A new small-celled diatom from Brazil - Luticola minutissima sp. nov., with comparison to the type of the Antarctic L. neglecta Zidarova, Levkov & Van de Vijver Author Rybak, Mateusz 0000-0001-8998-9537 matrybak 91 @ gmail. com; https: // orcid. org / 0000 - 0001 - 8998 - 9537 matrybak91@gmail.com Author Peszek, Łukasz 0000-0002-9132-2210 lpeszek @ ur. edu. pl; https: // orcid. org / 0000 - 0002 - 9132 - 2210 lpeszek@ur.edu.pl Author Skoczylas, Łukasz 0000-0002-6650-811X Uniwersytecki Szpital Kliniczny im. J. Mikulicza-Radeckiego we Wrocławiu, ul. Borowska 213, 50 - 556 Wrocław, Poland & lukasz. skoczylas 93 @ gmail. com; https: // orcid. org / 0000 - 0002 - 6650 - 811 X lukasz.skoczylas93@gmail.com Author Ludwig, Thelma Alvim Veiga 0000-0003-0576-3499 Botany Department, Universidade Federal do Paraná, Centro Politécnico, Paraná, CP 19031, CP 81531 - 990, Jardim das Américas, Curitiba, PR, Brazil & veiga 13 ufpr @ gmail. com; https: // orcid. org / 0000 - 0003 - 0576 - 3499 veiga13ufpr@gmail.com text Phytotaxa 2022 2022-01-11 530 3 287 294 journal article 2669 10.11646/phytotaxa.530.3.4 7754a63a-2c48-4b81-ae27-55f6f3ee8db1 1179-3163 5836017 Luticola minutissima M. Rybak, Peszek, Skoczylas & Ludwig , sp. nov. ( Figs 1–46 ) Type:— BRAZIL . Rio de Janeiro : city of Rio de Janeiro , Alto da Boa Vista , 22°57’09’’S , 43°13’40’’W , Ł. Skoczylas , 29 March 2015 ( holotype UPCB ! slide UPCB96.149 , Herbarium of the Departamento de Botânica da Universidade Federal do Paraná , Brazil , depicted in Fig. 19 ). Isotypes : slide 26943 at the Szczecin Diatom Collection hosted by the University of Szczecin ( SZCZ ); slide 2015/1/1 and cleaned material stored in the Diatom Collection of the Institute of Agricultural Sciences , Land Management and Environmental Protection at the University of Rzeszów . Description:— Valves elliptic-lanceolate to rhombic-lanceolate with narrowly rounded apices ( Figs 1–37 ). Range of valve dimensions (n = 60): 5.2–16.8 μm long and 3.7–5.4 μm wide. Axial area linear, central area bow-tie shaped, bounded by 2–4 areolae. Elongated stigma present in the central area, located close to face valve margin ( Figs 38, 40, 42 ). Internally, stigma with indistinct opening bordered with large, circular, and lipped structure ( Fig. 43, 45, 46 ). Marginal channel evident in SEM ( Fig. 46 ), not visible in LM. Raphe branches almost straight to slightly curved ( Figs 1–37 , 39–41 ). External proximal endings double curved, first deflected away from the stigma, next abruptly hooked at a 90-degree angle to the stigma side ( Fig. 29–42 ). Distal raphe endings hooked towards the stigma side, continuing onto the valve mantle ( Fig. 39–42 ). Striae radiate, 22–28 at 10 μm, composed of 3–4 rounded areolae. Internally, poroids on valve face occluded by hymens, forming a continuous strip on each stria ( Fig. 44, 46 ). Valve mantle has a single row of round areolae ( Fig. 30, 37 ). Etymology:— The species name minutissima (lat. –tiny, smallest) refers to the small size of the new species’ frustule. FIGURE 1–37. Luticola minutissima sp. nov . Fig. 19. holotype specimen, LM. 1–28 Valves in size diminution series, LM. 29–37 Valve exterior, SEM. Scale bars = 10 μm (Figs 1–28); 5 μm (Figs 29–31, 35-37); 4 μm (Figs 32–34). Similar