orientale Takano emend. E. A. Sar & I. Sunesen

Sar, Eugenia A. & Sunesen, Inés, 2014, The epizoic marine diatom Sceptronema orientale (Licmophoraceae, Licmophorales): epitypification and emendation of specific and generic descriptions, Phytotaxa 177 (5), pp. 269-279 : 271-272

Sceptronema orientale Takano emend. E. A. Sar & I. Sunesen ( Figs 2–28 )

Iconotype: Figs 15 , 19 and 20 designated by Takano (1983).

Type locality: coastal waters off Shimoda City , Shizuoka Prefecture, Japan

Epitype here designated: Slide LPC 11650 (1)!, labeled “epitipo de Sceptronema orientale, Ría del Jabalí, 16/02/2009 ” (deposited in the Herbarium of the División Ficología “ Dr. Sebastián A. Guarrera ”). Sample LPC 11650!, used to prepare the epitype slide is also available in the Herbarium .

Epitype locality: Ría del Jabalí, Bahía Anegada, Argentina.

Description in LM: Cells are heteropolar in valve view and slightly wedge-shaped in girdle view, with a single, large, butterfly-like, valve-appressed chloroplast ( Figs 2–7 ). The cells are attached to individuals of the copepod Euterpina acutifrons by mucilaginous stalks of variable length, cells either solitary or forming linear chains ( Figs 2–7 , 11–14) by connecting the head-pole of the first cell of the chain to the head-pole of the next cell ( Figs 4, 6 ) and the foot-pole of this one to the foot-pole of the next one. The frustule shows two small septa restricted to the apical region in girdle view ( Figs 5, 7 , arrowheads). Valve is narrowly obovate, heteropolar, with a wide rostrate head-pole and a narrow capitate foot-pole, with central and straight sternum ( Figs 8–10 ), 31.0–59.0 µm long, 8.7–10.0 µm wide (maximum width). Striae are not visible. The girdle is narrower in the foot-pole than in the head-pole ( Figs 4–5, 7 ). Girdle bands are numerous ( Figs 8–9 ).

Description in SEM: Valve surface is flat ( Figs 15–17, 19–25 ), valve mantle is very shallow along the sides and deeper at the poles ( Figs 19–25 ). Sternum is conspicuous, central, narrow, straight, extending from pole to pole, slightly raised internally and spathulate at the ends ( Figs 21–23 ). Transapical striae are perpendicular to the sternum, uniseriate, evenly spaced, 40–50 in 10 µm, extending almost to the valve mantle edge ( Figs 19–25 ) except at the poles where they radiate from the end of the sternum ( Figs 21–23 ). Areolae are poroid, 40–45 in 10 µm, elliptical, a little elongated in transapical direction, externally and internally slightly sunken in the siliceous layer and externally occluded ( Figs 19–20 ). At each pole of the valve there is an apical slit field composed of longitudinal lamellae or bars with horizontal sunken cross bars ( Fig. 18 , arrowheads). The apical slit fields are restricted to the valve mantle. The head-pole field is composed of ca. 16 slits ( Figs 21, 23 ) while the foot-pole field is slightly smaller with ca. 12 slits ( Figs 22, 24 ). At the foot-pole there are 10 to 20 rimoportulae on the valve face and around the apical slit field in the valve mantle ( Figs 22, 24 , arrowheads). In addition to these, there is a row of 3 to 6 rimoportulae along each valve margin at the basal part of both valves ( Figs 20 , 25 , arrowheads). In only one valve of all analyzed valves an isolated rimoportulae is found at the head-pole ( Fig. 23 , arrowhead). The rimoportulae are internally sessile, rimmed all around, completely open, sub-circular to elliptical, inserted within the striae taking the place of two areolae ( Figs 22, 24–25 , arrowheads). Externally they open by sub-circular to elliptical pores without projection ( Figs 19 , 27 , arrowheads). The girdle bands that constitute each cingulum are numerous. Bands are open, tapered towards the ends, with splits nearly 180º apart at poles ( Fig. 16 ). Valvocopula is the widest band, 1.2–1.3 µm wide at the head-pole, open at the foot-pole, with a row of poroids in the pars interior throughout its length ( Figs 16 , 27–28 ) and several rows in the pars exterior in the head-pole that shorten towards the ends of the band ( Figs 18 , 27–28 ). Pars media is plain in external view ( Fig. 27 ) and thickened forming a longitudinal rib in internal view ( Figs 18 , 27–28 ), this rib becomes more prominent and widens in a very short septum at the head-pole ( Fig. 28 ). The width of the other copulae decreases in abvalvar direction and they are structurally similar to the valvocopula ( Fig. 18 ) but without septa at the head-poles. Abvalvar margin of all copulae is plain ( Figs 27–28 ).

