Marine benthic diatoms of Guam: new records, Dictyoneis apapae sp. nov., and updates to the checklist Author Lobban, Christopher S. Division of Natural Sciences, University of Guam, Mangilao, GU 96923, USA clobban @ triton. uog. edu clobban@triton.uog.edu Author Witkowski, Andrzej University of Szczecin, Institute of Marine and Environmental Sciences Mickiewicza 16 a, PL 70 - 383 Szczecin, Poland text Micronesica 2023 2023 2 1 75 journal article 10.5281/zenodo.12118784 0026-279X 12118784 Moreneis cf. hexagona J. Park, Koh & Witkowski Figs 71–74 Ref. illus.: J . Park et al. 2012 , p. 192, fig. 6; J . S . Park et al. 2018 , p. 108, fig. 26. Samples: GU 52O-4, GU 44AS-4 Dimensions: Length 31–32 µm, width 13 µm; striae 15 in 10 µm, areolae 16 in 10 µm. Diagnostics: Central and terminal raphe endings deflected in same direction, central endings in opposite directions ( Fig. 73 ), distinguish the genus from Petroneis and Navicula . Species based on shape, dimensions, and stria density. Valve rostrate; striae radiate, some shorter ones in center. Comments: Rare specimens match the description of M. hexagona , which is smaller and more finely striated than M. angulata (42–48 µm x 16–16.5 µm, striae 11 in 10 µm, areolae 12 in 10 µm). J . Park et al. (2012) noted a single areola at the Voigt faults ( Fig. 72 , arrows) and larger areolae adjacent to axial area, which are present in our specimen. Our SEM images are the first for this species and show the areolae to be c-shaped ( Fig. 73 ). Moreneis hexagona is distinguished from several other species by shape and stria density. J . S . Park et al. (2018) reported M. cf. hexagona from Chuuk with some hesitation because of a size difference. Present in biofilm with another Moreneis sp. in GU 52O-4, but also found in a gathering of Halimeda in GU 44AS-4. The other species does not match any of the species in this newly erected genus but it may have been described under Navicula .