Amphora micrometra Giffen (1967: 253)

Zidarova, Ralitsa, Pottiez, Margaux, Ivanov, Plamen, Haan, Myriam De & Vijver, Bart Van De, 2023, Amphora micrometra Giffen and Halamphora valdeminutissima sp. nov., two tiny benthic diatom species observed in the Black Sea, Phytotaxa 626 (3), pp. 199-207 : 204

Amphora micrometra Giffen (1967: 253) emend. Á cs, K.T.Kiss & Levkov in Á cs et al. (2011: 200)

( Figs 12–15, 20–21 )

References: — Snoeijs & Potapova 1995, p. 26, Ács et al. (2011), p. 200, figs 9–11, 30–34

LM observations ( Figs 12–15 ):— Valves narrowly semi-elliptic with moderately convex dorsal side and nearly straight ventral side, and rounded apices. Valve dimensions (n=6): 7.5–11.5 µm, width 1.5–2.0 µm. Raphe straight ( Fig. 15 ) or slightly arcuate ( Fig. 12 ), positioned close to the ventral side of the valve. Other morphological features not discernible in LM.

SEM observations ( Figs 20–21 ):— Due to the rarity of the species in the sample, only three valves were observed by SEM. Externally ( Fig. 20 ), valve face flat with a gradual transition between the valve face and valve mantle. Marginal ridge absent. Axial area very narrow, almost linear ( Fig. 20 , white arrows). Dorsal striae positioned between raised virgae, parallel to slightly radiate, ca 60 in 10 µm (n=3). Ventral striae parallel to weakly radiate, 70–80 in 10 µm (n=3). Finer areolar structure could not be resolved. Raphe straight, with straight, slightly expanded central raphe endings. Terminal raphe fissures could barely be observed (on Fig. 20 at right upper corner), hooked to the dorsal side. Internally ( Fig. 21 ), central raphe endings straight, terminating onto central fused helictoglossae ( Fig. 21 , black arrow). Terminal raphe endings straight, terminating onto very weakly developed helictoglossae ( Fig. 21 , grey arrow). A single portula present at each valve apex near the distal raphe ends ( Fig. 21 , white arrows).

Ecology and distribution:— Based on literature data listed in Ács et al. (2011), A. micrometra is a widely distributed species with records from all around the world under variable environmental conditions. However, without a careful morphological check, it is difficult to confirm all these records. In Europe, the species has been recorded with certainty in the Baltic Sea ( Snoeijs & Potapova 1995, Witkowski et al. 2000). The current observation seems to be the first verified record from the Black Sea. The species, observed at both studied sites (samples C3.1 and M4.3), was more rarely present in the samples compared to Halamphora valdeminutissima (Zidarova, pers. obs.).

Figures

FIGURES 2–21. LM and SEM microphotographs of Halamphora valdeminutissima sp. nov. and Amphora micrometra. 2–10. LM valve views of Halamphora valdeminutissima sp. nov. from the type population (sample C3.1, fig. 6 shows an entire frustule). 11. LM valve view of Halamphora valdeminutissima sp. nov. from a population near Maslen nos Cape (sample M4.3). 12–15. Amphora micrometra, LM views of several valves from the Black Sea, sample M4.3 (Figs 12–14) and sample C3.1 (Fig. 15). 16–18. Halamphora valdeminutissima sp. nov., SEM external views of entire valves, all from the type population (sample C3.1, Fig. 18 represents the holotype specimen). Fig. 16: white arrow indicates the dorsal raphe ledge; black arrow points to the thickening near the central raphe endings. Fig. 17: white arrow indicates the dorsal marginal ridge and black arrow indicates the small semi-elliptic central area on the ventral side. Fig. 18: black arrow points the thickening ventrally to the central raphe endings. 19. Halamphora valdeminutissima sp. nov., SEM internal view (type population, sample C3.1). Black arrow indicates the fused central helictoglossae, and white arrow points to the raphe fissures termination onto a weakly developed helictoglossa. 20. Amphora micrometra, SEM external view of a single valve from the Black Sea (sample M4.3). White arrow indicates the narrow axial area. 21. Amphora micrometra, SEM internal view of a valve from the Black Sea (sample M4.3). White arrows indicate the portulae at each valve apex; grey arrow points the terminal fissures; black arrow shows the fused central helictoglossae. Scale bars: 10 µm (2–15), 1 µm (16–21).