Encyonopsis hibernica Kennedy, Buckley & Allott, 2019

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 : 101-103

Encyonopsis hibernica Kennedy, Buckley & Allott sp. nov. ( Figs 29–71 )

Type:— IRELAND. Co. Clare: Lough Inchicronan , 52.92222687N, 8.9026442W, elev. 26.0 m, coll. Dr. Ruth Little, coll. date 16 April 2012. (Holotype: specimen here designated Finder: N47 (The England FinderTM Graticule) TCD0018336 , illustrated in Fig. 44 ; isotype, slide Zu11–20, Alfred Wegener Institute) .

LM ( Figs 29–60 ):—Cells solitary. Valves lanceolate and weakly dorsiventral, with convex margins and without clear shoulders. Apices clearly protracted, with broadly rounded subcapitate poles. Valve dimensions (n=45): length 10.1– 13.0 μm, width 2.6–3.5 μm, valve L: W ratio 3.3–4.4. Sternum narrow, linear. Central area small to hardly discernible due to only slightly shortened dorsal or ventral striae. Raphe filiform, ventrally then dorsally curved with inconspicuous proximal and strongly deflected distal raphe fissures. Striae lineate, uniseriate, weakly radiate throughout the valve length or sometimes parallel, more commonly with shortened, radiate or deflected stria at central area, ranging from 28–31 dorsally and 26–31 ventrally in 10 μm. Areolae not discernible with LM.

SEM ( Figs 61–71 ):—Stria consist of 5–7 areolae, 46–60 in 10 μm ( Fig. 61 ). External and internal areolae openings are round, oval or slightly peanut shaped. Raphe slightly curved to the ventral side, shifting towards dorsal side at valve middle, with slightly enlarged central endings and inconspicuous central pores. Distal raphe endings strongly deflected ventrally over broadly rounded poles, terminating in expanded fissures externally ( Fig. 61 ). Internal striae with straightened margins. Proximal raphe endings not visible below a prominently raised central nodule. Distal raphe endings terminate as well developed helictoglossae.

Etymology:—The specific epithet hibernica refers to Ireland where the species is found.

Similar species:—The morphological characteristics including valve dimension, broadly rounded subcapitate apices and stria orientation at the central area allow differentiation from similar taxa using LM alone ( Figs 29–60 ). E. hibernica has a comparable outline to less clearly protracted, smaller valves of E. minuta . Although stria density overlap, the latter typically has coarser parallel stria, only occasionally having a single shortened or offset stria at the central area. Absence of an intermissio, differing shaped terminal fissures and puncta are also discriminating ultrastructural characteristics. The valve dimensions and striation pattern at the central area of E. hibernica are often comparable to E. horticola . However, valve apices in the latter are rostrate to subrostrate and never capitate to subcapitate. Striae may be weakly radiate to sub-parallel near the central area in E. hibernica but always have a clear change in direction in E. horticola . The shape of their terminal raphe fissure also differs. The linear-lanceolate outline and lower stria density of E. bobmarshallensis are clearly differentiating, while E. perborealis Krammer (1997: 109) also has a more linear outline, stria density in the lower range of E. hibernica , less distinctly or non-protracted poles, weakly radiate striae and different shaped puncta.

Distribution & Ecology:— Encyonopsis hibernica is found in samples from 19 lakes reaching a maximum relative abundance of 26% in Lough Inchicronan, Co. Clare. It favours mesotrophic lakes with elevated nutrients and substrate at the type location has macroscopic colonies of Chaetophora F. Schrank (1783: 19) with lesser Dichothrix G.Zanardini ex É.Bornet & C.Flahault with low levels of calcification.

Figures

FIGURES 29–71. Encyonopsis hibernica sp.nov.Figs 29–60.LM.Fig.44.Holotype specimen.Figs 29–60.Valves showing morphological range and size variation in several populations. Figs 61–71. SEM. Fig. 61. External view. Fig. 62. Internal view. Figs 63–71. Variation in valve outline. Scale bar in Fig. 60 = 10 μm for all LM figures except holotype specimen. Scale bar in all SEM micrographs = 1 μm and = 2 μm in Figs 65–70.