Moreneis cf. hexagona J. Park, Koh & Witkowski, 2012

Lobban, Christopher S. & Witkowski, Andrzej, 2023, Marine benthic diatoms of Guam: new records, Dictyoneis apapae sp. nov., and updates to the checklist, Micronesica 2023 (2), pp. 1-75 : 11

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 .

Figures

Figures 71–80. Moreneis, Nitzschia and Olifantiella. SEM except Fig. 71. Figs 71–74. Moreneis hexagona. Fig. 71. Valve in LM (DIC). Fig. 72. Valve exterior, showing isolated pores at the Voigt faults (arrows). Fig. 73. Valve exterior detail showing central raphe endings characteristic of the genus and c-shaped areolae. Fig. 74. Valve interior. Figs 75–78. Nitzschia incurva. Figs 75, 76. Guam voucher frustules at different angles. Figs 77, 78. Yap specimens showing interior and details of areolae. Figs 79, 80. Olifantiella mascarenica frustule showing the characteristic buciniportula (arrow). Scale bars: Fig 75 = 10 µm, Figs 71, 72, 74, 76, 77 = 5 µm, Figs 73, 78 = 2 µm, Figs 79, 80 = 1 µm.