Clio recurva (Childern, 1823)
This is a large shelled pelagic snail, up to 3 cm long, with a transparent uncoiled shell. The shell is triangular in shape. The cross section is oval and the lateral sides are gutter-shaped. The reddish dark brown visceral mass is seen vaguely through as the shell is relatively thick. It is a good swimmer that feeds on phytoplankton and protozoa. It lives in the deeper water layers of all oceans (Clio recurva line drawing).
The shell is straight except for the posterior most part which is faintly curved dorsally. The width of the aperture is 1/2 or more of the total shell length. The sculpture consists of concentric undulations which produce a wavy transverse striation. Three conspicuous dorsal ribs are present, the middle one is the broadest. The ventral rib is so large that it nearly covers the whole ventral side. (Clio recurva line, Clio recurva). The lateral ribs of the ventral side are double, a flat lateral surface is found between each two ribs, which anteriorly may be concave, gutter-shaped (Clio recurva lateral side). Specimens found off the coast of California are slightly different from the Atlantic ones, they most resemble those of the West Indies. These differences seem to depend on individual variations. The Clio recurva radula formula is (1)-1-1-1-(1) and sometimes 1-1-1 (Clio recurva radula 2). The embryonic shell is oval rounded with a clear cusp which in older specimens may be worn off, and thus it resembles very much that of Clio cuspidata. The differences in character of the shells in young specimens of 5-8 mm and the full-grown ones are not essential as these juvenile characters persist in full-grown specimens. The musculature of the wings and mantle and columellar system are strongly developed (Clio recurva muscles stained, Clio recurva wing muscles).
Shell measurements are: up to 30 mm long, 17 mm wide. It is the largest species in the genus.
A special description is not available.
The species is a protandric hermaphrodite. It is ovoviviparous, thus having brood protection.
The species is phytophagous. It is considered as meso- or hypo-planktonic, but in reality it is an epi-planktonic species that also can be found at deep depths. The tropical distribution type of the species is slightly pronounced; may be is not strictly tropical.
It occurs between 40°N and 60°S in all oceans. Like Clio chaptali the distribution of this species is, as far as known, discontinuous. The species sometimes bathypelagic but it is mostly hypopelagic and not strictly tropical. Records from near Cape Horn concern are rare, but the population near the subtropical convergence proves that the species penetrates transitional areas. see the Clio recurva map.
Sometimes the hydroids of Campaniclava clionis Vanhöffen, 1910 are found on the shell of this species (Clio recurva w/ hydroids, Clio recurva w/ hydroids detail, Camp.clionis op C.recurva, Clio recurva+ Camp.clionis).
Balantium recurva Childern, 1823: 220, pl. 7, fig. 107.
The types could not be located.