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 2024-06-06 2023 2 1 75 journal article 299061 10.5281/zenodo.12118784 2b921c3c-8618-439e-96da-1de9c66a90f9 0026-279X 12118784 Actinocyclus cuneiformis (Wallich) F. Gómez, Lu Wang & Senjie Lin Figs 1, 2 Basionym.: Hemidiscus cuneiformis Wallich Ref. illus.: Hustedt 1927 –1930, p. 904, fig. 542d; Ricard 1987 , Figs 30–34 ; the images in Round et al. 1990 , pp. 192–193, are also evidently this species; Gómez et al. 2017 , figs 1–23 Samples: GU66F-4 Dimensions: long axis 71–74 µm, short axis 41–45 µm Diagnostics: Distinctively shaped, lens-shaped in valve view but the frustules wedge-shaped (cuneiform) because the valve faces are at an angle to one another. Areolae with a series of radiating patterns around the margin, especially on the more strongly curved side. Large rimoportulae visible in the oblique view. A pseudonodulus is present on the flatter side. Comments: Two valves observed in one sample. The ventral curvatures of A. cuneiformis vary from straight to sinuous and Hustedt (1927 – 1931 ) combined several older Eudotia species as varieties. Although Round et al. (1990) say that the valves are cuneiform, it seems to us that Wallich’s (1860) epithet refers to the shape of the frustule (described by Round et al. 1990 as “shaped like orange segments”), rather than to the shape of the valve. The genus Hemidiscus was subsumed into Actinocyclus by Gómez et al. (2017) ; they did not discuss any varieties of H. cuneiformis but their images, like ours, conform to var. ventricosa (Castracane) Hustedt. We have therefore omitted any varietal designation.