The genus Ammonia Bruennich, 1772; its geographic distribution and morphologic variability

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Abstract
Three morphotypes of Ammonia are recognized, assigned to the species A. beccarii, but differentiated as forma tepida, forma parkinsoniana, and forma beccarii. Forma tepida and forma parkinsoniana are ecophenotypes and constitute the end members of a gradational series. Forma beccarii may also be an ecophenotype but available data are not conclusive. The geographic distribution of Ammonia extends from the Faeroe Islands, Denmark in the northeast Atlantic (62.degree.N) to South Africa, throughout the Mediterranean and the Indian Ocean, around Australia and New Zealand as far as 45.degree.50''S. In the western Atlantic, Ammonia extends from Miramichi Bay, Nova Scotia [Canada] (47.degree.10''N) in the north to Isla de los Estados, Tierra del Fuego, Argentina, in the south (about 55.degree.S). The northermost Pacific occurrences are Samish Bay, Washington [USA] (about 48.degree.N) on the east and Hokkaido, Japan (about 45.degree.N) on the west. These distributions are controlled by the latitudes (and protected waters) where the temperature reaches 17-22.degree. C at least one month during the year. This temperature range is the minimum reproductive temperature of Ammonia determined experimentally. Occurrence data from samples and the literature substantiate the fact that the primary environmental control over the geographic distribution of Ammonia is the presence of the minimum reproductive temperature (17-22.degree. C). The extreme northern and southern occurrences of Ammonia possibly indicate some acclimation of the minimum reproductive temperature but also could represent relict or allopatric populations. Varying morphologies are discussed and contrasted within the wide geographic range of Ammonia.