Haslea staurosigmoidea Sterrenburg & Tiffany, 2015

Sterrenburg, Frithjof A. S., Tiffany, Mary Ann, Hinz, Friedel, Herwig, Wulf E. & Hargraves, Paul E., 2015, Seven new species expand the morphological spectrum of Haslea. A comparison with Gyrosigma and Pleurosigma (Bacillariophyta), Phytotaxa 207 (2), pp. 143-162 : 146-148

Haslea staurosigmoidea Sterrenburg & Tiffany , sp. nov. ( Figs 10, 11 : LM, 21–26: SEM)

Type:—” Itacorubi, Florianopolis, Brasil, August, 21, 1987, leg. de Souza Mosimann”, geographic coordinates 27°34’ S, 48°29’ W. Holotype BRM ZU9/87, slide coordinates 15.0 E, 18.1 S. Isotypes in collection Sterrenburg #596.

FIGURES 12, 13. H . feriarum sp. nov. Fig. 12 . Holotype. Fig. 13 . Isotype.

FIGURES 14, 15. H .tsukamotoi sp. nov. Fig. 14 . Holotype. Fig. 15 . Isotype.

FIGURES 16, 17. H . meteorou sp. nov. Fig. 16 . Holotype. Fig. 17 . Isotype.

FIGURE 18. H . clevei sp. nov., holotype, complete frustule.

FIGURES 19, 20. H . avium sp. nov. Fig. 19 . Holotype, inset: arrow marks continuous fissures. Fig. 20 . Isotype.

Valve ( Figs 10, 11 , 21, 22 ) delicate, sigmoid with a narrow pseudostauros, 100–120μm long, 6.5–7.5 μm wide, almost parallel-sided in the middle portion, with acute apices. Raphe sternum central over most of the valve length but becoming eccentric near the apices, curved. Raphe angle circa 7°. Striae perpendicular, transverse circa 30 in 10 μm, longitudinal circa 40 in 10 μm. In LM, axial and central area so narrow that there is no clear hyaline space separating striae and raphe sternum, central raphe node minute. In SEM, the tegumental layer shows little surface relief ( Figs 23, 25, 26 ) and broad marginal zones not perforated by longitudinal fissures. External central raphe endings very approximate and slightly curved either to the same side ( Fig. 25 ) or oppositely ( Fig. 26 ); apical raphe endings more or less straight; ( Fig. 23 ); small apical fissure present (arrow in Fig. 23 ). Internally, transverse silica ridges (pseudostauros) are present on both sides of the very narrow central raphe node, extending over the full width of the valve, only about 1 interstria wide; the pseudostauros is joined to a longitudinal ridge along the raphe on one side and a long central bar on the other ( Fig. 24 ). Helictoglossa prominent ( Fig. 22 ). Basal layer: transverse bars of the perpendicular grate slightly broader than the longitudinal, foramina more or less square in the central portion ( Fig. 24 ), apically elongated oblong near the apices ( Fig. 22 ).

Etymology:— The specific epithet refers to the sigmoid valve contour and pseudostauros.

Habitat:— Muddy marine-littoral sediment.

Distribution:— Brazil, marine littoral, not rare in the sample. One of us (WEH) has observed diatoms matching H. staurosigmoidea (in LM!) in the Adriatic Sea.

Observations:— The species resembles a Gyrosigma in LM because of its sigmoid contour but the pseudostauros, minute central raphe node (in contrast to the evident round to oval node usual in Gyrosigma ) and inconspicuous axial and central areas indicated that SEM investigation was necessary, which revealed the Haslea - type valve structure. A particularly noteworthy finding is the variability of the central raphe ending deflection, which in the same population was either to the same, or to opposite sides. Saepes not satisfactorily visualized, no fragmented valves found.

In LM, this species is readily separated from H. nipkowii by the presence of the pseudostauros, in SEM there are additional major differences, e.g. in the shape of the apical and central external raphe fissures. The sigmoid species H. sigma Talgatti, Sar & Torgan ( Talgatti et al. 2014) also has a pseudostauros like H. staurosigmoidea . The characters separating these two species are given in Table 1.

Figures

FIGURES 10–20. New Haslea species, LM images (DIC).All bars = 10 μm. All except Fig. 11 are stacks of 12–22 separate images. FIGURES 10, 11. H. staurosigmoidea sp. nov. Fig. 10. Holotype, Fig. 11. Isotype, aspect in normal DIC corresponding to what is seen on visual inspection.

FIGURES 21–26. H. staurosigmoidea sp. nov. SEM, isotypes. Fig. 21. General aspect, bar = 5 μm. Fig. 22. Apex, exterior, bar = 2 μm. Fig. 23. Apex, interior, bar = 2 μm.Arrow marks apical pore. Fig. 24. Centre, interior showing pseudostauros, bar = 2 μm. Fig. 25. Centre, exterior, raphe endings deflected to the same side, bar = 1 μm. Fig. 26. Centre, exterior, raphe endings oppositely deflected, bar = 1 μm.