species:— Luticola deniseae Wetzel, Van de Vijver & Ector (2010: 178) , L. imbricata (W.Bock) Levkov, Metzeltin & Pavlov (2013: 134) , L. minima Levkov, Metzeltin & Pavlov (2013: 157) , L. neglecta Zidarova, Levkov & Van de Vijver and L. tujii Levkov, Metzeltin & Pavlov (2013: 243) , ( Table 2 ). Distribution and ecology:— The species was observed in terrestrial habitats (mosses and lichens overgrowing different substrates, i.e. a concrete wall and palm tree trunks), both in urban and forest areas. The species developed very rarely, in the form of individual valves in the samples. Together with Luticola minutissima sp. nov. , the most frequent species in sample 2015/1 were Humidophila sp. (90.3%) and Achnanthes pseudoinflata M.Rybak, Peszek, Skoczylas, Ector & C.E.Wetzel (2020: 3) (7.4%), while in sample 2015/3 the most frequent were: Humidophila contenta (Grunow) Lowe, Kociolek, J.R.Johansen, Van de Vijver, Lange-Bertalot & Kopalová (2014: 357) (74.8%) and Luticola moreirae Straube, Tremarin & T.Ludwig (2017: 428) (17.9%). In sample 2015/2 no dominant species were designated, due to an extremely low number of valves (15–30 per slide). FIGURE 38–46. Detailed SEM close-ups of Luticola minutissima sp. nov . 38, 42 External detail of proximal raphe endings and stigma. 39–41 External detail of areolae and raphe branches with distal endings. 43–45 Valve face, internally. 46 Internal view of stigma, proximal raphe endings and areolae covered by hymenes. Scale bars = 2 μm (Figs 38–42); 5 μm (Figs 43–45); 1 μm (Fig. 46). TABLE 2. Comparison table of Luticola minutissima sp. nov. and similar Luticola taxa.

Taxon	L. minutissima sp. nov.	L. neglecta	L. deniseae	L. tujii	L. minima	L. imbricata
Length (µm)	5.2–16.8	7–18	11–29.5	14–23	9–19	(7)10–23(34)
Width (µm)	3.7–5.4	4–5.5	3.5–7	5–6.5	4–5.5	5–7(9)
Striae (in 10 µm)	22–28	21–26	21–28	22–28	21–24	18–22
Areolae (per striae)	3–4	2–3	3–4	3–5	1–2	3–4
Proximal raphe endings	abruptly hooked	weakly deflected with irregular thread-like shallow depressions	clearly deflected	slightly deflected	slightly deflected	short, deflected
Distal raphe endings	hooked	hooked	hooked	hooked	hooked	hooked
Geographical distribution	South America	Antarctic	South America	Asia	Africa	Europe
Habitat preferences	aerophytic on wet mosses	soils and dry mosses	epizoic on freshwater turtle	springs	Lake Tanganyika	aerophytic, wet rocks, soils
References	this study	Zidarova et al. (2014)	Wetzel et al. (2010)	Levkov et al. (2013)	Levkov et al. (2013)	Levkov et al. (2013 , 2017)

Additional observation of Luticola neglecta Zidarova, Levkov & Van de Vijver is presented ( Figs 47–67 ). The observed valves (n = 30) correspond to the description in Zidarova et al. (2014 , 2016 ) in most morphological features. Notwithstanding, some additional observations were made. The external shape of stigma in the mentioned papers is small and rounded, but from our observations, it also seems to be slightly elongated ( Figs. 61, 63, 64 ). The internal valve view ultrastructure has not been described until now. The areolae of the valve face are occluded by hymenes, forming a continuous strip on each stria. A marginal channel is visible internally under SEM, and is occluded by hymen. Internal stigma opening is small and C-shaped.