Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis) Lobban, Christopher S. Micronesica 2015 2015 2 1 49 Grunow Grunow 1880 [232,553,1353,1378] Bacillariophyceae Menoponidae Nitzschia CoL Chromista Psocodea 8 9 Ochrophyta species janischii  Samples: GU44Z-15, GU44AK-2, GU44AR-2 Dimensions: Length 225–275 µm, width 7–9 µm; striae 23 in10 µm; fibulae 4 in10 µm Diagnostics: Extremely long valves with irregularly spaced fibulae extending completely across the valve face. Central nodule present ( Fig. 86). Areolae arranged in quincunx pattern of transapical and diagonal striae. Fourteen large, platelike plastids observed, with large pyrenoids ( Fig. 83). Comments:  N. janischiiis most similar to  Tryblionella scalaris(Ehrenberg) Siver & Hamilton[=  N. scalaris(Ehrenberg) W. Smith] (Ruck & Kociloek 2004, pl. 62–65), but that primarily freshwater/brackish species has ribs that extend only halfway across the valve face, besides the characters that make it  Tryblionella.  N. janischiiwas not recorded from The Bahamas( Hein et al. 2008), Puerto Rico( Hagelstein 1939, Navarro 1983b), Mahé( Giffen 1980), or Tahiti ( Ricard 1977), and we are aware of no record other than Grunow’s. No ultrastructure images are cited in  Gaulet al. (1993)or Henderson & Reimer (2003). Grunow (1880)illustrated only half of a specimen from the Hawaiian Islands, where it was “rare,” but Peragallo & Peragallo (1897–1908) drew a whole valve; it is not clear whether they saw Grunow’s specimen, as they mention it only as a “curious exotic form,” perhaps not in the French flora. Grunow placed his species in Section Epithemioides, rather than Subgenus  Denticula, but the differences are ill-defined.  Denticulais now regarded as a separate genus, and Round et al. (1990, p. 622) commented that  Denticulais, “Closely related to  Nitzschiasect. Grunowia, from which it is difficult to separate, except on the extent of the fibulae.” In  Denticulaall the fibulae “extend across the valve face, forming partitions running from margin to margin. The fibulae widen at their bases (near the raphe) so that only small apertures (‘portulae’) are left connecting cell interior with subraphe canal.” This is also true of  N. janischii, yet fibulae reaching the valve margin is not a synapomorphy for  Denticulabecause a few other  Nitzschiaspeciesalso have this character, e.g.,  N. rhopalodioidesHustedt( Hustedt 1955, p. 45, pl.15, fig. 16), and even  N. ventricosaKitton( Lobban et al. 2012, pl. 61, figs 1, 2), although there, as in  Gomphonitzschia cleveiGrunow( Grunow 1880, pl. 14, fig. 11, Peragallo & Peragallo 1897–1908, pl. 76, fig. 15), some extend only part way and some costae extend part way back from the margin. At present there does not seem to be justification for reclassifying  N. janischiiin  Denticula.