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(Bosc, 1802)

Description
A shelled, uncoiled, pyramidally shaped, pelagic snail.
Shell transparent, very broad triangular in shape and in cross-section, the elongated dorsal and lateral ribs pronounce this shape. The shell is hyaline, glassy, distinctly curves dorsally. The transverse striation is well developed resulting in a transverse undulation of the shell especially dorsally. The dorsal and lateral ribs are elongated and form long spines protruding from the shell aperture border. [C.cuspidata-ph].
The greatest width of the shell, between the points of the spines, is found in or below the middle. Juveniles without the shell spines and transverse striation are distinguished on this character from the forma Clio pyramidata 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. 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.
Radula formula 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 [C.cuspidata-r].
Juveniles: 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. Juveniles differ from related species by the very strong curvature of the shell. Protoconch I is globular with a very prominent caudal tooth [C.cuspidata-protoc]. An incision separates protoconch I and II, the latter is cylindrical over its whole length.

Colour
The reddish dark brown visceral mass is seen through the shell wall. Growth lines are prominent, the lateral sides are rounded in cross section.

Size
Shell measures up to 20 mm long and up to 30 mm wide.

Ecology
C. cuspidata is a good swimmer that feeds on phytoplankton and protozoa. The temperature range is 15.3°-23.0°C. Sometimes it occurs in mass blooms.

Depth range
Epipelagic.

Remarks
Sometimes hydroids of Campaniclava cleodoae (Gegenbaur, 1854) are found on the shell of C. cuspidata.

Distribution in the North Sea
Northern North Sea, entering from the NE Atlantic.

World distribution
A worldwide warm-water species. In the E Atlantic, east of 40°W, present between 65°N and 20°S, from there entering the northern North Sea; absent from the Channel. Also present in the Mediterranean.

[After Van der Spoel et al., 1997]

Clio cuspidata