Encyonopsis tavirana Krammer, 1997

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 tavirana Krammer ( Figs 178–200 )

Description: Valves weakly dorsiventral, linear to linear-lanceolate in outline with very weakly convex dorsal and ventral sides, smaller forms are more lanceolate. Poles are relatively broadly rounded capitate, dorsally and ventrally with clear shoulders or indication of shoulders in larger valves, smaller forms without shoulders. Axial area very narrow and central area absent. Length 10–18.9 μm; width 3.4–4.2 μm; maximum L:W ratio 5.1. Average stria density slightly higher dorsally (30.5 in 10 μm) than ventrally (29 in 10 μm) but have a higher range than given with the diagnosis when re-measured (29–32 in 10 μm dorsally and 26–30 in 10 μm ventrally). Raphe filiform, curved more ventrally with proximal ends bent to dorsal side. Areolae are more distinctly bent or peanut-shaped relative to comparable taxa. A combination of characters can be used to separate the more robust valves of E. tavirana from others including, a linear lanceolate outline with robust valves having very well-developed shoulders, a greater maximum valve width, clearly capitate broadly rounded poles, and approximately 30 transapical striae or less in 10 μm.

Populations of a diatom closely resembling E. tavirana from Irish lakes are comparable in morphology, including broadly capitate valves and poles, distinct shoulders and relatively fine striae. But average valve width and maximum L: W ratio (4.3 versus 5.1) are lower relative to the type population. This species is likely to have been frequently confused with E. microcephala in the past, given their similar robust outline and equivalent valve width. However, ultrastructural characteristics clearly differ from the type population of E. microcephala illustrated in Krammer 1997b. Distal raphe endings are more gently deflected over the apices and terminate in a small rounded pore in the latter taxon. Internally the clearly constricted alveoli and lower stria density (23–25 in 10 μm) are also differentiating.

Ecology: Originally found in the Portuguese Algarve and abundant in wells, mountainous regions and oligotrophic waters with high oxygen content. Irish populations with an affinity to E. tavirana occur in 13 lakes with a maximum relative abundance of 47%. It occurs in more eutrophic lakes and has a higher nutrient optimum relative to the type population or compared to others in the microcephala -complex, suggesting a diatom sensitivity score S=3 for lake ecological assessment ( Fig. 532–533 ).

Figures

FIGURE 532. Scatter plots of the distribution of Encyonopsis taxa in relation to A. Total phosphorus (TP) and B.Alkalinity. Vertical lines indicate the location of optima derived from weighted averages of species occurrences for TP (red) and alkalinity (blue). Taxon codes correspond to Fig. 530, with All (ENCY All) and Unidentified (ENCY unid.) Encyonopsis categories illustrated for comparison.

FIGURE 533. NMDS biplot of Bray-Curtis dissimilarity matrix of untransformed relative abundance of Encyonopsis in lake periphyton samples. Inset is a plot of lakes with significant environmental factors (p<0.05) fitted a posteriori, including true colour (TC), chlorophyll a (chla), total phosphorus (TP), total oxidised nitrogen (TON), silica (Si), total ammonia (NH4), conductivity (cond), alkalinity (alk) and pH. Main plot shows the location of Encyonopsis species added as weighted averages of site scores with surface contour plots for TP (red curves) and Alkalinity (blue curves) gradients fitted a posteriori.

FIGURES 178–200. Encyonopsis tavirana Krammer Typus: Prap. 517B IOK. Figs 178–192. LM. Figs 178–192. Valves showing range of morphological variability and variation in type population. Figs 193–200. SEM. Fig. 193. External view. Fig. 194. Internal view. Figs 195–199. SEM showing variation in outline and apices in type population. Fig. 200. Close up of valve at pole showing form of distal raphe ending and shape of areolae. Scale bar in Fig. 189 = 10 μm for LM figs 178–189 and in Fig. 192 = 10 μm for LM figs 190–192. Scale bar in all SEM micrographs = 1 μm.