Islandinium minutum subsp. barbatum subsp. nov. (Dinoflagellata), a New Organic‐Walled Dinoflagellate Cyst from the Western Arctic: Morphology, Phylogenetic Position Based on SSU rDNA and LSU rDNA, and Distribution

Abstract

A study of modern sediment from the Western Arctic has revealed the presence of a distinctive brown-colored cyst with a spherical central body bearing unbranched processes that are usually solid with a small basal pericoel. Distinctive barbs project from some processes, and process tips are usually minutely expanded into conjoined barbs. The archeopyle is apical and saphopylic. This cyst corresponds to Islandinium? cezare morphotype 2 of Head et al. (2001, J. Quat. Sci., 16:621). Phylogenetic analyses based on the small and large subunit rRNA genes infer close relationship with Islandinium minutum, the type of which is that of the genus. Re-examination of specimens of I. minutum reveals the presence of minute barbs on its processes, but differences with Islandinium? cezare morphotype 2 remain based on size, process distribution, and barb development. Furthermore, the internal transcribed spacer shows I. minutum to be distinct from this morphotype. On the basis of these small but discrete differences, we propose the new subspecies Islandinium minutum subsp. barbatum subsp. nov. Molecular sequencing of other cysts encountered, namely Echinidinium karaense, an unidentified flattened cyst, and "Polykrikos quadratus", places them in the Monovela clade, the latter showing greater morphological variability than previously thought.

An overview and brief description of common marine organic-walled dinoflagellate cyst taxa occurring in surface sediments of the Northern Hemisphere

“…Morphotype 2, characterized by one or more minute barbs on the process stems and since determined to have a saphopylic apical archeopyle, has now been placed within Islandinium minutum subsp. barbatum (Potvin et al, 2018). The questionable generic assignment of Islandinium?…”

“…minutum (autonym) differs from Islandinium minutum subsp. barbatum in having process surfaces that appear smooth under light microscopy, although minute barbs have been observed under SEM (Potvin et al, 2018) making the distinction between these two subspecies less clear.…”

“…Unknown but molecular phylogeny shows a close relationship with Islandinium minutum subsp. minutum (Potvin et al, 2018). (Reid, 1977).…”

“…The importance of a standardized taxonomy and nomenclature became increasingly apparent during these studies, and was addressed by Rochon et al (1999) who provided comparative descriptions, illustrations and distributional maps of 43 taxa commonly found in modern sediments of the North Atlantic realm. Since then, several taxonomic studies (e.g., Head et al, 2001Head et al, , 2006Pospelova and Head, 2002;Head, 2003;Matsuoka et al, 2009;Li et al, 2015a;Mertens et al, 2015Mertens et al, , 2016Gurdebeke et al, 2018;Limoges et al, 2018;Marret and Mertens, 2018;Potvin et al, 2018;Van Nieuwenhove et al, 2018;Head et al, this issue; Head and Mantilla-Duran, this issue) have advanced our understanding of these cysts. The present work updates Rochon et al (1999) and incorporates new advances in providing descriptions and lowest stratigraphic occurrences of 51 dinoflagellate cyst species and two informal cyst morphotypes that are encountered on a regular basis in Upper Pleistocene through modern marine sediment samples from the Northern Hemisphere.…”

A review of rare, poorly known, and morphologically problematic extant marine organic-walled dinoflagellate cyst taxa of the orders Gymnodiniales and Peridiniales from the Northern Hemisphere

“…Islandinium pacificum resembles Islandinium minutum subsp. barbatumPotvin et al (2018) both in size range and nature of the processes, but is distinguished by the surface texture of the central body wall (smooth vs. faintly to prominently granulate).…”