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Clio cuspidata (Bosc, 1802)

Overview

This is a shelled, uncoiled, pyramidally shaped, pelagic snail, up to 2 cm long. The shell is transparent, very broad triangular in shape and in cross-section, the elongated dorsal and lateral ribs pronounce this shape. The reddish dark brown visceral mass is seen through the shell wall. Growth lines are prominent, the lateral sides are rounded in cross section. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the warmer waters of all oceans in the upper water layers where it can sometimes occur in mass blooms (Clio cuspidata 1).

Taxonomic Description

The shell hyaline, glassy, distinctly curves dorsally. The transverse striation is well developed resulting in a transverse undulation of the shell especially dorsally (Clio cuspidata dorsal). The dorsal and lateral ribs are elongated and form long spines protruding from the shell aperture border (Clio cuspidata line drawing). The greatest width of the shell, between the points of the spines, is found in or below the middle, this is a typical difference as compared to Clio p. forma lanceolata. Juveniles without the shell spines and transverse striation are distinguished on this character from the forma lanceolata. By the posterior position of the lateral spines the aperture is very large and reaches far caudally. The ventral surface is regularly rounded and the ventral rib appears as a small swelling in the middle, the rib disappears near the shell aperture as it becomes broader anteriorly. The two latero-dorsal sides separated by the dorsal rib have two slightly marked ribs each. The dorsal side of the shell protrudes above the ventral side (Clio cuspidata 1). The lateral and dorsal ribs are gutter-shaped, when seen from the inside. Though rather straight at their ends the lateral ribs clearly bend and diverge in their caudal part. The embryonic shell in adults is nearly perfectly round, but in young specimens the sharp cusp at the tip of the embryonic shell is not yet worn off. The Clio cuspidata radula formula is 1-l-l, it is composed of some 10 transverse rows but in the frontal rows the median plates are lost while and the lateral rows diverge strongly.
Shell measurements are: up to 20 mm long and up to 30 mm wide.

Morphology and Structure

A unique structure in this species is the intestine appendage. This organ is found at the most caudal coil of the intestine, where the rounded appendix projects beyond the liver. It has a fringe of longitudinal and radiating muscles at its base and the lumen goes directly into the lumen of the intestine where a deep groove runs along its wall. The presence of this appendage indicates that this species is not closely related to Clio pyramidata though a resemblance with Clio pyramidata forma lanceolata is present.
The morphological changes of the mantle during growth include the shifting of the lateral mantle appendages from posterior to anterior and the disappearance of one of the mantle zones with polygonal cells in older specimens. These changes seem, however, not dependent on changes of the cell activity.

Juveniles

Juveniles differs from related species by the very strong curvature of the shell. The Clio cuspidata protoconch I is globular with a very prominent caudal tooth. An incision separates protoconch I and II, the latter is cylindrical over its whole length.

Reproduction

The species is a protandric hermaphrodite.

Ecology

The species is phytophagous and epipelagic. The temperature range is 15.3°-23.0°C.

Distribution

The species demonstrates the difference between E and W-Atlantic Ocean water masses; in the W-Atlantic only a small population is present between 15°N-40°N off the N-American coast. East of 40°W Clio cuspidata is found between 65°N-20°S. The influence of the Gulf Stream is evident as the species is clearly linked to this stream in its area north of 50°N. In the southern part of the E-Atlantic the influence of the Benguela Current is evident as it carries the species far north. In the Central and East Indian Ocean Clio cuspidata has only been found at three localities. Clio cuspidata is a warm-water species, see the Clio cuspidata map.

Geological Record

This species was known from the Late Quaternary of the Red Sea; the Pleistocene of the Mediterranean (it has a continuous record from Alleröd to present). After the Younger Dryas it lives in the Adriatic. It is found in the Mid Pliocene of Italy.

Others

Sometimes hydroids of Campaniclava cleodoae (Gegenbaur, 1854) are found on the shell of this species.

Types

Hyalaea cuspidata Bosc, 1802: 241, pl. 9, figs. 5-7.
Not found in MHNP a type has been indicated. In MHNP there are many specimens to which Bosc (1802) may have referred, but none were found type material.

Clio cuspidata