Halamphora baleenicola

Description.—LM morphology: Valves semielliptical, strongly dorsiventral (Figs. 66–71). Dorsal margin broadly arched. Ventral margin slightly concave. Valve apices rounded, slightly protracted in some specimens. Valve length 43–64 μm, valve width 9–13 μm, n > 351. Raphe weakly arched. Central raphe endings positioned close to each other, dilated, dorsally deflected. Polar raphe endings dorsally deflected. Axial area narrow. Dorsal striae finely areolate, parallel near the valve center, becoming slightly radiate near apices. Stria pattern interrupted at valve middle with appearance of coarser striae and increased areola spacing. Dorsal stria density 28–31 in 10 μm, n = 31. Ventral portion of valve narrow with fine striae difficult to resolve in LM (Figs. 66–71). SEM morphology: Externally, dorsal stria areolae vary in size, shape, spacing. Areolae small, circular to transapically elongated, oblong (Figs. 72–75). Dorsal areolae irregularly spaced near valve middle (Fig. 73) due to silica infilling of areolae. Ventral striae consisting of 2-3 rows of small areolae, finer and more closely spaced than dorsal striae; stria density 37–43 in 10 μm, n = 15 (Figs. 74–75). Ventral striae more or less interrupted at valve middle with some specimens exhibiting a distinct unornamented area (Fig. 73). Dorsal marginal ridge absent (Fig. 72). Central raphe endings positioned close to each other, slightly deflected, dilated dorsally (Fig. 73). Polar raphe endings slightly deflected dorsally, partially obscured by raphe ledge (Fig. 75). Dorsal raphe ledge continuous, more fully developed near apices and valve center (Figs. 72–74). Ventral raphe ledge absent. Internally, areolae occluded by hymenes (Fig. 77). Internal raphe-sternum elevated from valve surface on dorsal side (Figs. 76–78). Flange-like structure projecting towards cell interior from the dorsal raphe-sternum at central nodule (Fig. 77). Polar raphe endings as very weakly developed helictoglossae (Fig. 78). Complete cingula not observed, but separated copulae open, broader dorsally than ventrally, with 2 rows of slit-like areolae separated by unperforated area that is thickened on one side of band (Fig. 79). Copula areolae
density 39–45 in 10 μm. 

Diagnosis.—Observed in the LM, Halamphora baleenicola shares features with several widely distributed marine members of the genus Amphora, including Amphora acuta W.Gregory, Amphora arcuata A.W.F.Schmidt, Amphora abludens Simonsen, and Amphora subhyalina Podzorski and Håkansson. These taxa all share a similar valve outline, a more or less straight and ventrally appressed raphe, areolate striae, thickened central virgae, and rounded apices. This taxon is distinguished from A. acuta by its smaller size and finer striae, with Levkov (2009) reporting valve length of A. acuta as 80–140 μm, width as 20–30 μm, and stria density as 14–16 in 10 μm. A. arcuata is differentiated by its distinct biarcuate ventral margin and acute apices. Both A. abludens and A. subhyalina are smaller taxa with finer striae. Stepanek and Kociolek (2018) report valve length as 14–35 μm, width as 4.0–5.5 μm, and stria density as 50–53 in 10 μm for A. abludens and valve length as 26–43 μm, width as 5.0–5.5 μm, and stria density as 42–43 in 10 μm for A. subhyalina (reported as A. insulana, synonym). For A. subhyalina, Podzorski and Håkansson (1987) report valve length as 21.3 μm, width as 5.3 μm, and stria density undiscernible in LM and Lobban and Witkowski (2023) report valve length as 27–45 μm, width as 7–8 μm, and stria density as 36–39 in 10 μm. Additionally, H. baleenicola lacks the continuous dorsal marginal ridge often visible in all of these Amphora species (Levkov, 2009, Stepanek and Kociolek, 2018).

• Author
  Stepanek, M.J.Sullivan and Frankovich 2026
• Length Range
  43-64 µm
• Width
  9-13 µm
• Striae in 10µm
  37-43 (dorsal stria density), 37-43 (ventral stria density)