Bipolar distribution of Clione and Limacina

Dear Yasuhiko,
It must have been an interesting adventure - if rather cold - diving in Antarctica. If you have any photos you would like to share they would be very welcome.

Concerning your question about pteropod distribution. One major problem with any interpretation of pteropod distributions is not being sure how to define a species? For example, if you have animals with long spines and others with short spines, are they an example of clinal variation within one species caused by physical parameters such as water temperature or salinity, or are they a genetic differences suggesting different species? We still have much to learn. Certainly the more traditional view of Clione is that there is one bipolar species. Van der Spoel (1967) has a long discussion on the various hypotheses explaining how bipolar distributions may have evolved through the affects of climate change, tectonic plate movement, leading to relict populations etc. Some of these factors most probably were involved in developing the two disjunct populations at either end of the world, but just because the populations may have arisen from the same parent population, that is no reason to consider them to still be a single species. After all, isolating factors are one of the mechanisms which bring about speciation. Gilmer & Lalli (1990) studied the anatomy of animals from both populations and from their anatomical studies, concluded that there were sufficient differences to justify considering the southern hemisphere population to be a distinct species, Clione antarctica (Smith, 1902).

• Gilmer, R.W. & Lalli, C.M. (1990) Bipolar variation in Clione, a gymnosomatous pteropod. Am. Malacol. Union Bull. 8(1): 67-75.
• van der Spoel, S. (1967) i>Euthecosomata. a group with remarkable developmental stages (Gastropoda, Pteropoda). J.Noorduijn en Zoon N.V.: Gorinchem, Netherlands.

Best wishes,
Bill Rudman