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Styliola subula (Quoy and Gaimard, 1827a)

Overview

This is a shelled pelagic snail, up to 1.3 cm long, with a completely transparent uncoiled, needle-like shell. The cross-section is round. In the upper part of the shell a rib is found that projects from the aperture rim-like a cusp. The surface has growth lines. The shell is long, tubular and not curved. The visceral mass is seen through the shell. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the warm upper waters of all oceans, where it can occur in mass blooms (Styliola subula line drawing).

Taxonomic Description

Small conical shell, round in cross-section (Styliola subula, Styliola subula shell). The width of the aperture in adults is smaller than the shell diameter, just posterior to the aperture. A triangular tooth may be found dorsally and a triangular incision ventrally at the aperture border (Styliola subula shell details). The groove (Styliola subula struct. inside groove, Styliola subula groove outer structure) at the dorsal side of the shell is variable and more or less twisted so the caudal point of the groove is at the left of the median line and the cranial point in the median (Styliola subula aperture&groove). The posterior shell parts, with the embryonic shell, are pointed and show two constrictions above each other. The shell has faint transverse striation; in between these striae are very minute longitudinal striation. The rose-coloured wings are undulated at the border, the visceral mass is rose or red. The balancer is clearly seen at the left mantle border. The Styliola subula radula formula is 1-1-1.
The length of the shell is up to 13 mm. The rear angle of the shell is 11°.

Juveniles

The shell development is regular so that the juvenile represents the pointed oval protoconch I with cylindrical protoconch II gradually but slowly increasing in width and finally showing two incisions (Styliola subula protoconch). The soft parts develop slower than the shell so that after the veliger stage a skinny stage occurs. In this stage the too small soft parts are long drawn in a adult shell.

Reproduction

The species is a protandric hermaphrodite.

Ecology

The species is phytophagous and epipelagic. The temperature range and salinity range are about 13.8°-27.8°C and 36.8°/oo and 36.5°/oo, respectively (Menzler, 1958; Wormelle, 1962).

Distribution

This species shows a distribution similar to Creseis. It lives in all oceans between 40°N-40°S. The northern boundary of the species in the Atlantic indicates a small, but distinct, influence of the Gulf Stream and the Labrador Current, the first current sometimes transports specimens as far north as 60°N. The cold W Australian Coast Current is the cause of its absence west of Australia, see the Styliola subula map.
One exceptional record south of the West Wind Drift at 64°S is due to current influences. The species is known to have a pantropical distribution, though the species is less abundant between 10°N and 10°S. It is most abundant in the Atlantic, 10° south of its northern limit and 10°N, and between 10° north of its southern limit and 10°S. This species is not typically oceanic and this is demonstrated by its occurrence in the Mediterranean, the Caribbean Sea, the China Sea and the Red Sea. In the Indian Ocean the species is most abundant in the southern part of its area though it may penetrate deeply into the Red Sea and the Arabian Sea. The species shows a clear diurnal vertical migration in the Mediterranean, the mean day level is between 800 and 200 m while the night concentration is near the surface. In the Florida Current a mean night level at 81 m and a mean day level at 234 m occurred, while the juveniles were found 50-200 m below the adults at night. The juveniles migrate up and down over 300 m while the adults migrate over 400 m. The maximum depth at which the species was recorded is 1500 m, but it is found most frequently between 50-100 m.

Geological Record

This species is known from the Late Quaternary (during the last interglacial 100.000 BP) of the Red Sea, and the Pleistocene of the Mediterranean. In the Adriatic Sea it is found only since the Sub-Atlanticum. This species is known from the Miocene of Australia.

Others

Neurosecretion is described for this species.

Types

Cleodora subula Quoy and Gaimard, 1827: 233, pl. 8d, figs. 1-3.
Types not found in MHNP.

Styliola subula