Taxonomic revision of Spiniferites elongatus (the resting stage of Gonyaulax elongata) based on morphological and molecular analyses

Abstract

We restudied the morphological complex comprising the cyst-based species Spiniferites elongatus/ Spiniferites frigidus/Rottnestia amphicavata. We reviewed existing studies, and acquired new morphometric measurements of recent cysts from across the Northern Hemisphere, scanning electron microscopy (SEM) observations of cysts from Barents Sea surface sediments, and genetic analyses of cysts from the Beaufort Sea. The measurements suggest that populations and morphospecies cannot be distinguished based on morphometric criteria. Furthermore, sequential sediment trap samples from Hudson Bay reveal that morphological variation can occur at the same location over a few weeks, arguing against a uniform morphological response to environmental parameters. The SEM observations reveal a consistent gonyaulacacean tabulation (Po, 4 0 , 6 00 , 6c, 5 s, Ã 6 000 , 1p, 1 0000). The small and large subunit ribosomal RNA genes and the internal transcribed spacer sequences obtained from differing cysts from the Beaufort Sea with morphologies attributable to the complex, including forms that correspond to Rottnestia amphicavata, were all identical and conform to those of Gonyaulax elongata from the Orkney Islands. The molecular analyses thus support the conclusion that the morphological variability is not reflected genetically and occurs within one species. Based on arguments against the generic attribution of amphicavata to Rottnestia, the continuum between the extreme ends of the morphological range, and the molecular data, we suggest Rottnestia amphicavata to be conspecific with Spiniferites frigidus, and both to be junior synonyms of Spiniferites elongatus. The morphometric data further indicate that Spiniferites ellipsoideus, an elongate cyst from the Miocene, can also be considered a junior synonym of Spiniferites elongatus. It is recommended to use two informal types in census work (i.e. Spiniferites elongatus-Beaufort morphotype for morphologies formerly assignable to Spiniferites frigidus/Rottnestia amphicavata, and Spiniferites elongatus-Norwegian morphotype for cysts with strongly reduced processes) to separate specimens at both extreme ends of the morphological spectrum from typical specimens of Spiniferites elongatus.

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

“…Dimensions. Central body width 23-41 µm, central body length 42-64 µm, process length 5-22 µm (Van Nieuwenhove et al, 2018).…”

“…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.…”

Distribution and (palaeo)ecological affinities of the main Spiniferites taxa in the mid-high latitudes of the Northern Hemisphere

“…Hence, it is tempting to associate the most elongated morphotypes to cold settings. However, systematic observations and measurements of the length and width of the cyst and septa have still not provided a statistically clear relationship between morphometry and environmental parameters (Van Nieuwenhove et al 2018).…”

Using RDNA sequences to define dinoflagellate species

“…Under these circumstances, the distinct species-specific rDNA clusters present in the phylogeny can be used as the primary character upon which a new species is described, along with a detailed morphological description and the known overlap with other species (Figs 5B and 6). When only field collected cells are available for carrying out the morphological characterization, the corresponding rDNA or transcriptomic sequences can generally be obtained using single cell PCR amplification methods [108][109][110][111][112]. Once obtained, as in the case of achieving type genomic DNA in a herbarium, anytime rDNA sequences are used as a primary character for delineating species, representative rDNA sequences should be deposited in GenBank and listed in the species description paper as type DNA sequences.…”