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The diversity of centric diatoms is documented for the transitional zone of the lower part of the Southern Bug River (Ukraine) just before entering the Dnipro-Bug Estuary and compared to earlier results from the upstream sampling sites of the same river system. Benthic samples of the following sites were investigated: north of Mykolaiv City (approximately 5 km), in Mykolaiv City (near Varvarivskyi Bridge), and 5 km south of the city. Twenty-four centric diatom taxa belonging to 11 genera were identified, analysed, and documented by scanning electron microscopy (SEM) and light microscopy (LM). Among them, Aulacoseira nivalis is the first report for Ukraine, A. islandica and is the first confirmed record for the studied area since the 1930s. The maximum number of centric diatom taxa found in one station was 21, the minimum 10. Melosira subglobosa was the most common (documented in 57–80% of sites with centric diatoms) and abundant species 7.3–15.7% in relative abundance to all diatom taxa. The discovered diversity of taxa and its comparison with previous results is discussed with regard to the relevance of estuary zones in the research of diatoms.

The genus Alveolophora was previously reported only from fossil localities in Asia and the Russian Far East. Three new species of this extinct diatom genus were described from Miocene sediments in western North America, A. bradburyi, A. nevadica and A. americana. The taxa were described using light and scanning electron microscopic observations of valve morphology. These new species from North America were compared with species previously described from Asia. Polymorphism in longitudinal or transverse ribs was detailed. The ribs sometimes formed anastomosing networks, a feature unknown in all previously described members of the genus. Comparison of frustular morphology with other members of the genus as well as the Family Aulacoseiraceae was made. Fossil taxa can provide unique insights into character evolution and phylogenetic relationships.

Examination of samples from different aquatic environments from Brazil revealed the presence of a new Aulacoseira species. Aulacoseira veraluciae Tremarin, Torgan & T. Ludwig is described and illustrated with light and scanning electron microscopy, and its morphology compared with that of similar species, such as A. muzzanensis (Meister) Krammer, A. granulata (Ehrenberg) Simonsen and A. agassizii (Ostenfeld) Simonsen. The new species is characterized mainly by the straight pervalvar rows of areolae, morphology of the linking spines, shape and position of the rimoportulae on the valve mantle, deepness and thickness of the ringleiste.

Aulacoseira veraluciae Tremarin, Torgan & T. Ludwig, sp. nov. (Figs 2‒35) Holotype:— UPCB 76037, Diatom Collection of the Herbarium of Universidade Federal do Paraná, Brazil, illustrated here in Fig. 21. Isotype:— BM 101711 (The Natural History Museum, England). Type locality:— BRAZIL. State of Rio Grande do Sul, Tapes and Mostardas municipalities, Patos lake, 30º23’S / 50º41’W to 32º07’S / 52º12’W, phytoplankton, collected from 07 January 1988 by L.C. Torgan. Etymology:—The new species is named in honor of Dr. Vera Lúcia de Moraes Huszar of National Museum, Rio de Janeiro Federal University, for her dedication to phytoplankton research. Description: — Cells solitary or joined by short spines to form short or long chains, straight or slightly curved. Valve diameter 3–15 µm, mantle height 4–12 µm. Mantle height/diameter ratio 0.35–2.01. Separation valves with face flat, totally or partially covered by areolae and mantle with deep longitudinal depressions formed by the spine insertion of the adjacent cell. Separation spines attenuate and long (ca. 3‒8 µm in length), one to five per valve, intercalate by other smaller and conical spines, one spine for every two interstriae. Linking valves with a flat face, perforated by marginal areolae that extend into the mantle through the marginal spines. Linking spines short, broadly spathulate with smooth edge, one spine for every two interstriae. Valve mantle usually ornamented by small knobs. Collum narrow, height 0.8‒1.1 µm. Pervalvar rows of areolae straight, 10‒16 in 10 µm. Areolae triangular close to marginal spines become rounded in the middle region of the mantle and elongate near the collum, 10‒15 in 10 µm, occluded by cribra. Ringleiste deep and thick, width1.6‒2.3 µm, protruding into the cell with reinforced rim. One to three rimoportulae above the inner side of the ringleiste. Other rimoportulae near the valve face/mantle junction in the separation and linking valves. External opening of rimoportulae associated with an areola, and not visible in LM. Internal opening of rimoportulae elongate and without stalk. Girdle bands with prominent ligula and finely perforated by round porous, ca. 10‒13 in 1 µm. Valvocopulae fimbriate. Auxospore with 12‒15 µm diameter., Published as part of Tremarin, Priscila Izabel, Ludwig, Thelma Alvim Veiga & Torgan, Lezilda Carvalho, 2014, Aulacoseira veraluciae sp. nov. (Coscinodiscophyceae, Aulacoseiraceae): a common freshwater diatom from Brazil, pp. 208-222 in Phytotaxa 184 (4) on pages 215-218, DOI: 10.11646/phytotaxa.184.4.2, http://zenodo.org/record/5146746

