Rhoicosphenia californica E.W. Thomas & Kociolek, 2015

Thomas, Evan W. & Kociolek, J. Patrick, 2015, Taxonomy of three new Rhoicosphenia (Bacillariophyta) species from California, USA, Phytotaxa 204 (1), pp. 1-21 : 11-13

Rhoicosphenia californica E.W. Thomas & Kociolek , sp. nov. ( Figs. 75–110 )

Frustules clavate and strongly flexed in girdle view. Valves heteropolar in valve view, linear-lanceolate with protracted apices in larger specimens and rounded apices in smaller specimens, 8–50 μm long, 3–6 μm wide. Frustules heterovalvate, one valve concave with long raphe branches (R-valve), one valve convex with shortened raphe branches (D-valve). R-valve: raphe filiform, proximal raphe ends dilated externally, crook-shaped internally in same direction, distal raphe ends curved in same direction externally ending in helictoglossae internally. Axial area narrow, widening at small ovate central area. Striae parallel to radiate in center of the valve and radiate at apices, 11–12 striae in 10 μm at center of valve, 13–15 striae in 10 μm at apices, composed of round to lineolate areolae, 40 in 10 μm. D-valve: raphe branches 3–5 μm long at head pole, not extending beyond pseudoseptum, and 5–7 μm long at foot pole, external proximal ends not expanded, internal proximal ends crook-shaped in same direction and distal ends not inflated externally, terminate in helictoglossae internally. Striae parallel throughout, 12–14 striae in 10 μm at center of valve, 13–16 striae in 10 μm at apices, composed of round to lineolate areolae. Both valves with pseudosepta at each apex, 3–8 μm long. Both valves with apical pore field at foot pole, porelli 4 per 1 μm. Girdle bands open. In the SEM, an external view of the R-valve shows rounded puncta near the axial area and lineate puncta towards the margins ( Figs. 98, 100 ). At the head pole, the raphe continues onto the mantle and an open girdle band is visible ( Fig. 99 ). The central area has inflated proximal raphe ends ( Figs. 98, 100 ), and the foot pole has an apical pore field of rounded porelli ( Fig. 101 ). Internal views show the areolae through troughs between the virgae ( Figs. 102–104 ) and the proximal raphe ends are strongly crook-shaped in the same direction ( Figs. 103–104 ). The valvocopula in modified to overlap the pseudosepta and an aperture is present in the valvocopula at the head pole ( Figs. 102, 104 ), but not at the foot pole ( Fig. 104 ). External views of the D-valve show the shortened raphe branches and round to lineolate areolae ( Fig. 105 ). The distal raphe end at the head pole terminates on the valve face ( Fig. 106 ) and continues onto the mantle at the foot pole ( Fig. 107 ). The proximal raphe end at the head pole is small ( Fig. 106 ) are at the foot pole is dilated ( Fig. 107 ). In girdle view, the foot pole can be seen on each valve along with a single row of simple poroids on the valvocopula ( Fig. 108 ). Internal views show the external areolae through troughs between the virgae ( Fig. 109 ). Pseudosepta are covered at each pole by the valvocopula and the raphe branches extend beyond the pseudosepta at each pole ( Fig. 109 ). The proximal raphe end at the foot pole is crook-shaped and a small aperture in the valvocopula is evident ( Fig. 109 ). In girdle view, the valvocopula are ornamented with a single row of simple poroids ( Fig. 110 ).

Type:— USA. California: Big Chico Creek, Butte County, 39.72855º N, 121.88105º W, SWAMP Field Crew , June 30, 2008 (holotype ANSP! Circled specimen on slide GC XXXXX made from ANSP GCM XXXXX, illustrated in Fig. 84 ; isotype JPK! 3046, slide and material, University of Colorado, Museum of Natural History , Kociolek Collection , Boulder , Colorado, USA) .

Etymology:— Named for the state of California, where it commonly occurs.

