Description of five new Luticola D. G. Mann (Bacillariophyta, Diadesmidaceae) species from Indonesia with comments on the morphological boundaries of the genus Author Rybak, Mateusz https://orcid.org/0000-0001-8998-9537 Department of Agroecology and Forest Utilization, University of Rzeszow, ul. Cwiklinskiej 1 A, 35 - 601 Rzeszow, Poland matrybak91@gmail.com Author Peszek, Lukasz https://orcid.org/0000-0002-9132-2210 Department of Agroecology and Forest Utilization, University of Rzeszow, ul. Cwiklinskiej 1 A, 35 - 601 Rzeszow, Poland Author Luthfi, Oktiyas Muzaky https://orcid.org/0000-0002-9550-9381 University of Brawijaya, Department of Marine Science, Malang, East Java, Indonesia & Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA Author Arsad, Sulastri https://orcid.org/0000-0002-7322-7834 University of Brawijaya, Department of Marine Science, Malang, East Java, Indonesia & Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA Author Kociolek, John Patrick https://orcid.org/0000-0001-9824-7164 University of Szczecin, Institute of Marine and Environmental Sciences, Mickiewicza 16 A, 70 - 383 Szczecin, Poland Author Witkowski, Andrzej https://orcid.org/0000-0003-1714-218X Museum of Natural History and Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA text PhytoKeys 2024 2024-01-05 237 1 22 http://dx.doi.org/10.3897/phytokeys.237.113773 journal article http://dx.doi.org/10.3897/phytokeys.237.113773 1314-2003-237-1 73137075AF5A5E78890C5807B27C71AB Luticola insularis M.Rybak & Peszek sp. nov. Figs 1A-S , 4A-H Description. LM observations (Fig. 1A-S ). Valves elliptic-lanceolate to lanceolate with narrowly rounded apices. Range of valve dimensions (n = 35): 8.5-24.0 μm long, 4.5-7.0 μm wide and 16-20 striae in 10 µm . Striae clearly punctate, composed of 3-4 areolae. Central area rectangular to slightly bow-tie shaped axial area linear and narrow Isolated pore clearly visible in central area located halfway between the margin and the centre. Raphe filiform with proximal endings slightly bent away from isolated pore, distal raphe endings barely visible. Figure 1. LM microphotographs of three new Luticola taxa in size diminution series. Luticola insularis sp. nov. ( A-S ), Luticola bandanensis sp. nov. ( T-AC ), Luticola eliptica sp. nov. ( AD-AN ). Scale bar: 10 µm . SEM observations (Fig. 4A-H ). External view : Striae composed of 3-4 areolae round, becoming larger and more elongated near the margins (Fig. 4A-E ). Single row of elongated areolae, interrupted at valve apices, present on valve mantle (Fig. 4D, F ). Central area bordered by 2-3 areolae (Fig. 4A-D ). Raphe filiform with weakly hooked distal ends continuing on to valve mantle (Fig. 4A, C-E ). Proximal raphe ends slightly bent opposite to the isolate pore bearing side, then shortly hooked to the pore and finishing with a small, elongated shallow depressions (Fig. 4B, D, E ). Opening of isolated pore small and slightly elongated (Fig. 4A-D ). Girdle bands open with two rows of poroids (Fig. 4D, F ). Distinct silica ridge visible along valve face/mantle junction (Fig. 1D, F ). Internal view : Areolae occluded by hymenes forming a continuous strip (Fig. 4G, H ). Raphe slits straight (Fig. 4G, H ). Proximal raphe endings simple and straight (Fig. 4G, H ), distal raphe endings finishing on to weakly developed helictoglossae (Fig. 4G, H ). Isolated pore opening with small lipped structure (Fig. 4G, H ). Longitudinal channels visible along valve (Fig. 4G, H ). Type . Indonesia , Banda Besar, 4°31'29.93"S , 129°56'51.69"E , 19 m a.s.l. , coll. 23 June 2018 , holotype slide no. SZCZ29103! and the unmounted material with the same number in the Szczecin Diatom Collection ( University of Szczecin , Poland ), isotype slide no. 2018/440 and the unmounted material with the same number at the University of Rzeszow , Poland . The type population is illustrated in Figs 1A-S , 4A-H . Etymology. The name refers to the fact that the species was found on one of many Asian islands (lat. insula - island). Distribution. So far, this species has been observed only in the type locality. Ecology and associated diatom flora. The species was observed in a sample characterised by a slightly acidic pH (5.8) and conductivity was 1250 µS /cm. The species described herein co-occurred with: Luticola bandanensis sp. nov., L. elliptica sp. nov., L. minima Levkov, Metzeltin & Pavlov, two unidentified small-celled Nitzschia sp., Nitzschia vitrea G.Norman and Tryblionella debilis Arnott ex O'Meara .