A new centric diatom genus is described from laminated freshwater sediments of Middle Eocene age near Horsefly, British Columbia, Canada. This diatom, Eoseira wilsonii gen. et sp. nov., grew in filaments that constitute dense monospecific sub-horizons within the white couplets that represent summer deposition in the varved sequence. Although Eoseira clearly belongs within the Family Aulacoseiraceae, several features distinguish its valve structure from Aulacoseira. Gigantism of spines and the lack of geometric relationships between spine position and mantle areolae are the most conspicuous features of the genus. Eoseira is among the oldest freshwater diatoms known and one of relatively few extinct freshwater genera. In addition to serving as a potential biostratigraphic marker, Eoseira is a cornerstone to undertanding the evolutionary trajectory of the Aulacoseiraceae, likely the oldest family of freshwater diatoms. As such, it refines our understanding of early radiations from the marine realm in western North America. Furthermore, paleoecological inferences based on Eoseira life strategy pertain directly to limnological conditions during early Cenozoic hot-house conditions.

Aulacoseira coroniformis Pearce & Cremer, sp. nov. (Figs 2 ��� 37) Frustula cylindrica, rectangularis in aspectu cinguli. Valvae circulares. Dimensiones valvarum: diameter discorum 6���15 ��m, limbus valvarum 4���8 ��m. Discus planus, tectus areolis aequaliter dispersis. Iunctura faciei valvae limbique leviter curvata. Striae limbi, 22���28 in 10 ��m, parallelae, continuantes in peripheriam faciei valvae. Areolae 35���45 in 10 ��m. Collum latum, sulcus distinctus, pseudoseptum latum praesens interius in limbo. Spinae marginales positae in iunctura faciei valvae limbique, in terminali omni vel fere omni costae pervalvaris. Rimoportula una observata in parte interna pseudosepti. Frustules cylindrical, rectangular in girdle view. Valves circular, 6���15 ��m in diameter. Pervalvar axis (mantle) 4���8 ��m in length. Discus flat with evenly arranged areolae. Valve face-mantle junction gently curved. Mantle areolae arranged in parallel rows (22���28 in 10 ��m), continuing onto the periphery of the valve face, 35���45 in 10 ��m. Collum broad, sulcus distinct, thick ringleiste present inside the mantle. Linking spines on each to every third mantle costa. One rimoportula at the inner side of the ringleiste. Type: ��� Highlands Hammock State Park, Sebring, Florida, U.S.A., 27��27���47.45������N, 81��32���21.48������W, Cleaned sediment from 74 cm depth from a 78 cm long sediment core (HHA 3), drilled on the 1 st of April 2008. Slide BR ��� 4199 (holotype BR, Figs 2���6). Habitat: ���Epiphytic in modern swamps; fossil in Holocene lake sediments. Distribution: ���Central Florida, U.S.A. Etymology: ���From the Latin corona (crown) and forma (form), referring to the crown-shaped appearance of the valve. Observations: ��� Valve outline and dimensions: The valve face is generally flat with a gentle transition towards the mantle (Figs 11���13). The discus-mantle boundary is difficult to recognize but usually characterized by a predetermined breaking line (arrows in Figs 12, 14 and 15) along which the discus regularly breaks (Fig. 12). The valve diameter is 6���15 ��m (mean 9 ��m; N = 48), the mantle height is 4���8 ��m (mean 5.5 ��m; N = 35) and the ratio of mantle height to diameter varies between 0.3 and 1.1 (mean 0.6; N = 35). Mantle: Approximately one quarter of the mantle height consists of the collum which possesses no areolae or other ornamentation. The boundary between the areolated mantle and the collum, the sulcus, is indicated as a local narrowing of the valve (arrows in Figs 3, 18). Areolae: The mantle striae consist of relatively small round (Figs 17, 18) to more or less rectangular (Figs 26, 27) areolae that are arranged in rows parallel to the pervalvar axis. The mantle striae density is 22���28 in 10 ��m (N = 18) and the areola density