Cavinula pusio (Cleve) Lange-Bertalot

Cvetkoska, Aleksandra, Levkov, Zlatko, Hamilton, Paul B. & Potapova, Marina, 2014, The biogeographic distribution of Cavinula (Bacillariophyceae) in North America with the descriptions of two new species, Phytotaxa 184 (4), pp. 181-207 : 195-196

Cavinula pusio (Cleve) Lange-Bertalot ( Figs 127–131 )

Basionym: Navicula pusio Cleve 1895, p. 9 , fig. 2: 3

Valves elliptical to linear-elliptical with broad rostrate apices. Valve face flat, curving into a shallow mantle. Valve length 19–23 µm, width 8.5–11 µm. Axial area narrow and linear, central area slightly apically expanded. Striae strongly radiate throughout. Striae around central area alternating long and short. Stria density 30–36 in 10 µm. Internally, axial area with slightly thickened lanceolate ridge; raphe linear distal fissures end with helictoglossa and proximal fissures terminate as small pores. Externally raphe positioned on a narrow ridge with depressions along each side. Proximal fissures indistinct positioned within tear-drop pores, distal fissures deflected in opposite direction and terminate on valve face. Isolated areolae maybe present in hyaline region at apex. Externally areolae round to elliptical, foramina a shallow depression. Areolae along axial area larger, with linear slit-like areolae around mid-valve and central area. Internally, areolae rows positioned between costae and each areola occluded with a hymen.

Type:— Rotorua Lake , New Zealand, lectotype slide S mic-7383, lectotype designated here, S mic-7383, lectotype specimen = Fig. 128 .

Observations:— C. pusio was observed from a slide (mic-7383) in the Cleve collection at the Stockholm Museum of Natural History (S) ( Fig. 128 , lectotype, plus 3 additional specimens) and material ( RP 6-7 ) collected from Lake Rotorua by Berggren (only one specimen). We were not able to document this taxon in SEM from material samples collected by Berggren or from recent samples collected from Lake Rotorua ( CANA 93697–93700 , 93711–73713 ) across five microhabitats. Recent anthropogenic impacts have changed the water conditions of Lake Rotorua which could explain why we did not observed any Cavinula in recent collections .

Cavinula pusio is identified by the linear-elliptic to elliptic valve with broadly rostrate apices and fine radiate striae that alternate long and short around the central area. The closest taxon to compare within the genus Cavinula would be Cavinula lacustris (Gregory) Mann & Stickle (1990, p. 665) , here as ( Figs 99, 100 ) from type slide (Greville 596), but the two taxa can be distinguished by valve outline ( C. pusio is more linear with broad rostrate apices while C. lacustris has narrower, more cuneate valve apices), stria density (24–27 in 10 µm in C. lacustris compared to 30–36 in 10 µm striae density in C. pusio ) and the shape and size of the central area (narrow, linear in C. pusio and roundedelliptic in C. lacustris ). In SEM (external view), the raphe of C. pusio is positioned on a small ridge, the proximal raphe pores have a thickened rim, areolae around the central area are elongated, and isolated pores are present on the valve face and mantle at the apex (http://westerndiatoms.colorado.edu/taxa/species/cavinula_pusio).

Cavinula cocconeiformis is separated by valve shape, areolae size, and orientation. Both C. pusio and C. cocconeiformis have the same “s-shaped” raphe with distally deflected fissures in opposite directions, while another related taxon C. vincentii has isolated slit-like pores adjacent to the raphe distally which mimic the s-shaped raphe. Navicula detenta Hustedt (1943: 164) is similar in outline to C. pusio , but distinguished by a finer raphe, lower stria density, absence of a central area and even stria (not alternating long and short) around the central region of the valve.

Distribution:— This taxon has been reported from Europe, Svalbad and North America. C. pusio has confirmed identifications from the Northwestern United States ( Bahls 2013) and in Canada from the Arctic Archipelago (Baffin Island) and Lac des Ours (Southern Québec). Reports of C. pusio from the southern United States could not be verified after examination of slides from the ANSP collection. This is a rare species which has a relatively broad distribution across northern North America.

Distribution Records:— Cleve (1895, line drawing, type drawing, 9, fig. 2: 3, New Zealand), Werum & Lange- Bertalot (2004, fig. 130, fig. 31: 18, 19, Europe), Foged (1974, fig. 79, fig. 17: 5, Iceland), Bahls (2012, SEM http:// westerndiatoms.colorado.edu/taxa/species/cavinula_pusio, USA).

Figures

FIGURES 101–131. LM micrographs. Figs 101–106. Cavinula scutelloides (W. Smith) Lange-Bertalot. Figs 107–111. Cavinula scutiformis (Grunow ex A. Schmidt) Mann & Stickle. Figs 112–122. Cavinula hilliardii Manguin ex Kociolek & Reviers. Figs 123,124. Cavinula variostriata (Krasske) Mann in Round, Crawford & Mann. Figs 125, 126. Cavinula lapidosa (Krasske) Mann. Figs 127–131. Cavinula pusio (Cleve) H. Lange-Bertalot in Werum & Lange-Bertalot. Figs 103, 104. W. Smith, Omersby, 1853 (type slide). Figs 126, 128. BRM N14/87a (Krasske material near Hessen). Scale bar: 10 µm.

FIGURES 44–100. LM micrographs. Figs 44–73. Cavinula pseudoscutiformis (Hustedt) Mann & Stickle. Figs 64–73. Cavinula pseudoscutiformis (Morphotype 3). Figs 74–81. Cavinula vincentii Antoniades & Hamilton. Figs 82–92. Cavinula jaernefeltii (Hustedt) Mann & Stickle. Fig. 84. BRM N12/84 (lectotype slide). Figs 93–98. Cavinula davisiae Bahls, ANSP GC65165 (isotype slide). Figs 99, 100. Cavinula lacustris (Gregory) Mann & Stickle, BM 596 (holotype slide). Scale bar: 10 µm.