A review of bipolarity concepts: History and examples from Radiolaria and Medusozoa (Cnidaria)

Abstract

Bipolarity, its history and general interpretation are investigated and discussed herein. Apart from the classical view, namely that a bipolar distribution is a peculiar biogeographical phenomenon, we propose that it is ecologically controlled too. This approach was used for bipolarity assessment within the following groups: Phaeodaria, Nassellaria, Spumellaria (Radiolaria) and Medusozoa (Cnidaria). We recognize 46 bipolar radiolarian species and three radiolarian genera. However, although species concepts in radiolarians are relatively stable and well known, the high-rank taxonomy of radiolarians is still not well defined. Caution should therefore be taken in the interpretation of distribution data at a taxonomic level higher than the species. In the Medusozoa, bipolarity is observed for 23 species and 32 genera. The different ways in which bipolarity can develop are discussed under the different groups, but preference has been given to the recent and most probable routes of migration. In our investigation of the bipolarity phenomenon, we reviewed more than 400 articles dealing with taxonomy, ecology and biogeography of the modern fauna in both groups.

Glaciambulata neumayeri gen. et sp. nov., a new Antarctic trachymedusa (Cnidaria: Hydrozoa), with a revision of the family Ptychogastriidae

“…23.9.1.1. are not met; the junior synonym, laciniata, has been used only five times in the literature (Bouillon et al 2001(Bouillon et al , 2006Stepanjants et al 2006;Lindsay & Pagès 2010;Mahuzier & Sylvestre 2016), instead of at least 25 times, and Art. 23.9.1.2. is not fulfilled.…”

First bipolar benthic brooder

“…the Pangea break-up or PlioPleistocene glaciations (Crame 1993). There are suggestions that organisms from both hemispheres may have been able to breach the tropics repeatedly during the last 200 million yr (Lindberg 1991, Crame 1993, Stepanjants et al 2006. Since the earliest fossil record of a member of Calloporidae, to which Callopora weslawski belongs, is from the Late Albian (ca.…”

“…Low-latitude sedimentary records indicate the presence of subpolar planktonic foraminifera within the equatorial zone during these cooling cycles (McIntyre et al 1989). Another possibility driving bipolar distributions is isothermal submergence, that is, passage through the tropics via off-shelf or abyssal currents (Stepanjants et al 2006). The Weddell Sea (where C. weslawski specimens were sampled in the Antarctic) is a key source of Antarctic Bottom Water, which provides much of the deep water of the World Ocean.…”

“…The bipolar distribution of biota is defined as the spread over a region in the high Northern and Southern Hemispheres, with a gap between the two (Ekman 1953, Stepanjants et al 2006). Here we consider extreme bipolarity between the 2 polar regions.…”

“…Possible paths of distribution are discussed, including the Pangea break-up, Plio-Pleistocene glaciations, isothermal submergence via offshelf or abyssal currents and anthropogenic transport. records indicating potential bipolar biota distributions and/or exchanges both in the geological past and in recent times (Lindberg 1991, Crame 1993, Stepanjants et al 2006, Pawlowski et al 2007). This was first observed more than 150 yr ago (e.g.…”