The "pteropod" Clione limacina belongs to a group of marine gastropod mollusks that lack shells. This species has been the subject of extensive investigations into the neurobiology of swimming behavior. Its geographic distribution was long considered to be circumpolar (i.e., around both the northern and southern ends of the Earth), with northern and southern hemisphere subspecies. However, work by Gilmer and Lalli (1990) suggested that southern populations should possibly be treated as a distinct species, C. antarctica. Clione limacina is widely distributed in the North Atlantic and Subarctic Oceans and is found also in the North Pacific Ocean and along the Atlantic coast of North America in the waters of the cold Labrador current south to the Cape Hatteras region (around 35 N).
Clione limacina breeds and spawns in all types of water masses within the vertical range it commonly inhabits, i.e., from the surface to around 500 m. The most intensive spawning is correlated with the spring/summer period of annual heating of local water and the highest abundance parallels maximum growth of phytoplankton, which serves as food for veliger larvae and early polytrochous larvae. After the end of this period, spawning intensity in local C. limacina populations declines sharply, although spawning continues at low intensity during the autumn/winter season.
Clione limacina feeds exclusively on shelled "pteropods", such as Limacina helicina (Lalli and Gilmer, 1989). Only the veliger stage ofC. limacina does not feed on Limacina, instead consuming phytoplankton during this life stage. However, 48 to 72 h after metamorphosis from the veliger stage to polytrochous larvae (at around 0.3 mm length) C. limacina begin feeding on Limacina veligers. At sizes greater than 0.6 mm, C. limacina begin to consume metamorphosed Limacina prey and they do so exclusively once they exceed 1.75 to 2 mm in length. Clione capture their Limacina prey with their six buccal cones and the proboscis is used to draw the body out of the shell. The feeding specialization of Clione is reflected in numerous adaptations. Because even the early polytrochous larvae of Clione feed on Limacina, the life cycles of predator and prey are necessarily closely synchronized. The feeding behavior of C. limacina is described in detail by Lalli and Gilmer (1989) and Hermans and Satterlie (1992).
See additional images and information at the Sea Slug Forum for both the arctic and antarctic forms
(Mileikovsky 1970; Lalli and Gilmer1989; Gilmer and Lalli 1990; Hermans and Satterlie 1992)