Encyonopsis alpina 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 : 103-105

Encyonopsis alpina Krammer & Lange-Bertalot ( Figs 73–98 and Figs 99–138 )

Description: Valves not or only slightly dorsiventral with weakly convex dorsal and weakly convex to straight ventral margin. Clear shoulders may be visible or absent. Length 11–20 μm; width 2.7–3.8 μm; maximum L:W ratio 5.9.Apices clearly protracted and capitate. Axial area narrow and central area only slightly differentiated dorsally. Striae weakly to clearly radiate, only occasionally with a somewhat shortened stria at valve centre. Striae uniform or occasionally appearing somewhat more coarsely spaced at valve centre ( Figs 73 & 95 ). Average stria density only slightly higher dorsally (32.5 in 10 μm) than ventrally (31 in 10 μm). Raphe filiform, curved to the dorsal side, terminating in inconspicuous pores proximally and having small round to oval shaped pores distally. Puncta small rounded to slightly peanut shaped. Irish populations are morphologically equivalent to the type population, with the most significant difference from the species diagnosis relating to a higher range in stria (max 35.5 in 10 μm) and areolae density reported here.

Ecology: Occurring in some alpine oligotrophic lakes with high oxygen concentration. E. alpina is a cosmopolitan taxon and occurs in well buffered, moderate to high alkalinity lakes (n=21) reaching a maximum relative abundance of 30%. A total phosphorus optimum close to 10 μg/l-P suggests a sensitivity score S=1 for lake ecological assessment ( Fig.532 ).

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.

FIGURES 73–98. Encyonopsis alpina Krammer & Lange-Bertalot Typus: Prap. 5b IOK. Individuals from type material Typus: Prap. 5b IOK. Figs 73–94. LM. Figs 73–94. Valves showing morphological variability and variation in size in type population. Figs 95–98. SEM. Fig. 95. External view. Fig. 96. External view of tilted frustule illustrating the arrangement of the intact cingulum, composed of two bands, with copulae tapered near the middle and having a single visible row of pores. Figs 98. Internal view. Scale bar in Fig. 94 = 10 μm for all LM figures. Scale bar in all SEM micrographs = 2 μm.

FIGURES 99–138. Encyonopsis alpina Krammer & Lange-Bertalot. Individuals from Ireland. Figs 99–131. LM. Figs 99–131. Valves showing morphological and variability in size for populations from Irish lakes. Figs 132–138. SEM. Figs 132–135. External view. Figs 136–138. Internal view. Scale bar in Fig. 131 = 10 μm for all LM figures. Scale bar in all SEM micrographs = 1 μm.