per stria varies between 35 and 45 in 10 ��m (N = 16). The striae continue over the mantle-valve face edge onto the periphery of the valve face (Fig. 11, 13). The discus itself is covered with mostly circular, evenly distributed areolae (Figs 14 ��� 16). The areola density on the discus is 98���108 areolae per 10 ��m 2 (N = 8). On the valve face, the line between the peripheral striae and the evenly arranged areolae in the centre marks the boundary between the discus and the mantle (Figs 11, 12, 14, 15; see also Krammer 1991a, p. 91). Vela, which are rather common in the genus Aulacoseira (Crawford & Likhoshway 2002) were not observed in the examined specimens of A. coroniformis. This could mean that the vela in A. coroniformis are too delicate to be preserved after acid-cleaning of the raw material. Ringleiste: The ringleiste is a thick bulge-like broadening (Figs 29���31) located inside the valve opposite from the sulcus, at the junction between the areolated mantle and the collum. The width of the ringleiste is approximately 10���15 % of the valve diameter (N = 6). Spines: At the junction of the mantle and the valve face, linking spines arise usually from a single pervalvar costa and are present on each to every third costa (Figs 17 ��� 22). Spines are usually straight, lacking any side spines and run parallel to the pervalvar axis. Spines vary considerably in shape being relatively long with blunt or pointed distal ends (Figs 17, 21, 22) or comparably shorter and club-shaped (Figs 26���28). Also spines having anchorshaped distal ends were observed (Fig. 11). The spine length ranges from 1.1���2.0 ��m (mean 1.6 ��m; N = 16). Separation valves with characteristic separation spines were not observed. Rimoportula: The labiate process is often difficult to recognize in Aulacoseira. A few valves of Aulacoseira coroniformis were observed having a rimoportula near the inner side of the ringleiste (Figs 32���37). The rimoportula is circular, stalk-less and surrounded by a thickened rampart-like siliceous wall (Figs 35, 37). Valves with more than one rimoportula were not observed. The external opening of the rimoportula which very often resembles a regular areola is difficult to recognize in A. coroniformis. The enlarged and somewhat isolated pores next to the sulcus visible in many valves (for example Figs 18, 22, 25) might correspond with the external rimoportulae openings. Likhoshway & Crawford (2001) provide an excellent overview on the variability of the morphology and position of rimoportulae in Aulacoseira., Published as part of Pearce, Christof, Cremer, Holger & Wagner-Cremer, Friederike, 2010, Aulacoseira coroniformis sp. nov., a new diatom (Bacillariophyta) species from Highlands Hammock State Park, Florida, pp. 40-48 in Phytotaxa 13 on pages 42-44, DOI: 10.11646/phytotaxa.13.1.3, http://zenodo.org/record/4778664, {"references":["Krammer, K. (1991 a) Morphology and taxonomy of some taxa in the genus Aulacoseira Thwaites (Bacillariophyceae). I. Aulacoseira distans and similar taxa. Nova Hedwigia 52: 89 - 112.","Crawford, R. M. & Likhoshway, Y. V. (2002) The velum of species of the diatom genus Aulacoseira Thwaites. In: John, J. (Ed.), Proceedings of the 15 th International Diatom Symposium, Perth, Australia, 28 September - 2 October, 1998. A. R. G. Gantner Verlag K. G., Ruggell, pp. 275 - 287.","Likhoshway, Y. V. & Crawford, R. M. (2001) The rimoportula - a neglected feature in the systematics of Aulacoseira. In: Economou-Amilli, A. (Ed.), Proceedings of the 16 th International Diatom Symposium, Athens & Aegean Islands, 25 August - 1 September, 2000. Amvrosiou Press, Athens, pp. 33 - 47."]}

Aulacoseira coroniformis sp. nov. is described from a short peat core recovered in Highlands Hammock State Park, Florida, U.S.A. The morphology of the new diatom species is documented by light and scanning electron micrographs and discussed in detail, including a comparison with related species in the genus Aulacoseira.