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).