

Rostrum: In the female it is straight and acute, extending beyond the anterior limit of the eye. In the male it is narrower, and not reaching the anterior limit of the eye (S. carinatum eye & rostrum) (S. carinatum dorsal head).

Carapace: The gastric region is a low dome or only slightly elevated, but with a distinct dorsal keel, originally described as a carina (S. carinatum).

Thoracic legs: The elongated 3rd thoracic leg has the propodus (penultimate segment) bearing only 1-3 short setae on the upper, anterior edge and three longer setae on the lower or posterior edge. These longer setae are directed latero-distally so as to form, together with similar curving setae on the dactylus, a false chela or grasping organ.
This grasping organ is like the "false chela" found in the other species of the "S. carinatum group" (Stylocheiron-elongated legs). The combined length of a distal tubercle and spine on the carpus (antepenultimate segment) on the elongated 3rd leg is less than 1/4 of the length of the propodus in subtropical waters but often appears to be nearly 1/3 in tropical waters. The propodus bears only one or two short curved setae along its length, in addition to 3 longer bristles (S. carinatum thoracic leg).

Abdomen: The body is slender. The 6th abdominal segment is long, approximately 2.2 times as long as high (S. carinatum).

Length: Adults are 6-12 mm.

Petasma: The terminal process is flat and broad with a truncated, crenulated or finely serrated end and sometimes with two short spine-like projections on the inner edge according to Brinton (1975). The proximal process is even broader, and longer than the terminal process with minute crenulations on the distal margin. The lateral process is a little shorter and much more slender than the proximal process. It terminates in a curved tooth and bears a smaller outer tooth just before its end (S. carinatum petasma).

Thelycum: Described by Costanzo and Guglielmo, 1991.

Comments: S. carinatum is closely related to S. armatum, but it is distinguishable by the combined length of the distal tubercle and its spine on the carpal segment of the elongated 3rd leg being less than 1/2 the length of the propodal segment, often much less. Also the propodal segment of the 3rd leg lacks the numerous bristles that help to distinguish S. armatum (S. carinatum dactyl)

S. carinatum is consumed by fishes.

S. carinatum occurs in the Atlantic, Pacific and Indian ocean basins, 40°N to about 35°S, but not in the cooler parts of the eastern boundary currents (S. carinatum distribution). This "warm-water cosmopolitan" range of S. carinatum requires re-examination in view of variability in characters separating S. armatum and S. carinatum.

Most of the population is above 140 m day and night, hence its presence in the Eastern Tropical Pacific where deeper waters are 02-deficient.

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

Metanauplius - (S. carinatum A)

Shape - The carapace is smooth and rounded.
Marginal spines - absent

Calyptopis - (3 stages) (S. carinatum B)

Shape - There are large lateral lobes in C1-C2.
Marginal spines - absent
Postero-dorsal spine - absent
Lateral denticles - absent
Dorsal keel - A small keel is present in C3 situated on the posterior half of the carapace.

Postero-lateral spines - PL3 is longer than PL2.
Terminal spines - There are 6 terminal spines in C1-C2.

Furcilia - (5 stages) (S. carinatum C)

Eye: The eye has a bilobed appearance in F2.

Frontal plate / rostrum - The rostrum is acute.
Marginal spines - absent
Postero-dorsal spines - absent
Lateral denticles - absent
Dorsal keel - A distinct dorsal keel is situated in the posterior half of the carapace in F1 and nearer the midpoint in F2-F3.

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

Mid-dorsal spines - absent

Pleopods: The common developmental pathway is 0 - 1' - 1"2' - 3"2'- 5".

Postero-lateral spines - PL3 is longer than or nearly equal to PL2. PL1 becomes ventrally situated in F2.
Lateral spines - One pair of lateral spines is present with relatively proximal position.

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

Lebour (1949) observed metanauplii hatching from the eggs of Stylocheiron carinatum taken near Bermuda. She noted that the first and second antennae were partially covered by unshed cuticle. The mandible, reduced to a single stump, was covered by a loose jointed cuticle. Lebour also described a nauplius with 3 pairs of biramous, setose limbs which had hatched from another sample of S . carinatum in the Atlantic. She suggests that this form hatched prematurely.

Ponomareva (1969) observed larvae hatching from eggs in the Indian Ocean population of Stylocheiron carinatum . The newly-hatched larva has a heart-shaped configuration and differs from the larvae described by Lebour.

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

S. carinatum, selected stages
S. carinatum A [egg, metanauplius]
S. carinatum B [calyptopis 1-3]
S. carinatum C [furcilia 1-3]
key to larval illustrations

Stylocheiron carinatum