Halamphora valdeminutissima Zidarova, Pottiez, P.Ivanov, M.de Haan & Van de Vijver, 2023

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 : 202

Halamphora valdeminutissima Zidarova, Pottiez, P.Ivanov, M.de Haan & Van de Vijver , sp.nov.

( Figs 2–11, 16–19 )

Description

LM observations ( Figs 2–11 ):— Valves semi-lanceolate with distinctly convex dorsal margin ( Figs 2–10 ) and straight ( Fig. 2 ) to slightly convex ( Figs 7, 9 ) ventral margin, occasionally slightly concave in the middle ( Fig. 3 ). Valve apices small, protracted, subrostrate, bent toward the ventral side. Valve dimensions (n=14): length 6.0–13.5 µm, width 1.5–3.0 µm. Raphe slightly arcuate, located almost centrally along the vertical axis of the valve, slightly closer to the ventral side. Other characteristic features difficult to discern in LM. Valves from a second small population (sample M 4.3) had the same characteristics ( Fig. 11 ).

SEM observations ( Figs 16–19 ):— Externally, valve face flat with a small marginal dorsal ridge (indicated on Fig. 17 , white arrow) interrupting the striae at the valve face/mantle junction ( Figs 17, 18 ). Dorsal striae ca 45 in 10 µm (n=7), parallel to weakly radiate towards the apices, usually composed of a single elongated areola on the valve face and a single areola on the mantle ( Fig. 17 ). Areolae possessing recessed foramina between relatively thick virgae. Occasionally, irregularities in this striation pattern were observed ( Fig. 16 ). Ventral striae 55–65 in 10 µm (n=7), composed of a single areola with recessed foramina, parallel to slightly radiate, distinctly shorter near the valve middle, where slightly arched in the center, and leaving a small semi-elliptic central area on the ventral side ( Fig. 17 , black arrow). Distinct raphe ledge present along the entire length of the valve on the dorsal side (indicated on Fig. 18 , white arrow), slightly widening at the valve middle, then running straight, weakly widening once again towards the apices, and finally gradually narrowing at the apices (see Figs 16–18 ). Small thickening present on the ventral side near the central raphe endings ( Figs 16, 18 , black arrow). Raphe slightly arcuate, central raphe endings close one to another, drop-like enlarged and shortly bent towards the dorsal side ( Figs 16–18 ). Distal raphe fissures weakly dorsally deflected ( Figs 16–18 ). Internally ( Fig. 19 ), striae located between slightly raised virgae. Central raphe endings terminating onto fused helictoglossae ( Fig. 19 , black arrow), and terminal raphe endings terminating onto small helictoglossae ( Fig. 19 , white arrow). Finer areolar structure externally and internally not resolved.

Type— BULGARIA. The Black Sea: Sozopol Bay, south of Marina Port Sozopol , 42°25’05.3”N, 27°41’20.6”E. Sample C 3.1, Leg. R. Zidarova & P. Ivanov, 30 August 2020 (holotype: stub BR-4804! in BR Collection, Meise Botanic Garden Meise, Belgium. Fig. 18 represents the holotype specimen. Additionally, cleaned material of sample C 3.1 is stored at BR Collection, Meise Botanic Garden, Belgium).

Registration: — http://phycobank.org/104178

Etymology:— The specific epithet “valdeminutissima ” refers to the very small valve dimensions of this species.

Ecology and distribution:— So far, the species has only been observed during summer months off the southern Bulgarian Black Sea coast, both near Marina Port Sozopol (sample C 3.1) and Maslen nos Cape (sample M 4.3). At both sites, sea water temperature was around 26 oC, sea water pH was around 8.3, and salinity and conductivity values were ca 18 PSU and ca 29 mS/cm, respectively, and these values showed very little variations during the entire month of measurements ( Table 1 ). The type locality is characterized by deteriorated oxygen conditions, but excellent condition with regard to inorganic forms of nitrogen and in good state in terms of phosphorous concentrations, according to the local regulations ( Zidarova et al. 2022). Full record of measured environmental variables at the type locality are given in Zidarova et al. (2022, Table 1 ).

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).