Amphora subhyalina Podzorski & Håkansson Figs 5–7

Syn.: Amphora insulana Stepanek & Kociolek

Ref. illus.: Podzorski & Håkansson 1987, p. 52; pl. 15, fig. 10, pl. 51, figs 7, 8; Stepanek & Kociolek 2018, p. 14, pl. 5, figs 13–16, pl. 8, figs 1–4.

Samples: GU44Y-13, GU44Z-15, GU52Q-1a, GU66G-2, GU68A-2

Dimensions: Length 27–45 µm, width 7–8 µm; dorsal striae 36 in 10 µm in the middle increasing to 39 toward the apices, ventral striae 38 in 10 µm.

Diagnostics: Valves and copulae frequently forming a hyaline oval pattern in LM. In SEM, more prominent elongated areolae on either side of the dorsal rib with the rest of the dorsal striae comprising small areolae; prominent conopea at the central raphe endings.

Comments: As far as we can tell from the SEM illustrations of valves in Podzorski & Håkansson (1987) and Stepanek & Kociolek (2018), the same species is being described and therefore the former name has priority. Although clearly shown in SEM by Stepanek & Kociolek (2018), they did not include a written description of ultrastructure. Podzorski & Håkansson (1987), although showing SEMs, also did not specify stria densities. Our SEM images show dorsal striae of irregular transapical slits, ending with a long, prominent slit at valve margin, mantle sharply delimited by a ridge and bearing a similar series of prominent slits (Figs 6, 7). Small central area on dorsal side of central nodule, and central striae somewhat more prominent. Ventral valve face with single row of slit-like areolae, interrupted by a conopeum developed ventrally and the ventrally deflected raphe. Internally, as shown in Stepanek & Kociolek (2018, pl. 8, fig. 4) the proximal raphe endings are straight. The girdle bands have a single line of slits along the narrow ventral part and faint striae on the wide dorsal part (Fig. 7 arrow). The lack of a ventral raphe ledge is indicative of Halamphora rather than Amphora, as summarized by Stepanek & Kociolek (2018, pp. 8–9 vs 28–29), but the broad girdle bands are indicative of Amphora. Neither Podzorski & Håkansson (1987) nor Stepanek & Kociolek (2018) showed girdle bands. Their materials were, respectively, from Palawan (Philippines) and Florida Keys.

These fairly large, hyaline frustules resemble Halamphora hyalina (Kützing) Rimet & R.Jahn (Rimet et al. 2018) and Halamphora pseudohyalina (Simonsen) Stepanek & Kociolek (2018) (neither yet recorded from our region) in the presence of the distinct central area and a ventral surface; H. pseudohyalina has fine dorsal striae 28–30 in 10 µm barely distinguished in LM and ventral striae ca 65 in 10 µm, whereas as H. hyalina and A. vaughanii Giffen have clearly visible striae, 20–23 in 10 µm and 28–30 in 10 µm, respectively. Amphora hyalina, reported from Yap by Navarro & Lobban (2009, figs 97, 98), has an exposed, dorsally deflected raphe with a conopeum extending dorsally on the dorsal raphe ledge; the striae are finely biseriate, the areolae consistently small, apicallyelongated slits. Amphora vaughanii was recorded from Guam (Lobban et al. 2012, pl. 56, figs 7–9), it has biseriate striae of very fine pores on the dorsal surface and a line of very closely spaced slits on the mantle, conopea absent; its position in Halamphora or Amphora has not yet been considered.