Encyonopsis neerlandica Van de Vijver, Verweij, Van der Wal & Mertens

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 : 118-119

Encyonopsis neerlandica Van de Vijver, Verweij, Van der Wal & Mertens ( Figs 481–510 )

Description: Characterised by relatively large valves for a diatom in the microcephala -complex, lanceolate to broadly lanceolate in outline with convex margins and rostrate to subcapitate apices. Length 13.6–31.6 μm; width 3.0– 4.5 μm; maximum L:W ratio 8.3. Mostly comparable to the type description but populations in Irish lakes also have distinctly capitate rounded apices ( Figs 492–494, 505, 509 ). Larger valves and initial cells may have non-protracted narrowly rounded ends. Striae are parallel or weakly radiate at centre, becoming increasingly radiate towards the poles. Stria density 25–30 dorsally and 24–29 ventrally in 10 μm. Stria density in Irish populations exceed that reported for type material and valves have a higher maximum L:W ratio. Axial area narrow and central area absent, rarely with a single slightly shortened stria at valve centre. Ultrastructural characters are equivalent to that given with the original species description.

Ecology: E. neerlandica is widespread in peatland catchments in the West of Ireland, occurring in 26 lakes and reaching a maximum relative abundance of 54%. Its ecology is equivalent to that reported by Van de Vijver et al. (2012) and is found in low to moderate alkalinity, near-neutral humic lakes. It is also found in a number of samples from Cronaniv Burn (max. 9.5%), a river in a near-pristine peatland catchment overlying siliceous geology in Co. Donegal and less frequently in the Bundorragha River, a lake outflow in Co. Mayo. Although found in near-pristine reference lakes, it has a maximum abundance at mesotrophic condition, suggesting a sensitivity value of S=2 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 481–510. Encyonopsis neerlandica Van de Vijver, Verweij, Van der Wal & Mertens. Figs 481–501. LM. Figs 481–501. Valves showing morphological range and size reduction series in populations from Irish lakes. Figs 502–510.SEM.Figs 502 & 504–506. External view showing variation in size and shape of apices. Figs 507–510. Internal view. Figs 507–509. Variation in valve outline and shape of apices. Fig. 510. Detail of valve apex and helictoglossa. Scale bar in Fig. 490 = 10 μm for LM figures 481–490. Scale bar in Fig. 501 = 10 μm for LM figures 491–501. Scale bar in all SEM micrographs = 1 μm.