Encyonopsis angusta Krammer & Lange-Bertalot, 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 : 106

Encyonopsis angusta Krammer & Lange-Bertalot ( Figs 139–151 )

Description: In the diagnosis valves were described as weakly dorsiventral, linear to linear elliptical in outline with very weakly convex dorsal and ventral sides. Poles relatively broadly rounded capitate, with clear shoulders.Axial area is narrow and central area absent. Length 13–25 μm; width 3.4–3.6 μm; maximum L:W ratio 4.5, but when remeasured from original plates was determined to be ≥5.0. The combination of characters enabling identification were proposed as; outline with distinct shoulders, relatively broad capitate ends, very elongate, having approximately 33 delicate transapical striae in 10 μm.

Several Encyonopsis taxa are present on the type slide and valves illustrated in Figs 139–151 most closely follow the illustrations of E. angusta provided by Krammer (1997b). The selected valves have a lower minimum valve width (2.9 μm) and greater maximum L:W ratio (6.2) but are otherwise comparable to the diagnosis. Another diatom more with an affinity to E. krammeri is well represented on the slide ( Figs 152–173 ). These valves are clearly dorsiventral and have slightly less protracted, narrower rostrate to subcapitate poles. However, they probably represent a continuation of the same diatom described above (see plates of E. krammeri below and discussion). E. alpina ( Figs 174–177 ) was also found on the slide, while E. subminuta and E. minuta are less frequent and are not illustrated.

Ecology: Reported to be frequent in suitable oligotrophic alpine and pre-alpine lake habitats in waters with high oxygen concentration. Not found with certainty in Ireland, although valves with a similar morphology are occasionally encountered but are considered to represent a capitate form of E. krammeri .

Figures

FIGURES 139–177. Encyonopsis Typus: Prap. 77A IOK. Figs 139–177. LM. Figs 139–151. E. angusta Krammer & Lange-Bertalot. Figs 152–173. Encyonopsis krammeri Reichardt. Figs 174–177. E. alpina Krammer & Lange-Bertalot. Scale bar in Fig. 151 = 10 μm for all LM figures.