Taxonomic remarks:— Rhoicosphenia californica is the species most different from the other species described in this paper and is also distinct from all other previously described taxa. The long, narrow valves distinguish R. californica from other species in California, but outside of the state, several other Rhoicosphenia have a similar valve shape. Rhoicosphenia tenuis Levkov & Nakov (2008: 379) is similar in length, but R. californica is wider (up to 6 μm) versus 5 μm in R. tenuis , and has less dense striae. Further, R. tenuis has very linear sides while R. californica is linear-lanceolate. Rhoicosphenia tenuis lacks an aperture in its valvocopula ( Levkov et al. 2010, fig. 14e), while R. californica has an aperture in its valvocopula ( Figs. 102 , 109 ). Rhoicosphenia californica also resembles R. baicalensis Skabichevskii (1976: 269) ( Levkov et al. 2010, figs. 15a–y), but the shape of R. californica is more angular and less linear than R. baicalensis and has denser striae at 11–12 in 10 μm versus 9–12 in 10 μm. Finally, R. californica is linear-lanceolate and distinct from the narrowly lanceolate Rhoicosphenia patrickae . R. californica is wider at 6 μm versus 4.5 μm wide for R. patrickae , and has slightly denser striae, 11–12 in 10 μm versus 10–11 in 10 μm. In addition, R. patrickae does not have an aperture in the valvocopula ( Thomas et al. 2015, fig. 83) while R. californica does possess an aperture.

The linear-lanceolate valves with protracted apices of R. californica distinguish this species from R. abbreviata , which is linear to narrowly clavate, but does not have protracted apices ( Levkov et al. 2010, Figs. 1a–v ). The striae of R. abbreviata are lineate on both valves ( Levkov et al. 2010, Figs. 2b, 2c, 2e, 2f, 3a–c ), while the striae of R. californica are lineate, but the striae bordering the axial area are often rounded ( Figs. 98–101 , 105–107 ).

Distribution and ecological notes:— Rhoicosphenia californica is the most commonly and widely distributed Rhoicosphenia in the state of California. Found in streams from sea level to approximately 2700 meters across a wide range of freshwater conductivities and nutrient levels.

Figures

FIGURES 75–97. Type material of Rhoicosphenia californica from Big Chico Creek, Butte County, California, USA. LM. 84. Holotype specimen. 76, 78, 81, 84–86, 88–90, 92, 94, 96. R-valves. 77, 80, 82, 83, 87, 91, 93, 97. D-valves. 75, 95. Girdle views. 79. Valvocopula. Scale bar is 10 μm.

FIGURES 98–104. Type material of Rhoicosphenia californica from Big Chico Creek, Butte County, California, USA. SEM. 98–101. External views of the R-valve show rounded puncta near the axial area and lineate puncta towards the margins (98, 100).At the head pole, the raphe continues onto the mantle and an open girdle band is visible (99). The central area has inflated proximal raphe ends (98, 100), and the foot pole has an apical pore field of rounded porelli (101). Internal views show the areolae through troughs between the virgae (102–104) and the proximal raphe ends are strongly crook-shaped in the same direction (103, 104). The valvocopula in modified to overlap the pseudosepta and an aperture is present in the valvocopula at the head pole (102, 104), but not at the foot pole (104). Scale bars are 5 μm (98) and 1 μm (99–104).

FIGURES 105–110. Type material of Rhoicosphenia californica from Big Chico Creek, Butte County, California, USA. SEM. 105–108. External views of the D-valve show the shortened raphe branches and round to lineolate areolae (105). The distal raphe end at the head pole terminates on the valve face (106) and continues onto the mantle at the foot pole (107). The proximal raphe end at the head pole is small (106) and at the foot pole is dilated (107). In girdle view, the foot pole can be seen on each valve along with a single row of simple poroids on the valvocopula (108). Internal views show the external areolae through troughs between the virgae (109). Pseudosepta are covered at each pole by the valvocopula and the raphe branches extend beyond the pseudosepta at each pole (109). The proximal raphe end at the foot pole is crook-shaped and a small aperture in the valvocopula is evident (109). In girdle view, the valvocopula are ornamented with a single row of simple poroids (110). Scale bars are 2 μm (105, 110), 1 μm (106–109).

FIGURES 1–22. Type material of Rhoicosphenia stoermeri from Bear Creek, Los Angeles County, California, USA. LM. 10. Holotype specimen. 1, 2, 4, 6, 7, 10, 12, 14, 15, 18, 20, 22. R-valves. 3, 5, 9, 11, 13, 16, 19, 21. D-valves. 8, 17. Girdle views. Scale bar is 10 μm.