Encyonopsis sp. 1

Kennedy, Bryan, Buckley, Yvonne & Allott, Norman, 2019, Taxonomy, ecology and analysis of type material of some small Encyonopsis with description of new species in Ireland, Phytotaxa 395 (2), pp. 89-128 : 107

Encyonopsis sp. 1 ( Figs 246–287 )

Description: Valves weakly dorsiventral, linear to linear-lanceolate in outline with weakly convex to sublinear dorsal and ventral sides, smaller forms are more lanceolate. Poles are rounded capitate to subcapitate, with or without clear shoulders. Axial area very narrow and central area absent. Length 10.4–15.8 μm; width 2.9–3.8 μm; maximum L:W ratio 5.3. Average stria density only slightly higher dorsally (30 in 10 μm) than ventrally (29 in 10 μm) with shortened or bent striae often found at valve centre. Raphe filiform, curved more ventrally with proximal ends bent to dorsal side. Areolae are small oval to peanut shaped.

This form has an equivalent ultrastructure to E. aff. tavirana with a slightly expanded terminal fissure, comparable shaped puncta and dorsal stria density. It lacks the very robust outline and distinctive shoulders and has a higher maximum L:W ratio (L/W=5.3 versus 4.3). These features usually allow for a clear separation from that species in LM. Average valve width in the type population of E. tavirana is higher than this form, but maximum L:W ratio is equivalent. This diatom also closely resembles E. alpina in LM but slightly coarser, angled orientation of stria at central area and a lower average L:W ratio is usually sufficient to separate most populations of these diatoms.

Ecology: This form is most likely to have been misidentified as E. alpina in the past. Individual frustules are occasionally difficult to differentiate and both frequently co-occur. It is a widespread diatom found in 43 lakes and reaches a high relative abundance in epilithic habitat (max.= 71%). It has a relatively broad tolerance across the alkalinity gradient but a low optimum for TP, which is equivalent to populations of E. tavirana and E. alpina but significantly different (p<0.01) from E. aff. tavirana .

Figures

FIGURES 246–287. Encyonopsis sp. 1 Figs 246–287. LM. Figs 246–281. Valves showing morphological range and size variation in populations. Figs 282–287. SEM. Figs 282–285. External view. Figs 286–287. Internal view. Scale bar in Fig. 257 = 10 μm for all LM figures. Scale bar in all SEM micrographs = 1 μm.