Clione limacina
Clione limacina, known as the naked sea butterfly, sea angel, and common clione, is a sea angel (pelagic sea slug) found from the surface to greater than depth. It lives in the Arctic Ocean and cold regions of the North Atlantic Ocean. It was first described by Friderich Martens in 1676 and became the first gymnosomatous (without a shell) "pteropod" to be described. Distribution. "Clione limacina" is found in cold waters of the Arctic Ocean and North Atlantic Ocean, ranging south at least to the Sargasso Sea. There are three other species in the genus, which formerly were  included in "C. limacina" (either as subspecies, variants or subpopulations). These are "C. elegantissima" of the cold North Pacific (at least north to the Gulf of Alaska; the Beaufort Sea is inhabited by "C. limacina"), "C. okhotensis" of the Okhotsk Sea (where it overlaps with "C. elegantissima"), and "C. antarctica" of Antarctic waters. Description. There are two subspecies that differentiate in body length. The northern subspecies lives in colder water, matures at and can reach a size of . This makes it by far the largest sea angel. In comparison, the size of the southern subspecies is , "C. elegantissima" is up  to , "C. okhotensis" up to , and "C. antarctica" up to . The neurobiology of this pteropod has been studied in detail. Ecology. "Clione limacina" inhabits both the epipelagic and mesopelagic regions of the water column. Feeding habits. Adults feed in a predator-prey relationship almost exclusively on the sea butterflies of the genus "Limacina": on "Limacina helicina" and on "Limacina retroversa". The feeding process of "Clione limacina" is somewhat extraordinary. The buccal ("mouth") apparatus consists of three pairs of buccal cones. These tentacles grab the shell of "Limacina helicina". When the prey is in the right position, with its shell opening  facing the radula of "Clione limacina", it then grasps the prey with its chitinous hooks, everted from hook sacs. Then it extracts the body completely out of its shell and swallows it whole. Adult "Limacina" are absent for much of the year, leaving "C. limacina" without access to their main food source. A study of 138 "C. limacina" during a period without adult "Limacina" found that the stomachs of 24 contained remains of amphipods and 3 contained remains of calanoids. This temporary prey change may allow them to survive in periods of starvation, although the species can survive for one  year without food. Under such exceptional starvation in the laboratory the length of slugs have decreased on average from . The earliest larvae stages of "C. limacina" feed on phytoplankton, but from the later laval stage this changes to "Limacina". The development of these two species is parallel and small "C. limacina" feed on "Limacina" of a similar size, while large "C. limacina" avoid small "Limacina" (including its larvae). Life cycle. In Svalbard, the life cycle of "C. limacina" appears to be at least 2 years. It is a hermaphrodite and observations suggest this is simultaneous. It breeds during the spring  and summer, and the eggs are about . "Clione limacina" is a prey of planktonic feeders, such as the baleen whales, which historically led to sailors naming it "whale-food". Some fishes are also its predators. For example, the Chum Salmon, "Oncorhynchus keta", is a major predator of sea angels. References. This article incorporates CC-BY-SA-3.0 text from the reference