Comparative analysis of six common foraminiferal species of the genera Cassidulina, Paracassidulina and Islandiella from the Arctic-North Atlantic domain.

Abstract. Morphologically similar benthic foraminiferal taxa can be difficult to separate. Aside from causing
issues in taxonomy, incorrect identifications complicate our understanding of species-specific ecological preferences
and result in flawed palaeoenvironmental reconstructions and geochemical results. Over the years, a
number of studies have grouped together several key Arctic–North Atlantic species in various combinations,
despite their distinct environmental preferences and/or stratigraphical differences, causing great confusion in
the literature. These species include Cassidulina laevigata, Cassidulina neoteretis, Cassidulina teretis, Paracassidulina
neocarinata, Islandiella helenae, and Islandiella norcrossi. Here, we provide for the first time a detailed
comparison of these taxa. We present a compilation of the original species descriptions, along with clear, illustrated
guidelines on how to separate these taxa to circumvent taxonomic confusion. We acknowledge that some
features cannot easily be seen with a standard low-powered microscope, especially if specimens are not well
preserved. In those cases, we recommend the following actions: (i) always strive to make a precise identification
and at least differentiate between the three genera; (ii) where C. neoteretis and C. teretis cannot be separated, and
where the stratigraphical context does not make the species identification obvious, specimens belonging to these
taxa should be reported as C. teretis/C. neoteretis; and (iii) where specimens in a sample cannot be confidently
assigned to a specific species of Islandiella or Cassidulina, specimens should be grouped as Islandiella spp.
or Cassidulina spp., followed by naming the most dominant species in brackets. The improved identification
of Cassidulina, Paracassidulina, and Islandiella specimens will ensure development of a better understanding
of the ecological affinities of these key Arctic–North Atlantic taxa, consequently resulting in more accurate
palaeoenvironmental reconstructions and geochemical data.