Encyonopsis carraensis 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 : 98-101

Encyonopsis carraensis Kennedy, Buckley & Allott sp. nov. ( Figs 3–27 )

Type:— IRELAND. Co. Mayo: Lough Carra , 53.69138267 N, 9.22379978 W, elev. 18.0 m, coll. B. Kennedy, coll. date 12 August 2014. (Holotype: specimen here designated Finder: Q42 (The England FinderTM Graticule) TCD0018335 , illustrated in Fig. 11 ; isotype, slide Zu11–19, Alfred Wegener Institute) .

LM ( Figs 3–18 ):—Cells solitary. Valves weakly lanceolate to linear-lanceolate and only weakly dorsiventral, with slightly convex margins, occasionally straightened ventrally. Apices are clearly protracted, subcapitate to capitate and rounded, with no indication of shoulders. Valve dimensions (n=51): length 17.2–22.6 μm, width 2.8–3.5 μm, valve L: W ratio 5.5–7.3. Sternum narrow, linear. Central area non-existent or hardly discernible due to only slightly shortened dorsal striae. Raphe filiform, slightly ventrally then dorsally curved with inconspicuous proximal and comma shaped distal raphe fissures. Striae lineate, uniseriate, weakly radiate and almost uniformly spaced throughout the valve length, occasionally slightly coarser and denser at valve centre and apices respectively, ranging from 26–30 dorsally and 25–29 ventrally in 10 μm. Areolae not discernible with LM.

SEM ( Figs 19–27 ):—Striae consist of 5–6 areolae, 40–50 in 10 μm ( Fig. 21 ). Very diverse shape and orientation of external areolae openings; predominately apically orientated and slit like, but transapical, rotated, comma, Y-shaped and X-shaped puncta were observed on the same valve and quite variable between populations. 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 fissures deflected ventrally over broadly rounded poles, ending in small pores externally ( Fig. 21 ). Internal striae with undulating margins. Raised silica struts between oval shaped apically orientated or rotated areolae. Proximal raphe endings not visible below a prominently raised central nodule. Distal raphe endings terminate as well developed helictoglossae.

Etymology:—The specific epithet carraensis refers to Lough Carra, Ireland’s largest marl lake where the species is abundant.

Similar species:—The morphological characteristics including high L:W ratio, linear valve outline, distinctly protracted apices and striae density enable differentiation from similar taxa using LM alone ( Figs 3–20 ). Larger valves of E. carraensis are comparable to the narrowest valves of E. neerlandica . When both co-occur, the more broadly lanceolate outline and rostrate ends of the latter enables their clear separation. The proximal raphe ends internally are not visible in E. carraensis and differing shape of external areolae openings are also discriminating ultrastructural characteristics. The lower L:W ratio, broader lanceolate outline and more obviously capitate apices typically allows for all common Encyonopsis taxa in the study.

a clear separation of E. subminuta . There was difficulty differentiating isolated valves of some less clearly protracted and narrow frustules of E. subminuta in LM, but this form was very rare. Ultrastructurally, both taxa differed in puncta shape. Valve length of E. carraensis has a similar range to E. krammeri , but a combination of moderate dorsi-ventral outline and more distinctly arched dorsal margin enables a clear differentiation. Some populations of E. krammeri with distinctly capitate poles can be distinguished by clear dorsiventral outline and higher stria density. Puncta shape, orientation and form of the distal raphe fissures also differ significantly in SEM. The L:W ratio and outline of E. krammerioides Lange-Bertalot & Rumrich in Rumrich et al. (2000: 117) are comparable, but narrower width, higher stria density and clearly protracted ends of E. carraensis are differentiating. Conspecificity with E. anaconda Bahls (2013) can also be ruled out based on rostrate ends and broader lanceolate valve outline equivalent to E. neerlandica of this taxon, but type material is unavailable for comparison of ultrastructural differences (L. Bahls pers comm.).

Distribution & Ecology:— Encyonopsis carraensis was found in 12 lakes reaching a maximum relative abundance of 39% in lower Lough Corrib, Co. Galway. It occurs in oligotrophic calcareous lakes ( Fig. 28 ) where the upper littoral is dominated by a marl precipitating community of Schizothrix Kützing ex M. Gomont (1892: 2002) and Dichothrix G.Zanardini ex É.Bornet & C.Flahault (1886: 373) .

Figures

FIGURE 28. Lough Carra, Co. Mayo. Shoreline at Pleasure Island (a) the type locality of Encyonopsis carraensis with an extensive deposit of submerged (b) and exposed (c) marl precipitating cyanobacteria over boulders.

FIGURES 3–27. Encyonopsis carraensis sp. nov. Figs 3–20. LM. Fig. 11. Holotype specimen. Figs 3–20. Valves showing morphological range and size variation in populations. Figs 21–27. SEM. Fig. 21. External view. Figs 22–23. Internal view. Figs 24–27. Variation in valve outline. Scale bar in Fig. 20 = 10 μm for all LM figures. Scale bar in all SEM micrographs = 1 μm.