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A high degree of morphological variability is expressed between the ornately sculptured siliceous scales formed by species in the chrysophycean genus,Synura. In this study, we aimed to uncover the general principles and trends underlying the evolution of scale morphology in this genus. We assessed the relationships among thirty extantSynuraspecies using a robust molecular analysis that included six genes, coupled with morphological characterization of the species‐specific scales. The analysis was further enriched with addition of morphological information from fossil specimens and by including the unique modern species,Synura punctulosa. We inferred the phylogenetic position of the morphologically uniqueS. punctulosa, to be an ancientSynuralineage related toS. splendidain the sectionCurtispinae. Some morphological traits, including development of a keel or a labyrinth ribbing pattern on the scale, appeared once in evolution, whereas other structures, such as a hexagonal meshwork pattern, originated independently several times over geologic time. We further uncovered numerous construction principles governing scale morphology and evolution, as follows: (i) scale roundness and pore diameter decreased during evolution; (ii) elongated scales became strengthened by a higher number of struts or ribs; (iii) as a consequence of scale biogenesis, scales with spines possessed smaller basal holes than scales with a keel and; and (iv) the keel area was proportional to scale area, indicating its potential value in strengthening the scale against breakage.

Diatom metacommunities are structured by environmental, historical, and spatial factors that are often attributed to organism dispersal. In the McMurdo Sound region (MSR) of Antarctica, wind connects aquatic habitats through delivery of inorganic and organic matter. We evaluated the dispersal of diatoms in aeolian material and its relation to the regional diatom metacommunity using light microscopy and 18S rRNA high‐throughput sequencing. The concentration of diatoms ranged from 0 to 8.76 * 10⁶ valves · g⁻¹dry aeolian material. Up to 15% of whole cells contained visible protoplasm, indicating that up to 3.43 * 10⁴potentially viable individuals could be dispersed in a year to a single 2 ‐cm²site. Diatom DNA and RNA was detected at each site, reinforcing the likelihood that we observed dispersal of viable diatoms. Of the 50 known morphospecies in the MSR, 72% were identified from aeolian material using microscopy. Aeolian community composition varied primarily by site. Meanwhile, each aeolian community was comprised of morphospecies found in aquatic communities from the same lake basin. These results suggest that aeolian diatom dispersal in the MSR is spatially structured, is predominantly local, and connects local aquatic habitats via a shared species pool. Nonetheless, aeolian community structure was distinct from that of aquatic communities, indicating that intrahabitat dispersal and environmental filtering also underlie diatom metacommunity dynamics. The present study confirms that a large number of diatoms are passively dispersed by wind across a landscape characterized by aeolian processes, integrating the regional flora and contributing to metacommunity structure and landscape connectivity.

The planktonic dinoflagellatePtychodiscus noctilucacombined distinctive morphological features such as a disk‐shaped anteroposteriorly compressed cell body and an apical carina, together with a flexible and tough cell covering, suggesting intermediate characteristics between thecate and naked dinoflagellates.Ptychodiscus noctilucawas examined by light, epifluorescence, and scanning electron microscopy from specimens collected in the Mediterranean Sea and the North and South Atlantic Ocean.Ptychodiscus noctilucashowed a straight apical groove that bisected the carina, a cell covering with a polygonal surface reticulum, nucleus without capsule, sulcal intrusion in the episome, sulcal ventral flange, and yellowish‐green chloroplasts that are shared characters withBrachidinium/Karenia. The cell division was the typical binary fission of gymnodinioid dinoflagellates, although exceptionally in an oblique transversal axis. We examined the intraspecific variability during incubation experiments. In the fattened cells, termed asPtychodiscus carinatus, chloroplasts transformed into dark granules, and the cell acquired the swollen and smaller stage, termed asP. inflatus.Ptychodiscus carinatus,P. inflatus,andDiplocystis antarcticaare synonyms ofP. noctiluca. Molecular phylogeny based on theSSU rDNAsequence revealed thatPtychodiscusbranched within the short‐branching dinokaryotic dinoflagellates as an independent lineage with affinity toBrachidinium/KareniaandKarlodinium/Takayamain a generally poorly resolved clade. Our results indicated that the order Ptychodiscales, established for unarmored dinoflagellates with a strongly developed pellicle, has artificially grouped thecate dinoflagellates (Kolkwitziella,Herdmania), naked dinoflagellates with thick cell covering (Balechina,Cucumeridinium) and other insufficiently known unarmored genera with typical cell coverings (Brachidinium,Ceratoperidinium).