Morphological study of Chaetoceros wighamii Brightwell (Chaetocerotaceae, Bacillariophyta) from Lake Vrana, Croatia

Abstract

-Chaetoceros wighamiiBrightwell is a planktonic diatom species originally described from brackish waters. Since its original description, the species has been reported in a wide variety of habitats, ranging from freshwater to marine. Varying descriptions exist in the taxonomic literature and several taxa have been considered as synonyms, including freshwater species Chaetoceros amanita. In this study we provide morphological and ultrastructural information on a cultured strain isolated from freshwater sample collected in the Lake Vrana (Vransko jezero) in Croatia, in April 2011. The cells form short and robust chains with very narrow apertures, often partially occluded by silica membranes. Other distinctive features observable in light microscopy are the shape and orientation of the setae which are very long, straight and robust, diverging in various directions from the chain axis and the single parietal chloroplast extending from valve to valve. Distinct ultrastructural characteristics are the absence of processes either in intercalary or terminal valves and the ornamentation of the valve face with densely distributed ribs spreading from an irregular eccentric hyaline area without a clearly defi ned annulus. The outer surface of the terminal valve is ornamented with small spines and setae are composed of fl at longitudinal fi laments interconnected with short bars and ornamented with small spines tightly arranged around the setae. Our description agrees well with that reported for the freshwater morphotypes of C. wighamii (syn. C. amanita) and contributes for a reliable distinction of this intriguing taxon from similar morphotypes. This fi nding supports the interpretation of Chaetoceros wighamii as a freshwater/brackish species and represents the fi rst report of a Chaetoceros species in lacustrine environment in Croatia and possibly in any Central European habitats.

Morphological and genetic diversity of Beaufort Sea diatoms with high contributions from theChaetoceros neogracilisspecies complex

“…We also suggest that cell chains of C. neogracilis , which were described for the first time in this study, might have been wrongly identified as the freshwater species Chaetoceros wighamii Brightwell (http://malina.obs-vlfr.fr; see Bosak et al. for a discussion on C. wighamii ). Similarly, the doubtful reports of C. wighamii from the Baltic Sea and Danish waters could indeed refer to C. neogracilis , as suggested by the morphological and ultrastructural similarity between Arctic strains of C. neogracilis described in this study and culture material from Danish waters attributed to C. wighamii (see fig.…”

Taxonomic relationship between two small-sized Chaetoceros species (Bacillariophyta): C. tenuissimus and C. salsugineus, and comparison with C. olympicus sp. nov. from Catalan coastal waters (NW Mediterranean)

“…In addition, setae in C. wighamii are much stronger and longer and their ultrastructure very different. In C. wighamii, the setae show several rows of small poroids arranged in spiral (Bosak et al, 2015) while in C. olympicus they present a few slightly twisted rows of small rectangular poroids (Figs 30,31). Unfortunately, we have not been able to observe the ultrastructure of the valve for C. olympicus to compare it with that of C. wighamii.…”

“…The morphological features of C. olympicus and C. wighamii are summarized in Table 4. Due to its morphological similarity, the marine species C. bottnicus Cleve (and the associated species C. biconcavum Gran and C. caspicum Ostenfeld) was considered by some authors as a synonym of C. wighamii but was later reconsidered as a separate species by Sánchez Castillo et al (1992) (see Bosak et al, 2015 for further details). The resting spore of C. olympicus is different from that of C. bottnicus, whose resting spore is biconvex with spines in one or the two valves (Sánchez Castillo et al, 1992).…”

“…Morphological characters of C. olympicus compared with two similar chain-forming species: C. tenuissimus (this study) and C. wighamii(Bosak et al, 2015).…”