Pteroncola marina Holmes & Croll

Lobban, Christopher S., 2015, 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), Micronesica 2015 (2), pp. 1-49 : 13

Pteroncola marina Holmes & Croll Figs 129, 130

FRAGILARIALES Silva : Fragilariaceae Greville

Ref. illus.: Holmes & Croll 1984, figs 2–15; Round et al. 1990, pp. 390–391, figs a–i

Samples: GU41D-A1; Jordan plankton tow Talofofo; black mangrove roots at Merizo (coll. Shiori Tamura)

Dimensions: Length 5.3–8.4 µm, width 2.6 µm; striae 75 in 10 µm

Diagnostics: Small tabulate frustules; exceedingly fine striae consist of very closely spaced pores (smaller than the apical pores); apical pores aligned conspicuously at 90° to the striae, as seen in girdle view. Thickened spots along edge of valve mantle.

Comments: The striae are alveolate, opening internally by single pores ( Round et al. 1990), as in Caloneis and Oestrupia ; Fig. 130 is consistent with this, and the pores can be seen through the external areolae. Round et al. (1990) proposed synonymy of P. marina and P. inane (Giffen) F.E. Round ( Dimerogramma inane Giffen 1970a , figs 20–22), which has elevated apices, but reexamination of Giffen’s materials in LM and SEM (A. Witkowski, personal communication) showed that P. marina is distinct. Almandoz et al. (2014) described a new species, P. carlinii Almandoz & Ferrario with much different striae, and also emended the genus description.

Figures

Figures 127–138. Figs 125–126. Psammodictyon pustulatum (GU66A-3) (SEM). Fig. 127. Oblique view of frustule showing linear pores on the dorsal valve face (arrow). In both Figs 127 and 128 the transition from the ventral to dorsal parts of the valvocopula is visible (arrowheads). Fig. 128. Apical view of frustule showing the distinctive topography of the ventral side of the raphe-keel, along with the linear pores on the dorsal side of the other valve (arrow) (two stacked images). Figs 129, 130. Pteroncola inane (SEM). Fig. 129. Frustule in girdle view (GU41D-1A). Fig. 130. Broken frustule showing internal and external valve faces, with the single row of internal pores (arrows) (Jordan collection, image by Misaki Ishizawa) (SEM). Figs. 131–138. Rhoiconeis pagoensis. Figs 131, 132. Same live cell in valve and girdle view showing plastids (GU7X-8) (DIC). Figs 133, 134. Holotype (valve view) and a girdle view from the same slide (GU7X-7) (DIC). Fig. 135. Frustule in valve view (GU7X-7) (SEM). Fig. 136. Frustule in girdle view; note the very short striae at the central area on the concave valve (GU7X-2) (SEM). Fig. 137. Detail of a pair of frustules showing difference in striae lengths at central area on convex and concave valves (GU7X-2) (SEM). Fig. 138. Apex of a frustule in girdle view showing the segmented valvocopula (S1 and S2) and two pleural bands (P1 and P2) (GU7X-5) (SEM). Scale bars: Fig. 136 = 10 µm, Figs 127–128, 131–135 = 5 µm, Figs 129, 130, 137, 138 = 2 µm.