Surirella parahelvetica Cvetkoska, Levkov & Hamilton, 2014

Surirella parahelvetica Cvetkoska, Levkov & Hamilton sp. nov. ( Figs 20–42 View FIGURES 20–37 View FIGURES 38–42 )

Valves isopolar about apical axis, lanceolate to rhombic–lanceolate with acute apices ( Figs 20–37 View FIGURES 20–37 ). Valve length 24–50 µm, width 10–20 µm. Valve face undulated in apical direction; undulations from valve margin to median area. Externally, each undulation aligned with an alar canal and depressions in between connected to fenestrae ( Fig. 38 View FIGURES 38–42 ). Alar canals broad, with almost equal width as fenestrae ( Figs 38, 40 View FIGURES 38–42 ), 20–30/ 100 µm. Surface undulations parallel to somewhat radial, covered with irregularly arranged short tube-spines ( Fig. 38 View FIGURES 38–42 ). Striae finely punctate, 36–42/ 10 µm. Externally, striae extend onto alar canals and fenestrae ( Fig. 41 View FIGURES 38–42 ), internally on entire valve and also continue to space between alar canals ( Figs 39, 40 View FIGURES 38–42 ). Puncta externally open as simple rounded pores, internally puncta rimmed ( Figs 41, 42 View FIGURES 38–42 ). Median area narrow, elevated as a narrow silica ridge, terminating before valve apices ( Figs 38–41 View FIGURES 38–42 ). Wing projection vertical, separated from valve face ( Fig. View FIGURES 38–42 38). Marginal keel developed, with grooves extending along both sides of raphe ( Figs 38, 41 View FIGURES 38–42 ). Spines conic (black arrow on Fig. 38 View FIGURES 38–42 ) and tube-like (white arrow on Fig. 38 View FIGURES 38–42 ) scattered across external valve face and alar canals (black arrow on Fig. View FIGURES 38–42 41). Row of short thick nodules along inner side of keel (white arrow in Fig. 41 View FIGURES 38–42 ). Internally, terminal raphe fissures simple, not deflected ( Fig. 42 View FIGURES 38–42 ). Fenestrae rectangular, occluded with 3–4 fenestral bars. Alar canals cylindrical in shape; 20–30 in 100 µm, internally openings appear as simple elliptical portulae ( Figs 39, 40 View FIGURES 38–42 ).

Type:— MACEDONIA: Lake Prespa, sediment, core Co1215, core depth 265 cm, ca. 14.5 cal ka BP , collection date: October 2009 (holotype! slide MKNDC 005421/A , designated here, Accession No. MKNDC 005421; holotype specimen = Fig. View FIGURES 20–37 28 ; isotypes BRM ZU9/35 , CANA 93610 ).

Observations: — Surirella parahelvetica resembles S. helvetica Brun (1880: 100 , figs 2: 4; 9: 28) with respect to the valve size (L= 40–70 µm; W= 13–18 µm) and presence of spines scattered on the valve face. However, S. parahelvetica can be distinguished from S. helvetica by the elliptic rhombic valve outline compared to the linear to linear-elliptical valve outline with rounded apices of S. helvetica sensu stricto. Several authors, Migula (1907: fig. 15E: 10), Hustedt (1912: in Schmidt et al. fig. 282: 7–9) and Meister (1912: 223, fig. XLI: 6) were the first to illustrate S. helevtica ( S. linearis var. helvetica ) as linear-elliptic to elliptic-lanceolate valves with narrowly rounded acute apices and deeply recessed fenestrae. Cleve-Euler (1952: 107, fig. 1531 a-d) further followed the elliptic-lanceolate valve outline for S. helvetica . Güttinger (1991: fig. 2.09.05-7, as S. helvetica ) presented SEM images of this valve having elliptic-rhombic to elliptic-lanceolate valves with deeply recessed fenestrae and tubespines. The elliptic-rhombic to elliptic-lanceolate valves presented by Güttinger probably belong to S. parahelvetica . Surirella amoena Pantocsek (1892 , fig. 18: 268) has valves with an elliptic-lanceolate outline and larger valve width (B=25.5 µm). According to Krammer & Lange-Bertalot (1988: 196) S. amoena is possibly a small form of S. bifrons . Surirella parahelvetica can be separated from Surirella roba ( Leclercq 1983: 495, figs 1: 2–6, 2: 2–8, 3:1–6) by valve outline, elliptic rhombic to elliptic lanceolate in S. parahelvetica and linear-lanceolate in S. roba , valve width (W= 8–11 µm in S. roba ), the number of alar canals (36–50/ 100 µm in S. roba ) and the absence of spines. S. parahelvetica currently has a European distribution and may lightly be more globally distributed.