Planothidium galaicum Álvarez-Blanco & S. Blanco, 2013

Álvarez-Blanco, Irene & Blanco, Saúl, 2013, Planothidium galaicum sp. nov. (Bacillariophyta, Achnanthidiaceae), a new diatom species from Galician coast, Spain, Phytotaxa 151 (1), pp. 44-52 : 45-48

Planothidium galaicum Álvarez-Blanco & S. Blanco , sp. nov. ( Figs. 2–25 )

Type :— SPAIN. Muxía coast (43° 6' 47.64" N, 9° 13' 10.97" W). S. Blanco, 1-7-2011 (holotype LEB! 024) .

Frustula aspectu cinguli rectangularia modice transapicaliter deflexa. Valvae lanceolatae vel rhombico-lanceolatae apicibus protractis rotundatis obtusatis quoad specimina minora, 9.2−15.6 µm longae, 4.7−6.0 µm latae. Raphovalva: area axialis angusta linearis, area centralis modice expansis transapicaliter vel absentis. Raphe recta filiformis poribus centralis externe dilatatis triangularis, fissuris terminalis deflexis. Interne raphosternum leviter elevatum extremis centralibus raphis deflexis ad directiones oppositas, extremis ditalibus in helictoglossis inconspicuis terminantes. Striae transapicales 4−5 seriebus rotundarum parvarum areolarum per interne elevatas interstrias separatae, 14−18 in 10 µm. Striae fortiter radiatae, stria media abbreviata. Areolae non discernandae in microscopio photonico. Areovalva: sternum angustum lineare leviter depressum. Area centralis nulla. Striae transapicales multiseriatae parallelae in media parte sed radiatae ad apices, 16−20 in 10 µm. Striae interne per costas separate. Interstriae externe inconspicuae per series rotundis spinulis plerumque substitutae, spinulae maximae affinis margini valvae. Areolae non discernandae.

Frustules rectangular in girdle view, slightly bent about transapical axis. Valves lanceolate to rhombiclanceolate with protracted, rounded apices which tend to be blunt in small individuals, 9.2–15.6 µm in length, 4.7–6.0 µm in breadth (26 valves measured). Raphe valve ( RV, Figs. 8–12, 14–18 , 24, 25 ): axial area narrow, linear; central area slightly transapically expanded or lacking. Raphe straight, filiform, with external central pores enlarged, triangular in shape and deflected terminal fissures ( Fig. 25 ). Internally, the raphe-sternum is slightly elevated with the central raphe endings bent in opposite sides and the distal raphe endings terminate in a small helictoglossa ( Fig. 24 ). Transapical striae composed of 4–5 rows of small, rounded areolae, internally separated by raised interstriae ( Fig. 24 ), 14–18 in 10 µm. Striae strongly radiate, with one shorter striae on each side of the central region. Areolae not resolvable in LM. Rapheless valve ( RLV, Figs. 2–6, 20–23 ): central sternum narrow, linear, slightly depressed. Central area absent. Transapical striae multiseriate, parallel in midvalve and becoming more radiate towards the valve apices, 16–20 in 10 µm. Internally, striae separated by ribs ( Fig. 20 ). External interstriae inconspicuous or absent, in its place, rows of small and rounded spinules appear in most individuals, 20–30 in 10 µm ( Figs. 21–23 ). The largest spinules border the valve margin ( Figs. 21, 22 ). Areolae not resolvable in LM.

Etymology:—The epithet refers to the region where the sample was collected (Galicia).

Figures

FIGURES 2–22. Planothidium galaicum. Type population. Figs. 2–19. LM micrographs. Figs. 20–22. SEM micrographs. Figs. 2–6. Rapheless valves. Figs. 7, 13, 19. Girdle views of an entire frustule. Figs. 8–12, 14–18. Raphe valves. Fig. 20. Internal view of rapheless valve showing the raised sternum and the interstriae. Fig. 21. External view of a rapheless valve showing the spinules developed in the interstriae. Fig. 22. External detail of the apex of the rapheless valve showing the spinules, which are wider in the valve margin. Scale bar: 10 µm (Figs. 2–19), 2 µm (Figs. 20, 21), 1 µm (Fig. 22).

FIGURES 23–25. Planothidium galaicum. Type population. SEM micrographs. Fig. 23. External view of the rapheless valve. Fig. 24. Internal view of the raphe valve showing the raised sternum and interstriae. Fig. 25. External view of a raphe valve showing de enlarged central pores and the deflected terminal fissures. Scale bar: 2 µm (Figs. 23–25).