Ecology: the species was only found attached on the exoskeleton of marine copepods by Takano (1983), Kimor et al. (1992) and Skovgaard & Saiz (2006). Fernandes & Calixto-Feres (2012) analysed epizoic diatoms on several species of copepods and they only found Pseudohimantidium pacificum Hustedt & Krasske in Krasske (1941: 272) on Euterpina acutifrons from Paranaguá Bay, Paraná State, Brazil.

In this study Sceptronema orientale occurred on Euterpina acutifrons in only two samples collected during the summer from Ría del Jabalí (LPC11650, 16 February of 2009) and Los Pocitos (LPC 11952, 4 March of 2014) enlarging its range of geographic distribution from Japan and the Mediterranean Sea to the coastal waters of the Southwestern Atlantic Ocean. A previous record of S. orientale from the phytoplankton of the Ribeirao da Fazenda, Santa Catarina State, Brazil, given by Souza-Mosimann & Moro Roos-Oliveira (1998) is a misidentification of another slightly heteropolar araphid diatom with a coarser stria density (15 in 10 µm) as seen in figure 45 of these authors.

Figures

FIGURE 2–10. Sceptronema orientale. LM. Figs 2–7. Sample LPC 11650. Figs 2–4. Several live colonies on Euterpina acutifrons. Figs 5–7. Details of these colonies. Fig. 5. Cells with one chloroplast, attached by mucilaginous stalks. Arrowheads show short septa. Fig. 6. Cells in valvar view with the head-pole attaching by a mucilaginous pad to the head-pole of the adjacent cell of the colony. Fig. 7. Cells in girdle view.Arrowheads show septa. Figs 8–10. Slide LPC 11650 (1), cleaned material, epitype here designated. Fig. 8. Complete frustule. Figs 9–10. Valves with girdle bands. Note the central, straight sternum. Scale bars: Fig. 2 = 100 µm; Fig. 3 = 50 µm; Figs 4, 6–7 = 20 µm; Figs 5, 8 = 10 µm; Figs 9–10 = 5 µm.

FIGURE 12–15. Sceptronema orientale on Euterpina acutifrons. SEM. Sample LPC 11650. Figs 11–13. Note cells attached to the copepod by mucilaginous stalks. Fig. 14. Detail of several coiled mucilaginous stalks. Fig. 15. Frustules tilted showing valvar and partial girdle views. Scale bars: Figs 11–12 = 100 µm; Figs 13–14 = 20 µm; Fig. 15 = 10 µm.

FIGURE 16–20. Sceptronema orientale. SEM. Sample LPC 11650. Figs 16–17. Internal valve view. Note open bands in Fig. 16 (VC valvocopula, CP 1 1st copula). Figs 18–20. External views. Fig. 18. Valve mantle of the head-pole with an apical slit field and girdle. Arrowheads show sunken cross bars of the slits (VC valvocopula, CP 1 1st copula, CP 2 2nd copula). Fig. 19. Foot-pole of a valve showing rimoportulae opening by subcircular to elliptical pores (arrowheads). Fig. 20. Central part of valve showing straight sternum and transverse, uniseriate striae. Scale bars: Figs 16–17 = 5 µm; Fig. 19 = 2 µm; Figs 18, 20 = 1 µm.

FIGURE 21–28. Sceptronema orientale. SEM. Sample LPC 11650. Internal views. Figs 21, 23. Head-poles showing apical slit field on the valve mantle. Figs 22, 24. Foot-poles showing apical slit field on the valve mantle and several rimmed, sessile rimoportulae (arrowheads).Fig. 25. Rows of rimoportulae near each valve margin. Note rimoportulae are inserted within the striae (arrowheads). Fig. 26.Apical slit field on the head-pole. Fig. 27. Foot-pole of the valve of fig. 16. Note valvocopula in internal view and the next copula in external and internal view (VC valvocopula, CP 1 1st copula). Fig. 28. Head-pole of the valve of fig. 16 showing valvocopula with a very short septum formed on the