Thalassionema cf. bacillare HK

Sabir, J. S. M., Theriot, E. C., Lobban, C. S., Alhebshi, A. M., Al-Malki, A. L., Hajrah, N. H., Khiyami, M. A., Obaid, A. Y., Jansen, R. K. & Ashworth, M. A., 2018, Systematics of araphid diatoms with asymmetric rimoportulae or densely packed virgae, with particular attention to Hyalosynedra (Ulnariaceae, Bacillariophyta), Phytotaxa 347 (1), pp. 1-49 : 27

Thalassionema cf. bacillare HK 361 ( Figs 69–72 )

Synonym: — Thalassionema sp. BlueH20 HK 361 in Edward C. Theriot, Nakov et al. (2014), Lobban and Ashworth (2014a,b), Theriot et al. (2015).

Material studied: — Wild and cultured ( HK 361) material isolated from the same collection: ECT3929 , collected by plankton net from the Gulf of Mexico , Texas, USA (27° 38.06’ N; 96° 42.21’ W) .

Description and remarks: —We observed valve lengths of 382.5–402.9 μm and widths of 3.2–4.0 μm, with 9–10 areolae per 10 μm. Areolar bars were incomplete, with some branching. Girdle bands were open and without pores. Rimoportulae were observed at each pole, and were subterminal, with symmetric sides that were arranged parallel to the transapical axis.

Remarks: —This diatom did not fit well the keys or descriptions of any Thalassionema species ( Hasle & de Mendiola 1967, Hallegraeff 1986, Hasle 1999, Hasle 2001, Sar et al. 2007, Sugie & Suzuki 2015). Its size suggested possible affinities to T. bacillare or T. synedriformis , the two largest described Thalassionema species. However, it lacked several features of T. synedriformis , including shape, the ridge at the valve face-mantle junction at the footpole and the elaborate covering over the areolae. It was also slightly more coarsely areolate than reported for T. synedriformis ( Sugie & Suzuki 2015) . It was most similar to T. bacillare in areolar density and construction. Although the areolar bar was incomplete on all specimens observed, almost all showed evidence of branching, resembling the Y-shaped covering of T. bacillare . However, our specimens had distinctly subterminal rimoportulae, located well up on the valve face, while those illustrated for T. bacillare (and T. synedriformis ) are terminal, near or at the junction of the face and mantle. DNA sequences from this strain were previously reported as belonging to Thalassionema sp. HK 361/ECT3929ThalBlue in Lobban and Ashworth (2014a,b).

Figures

FIGURES 69–72. Thalassionema cf. bacillare from culture HK361. 69. Whole valve. 70. Detail of apex, exterior view. 71. Detail of exterior of central area, where some areolae had a T- or Y-shaped bar. 72. Detail of internal area of apex showing subterminal rimoportula with slit aligned along apical axis.