Synedrosphenia gomphonema (Janisch & Rabenhorst) Hustedt, 1932 in Hustedt, 1931-1959

Lobban, Christopher S., Ashworth, Matt P., Camacho, Terance, Lam, Daryl W. & Theriot, Edward C., 2022, Revision of Ardissoneaceae (Bacillariophyta, Mediophyceae) from Micronesian populations, with descriptions of two new genera, Ardissoneopsis and Grunowago, and new species in Ardissonea, Synedrosphenia and Climacosphenia, PhytoKeys 208, pp. 103-184 : 103

Synedrosphenia gomphonema (Janisch & Rabenhorst) Hustedt, 1932 in Hustedt, 1931-1959

Figs 4 , 5

References.

Janisch and Rabenhorst 1863, p. 13, pl. 2, fig. 6; Grunow 1877, p. 169, pl. 194, fig. 3a, b, c, d; Peragallo and Peragallo 1897-1908, p. 313, pl. 78, figs 1, 2 (as S. cuneata Grunow); Hustedt 1914 in Schmidt et al. (1874-1959), pl. 305, figs 32, 33; Hustedt 1931-1959, p. 231, fig. 723; Cheng and Gao 2011, figs 147, 148; Hein et al. 2008, pl. 14, fig. 3, pl. 15, fig. 1; Hernández-Almeida et al. 2013, figs 39-42 (as Synedrosphenia cuneata ).

Description from literature.

The valve shape as shown by both Grunow (1877) and Hustedt (1914, 1931-1959) has a basal part with nearly parallel sides that then tapers wider, flaring more abruptly near the apical pole. Hustedt gave length as 250-475 µm, maximum width 27-36 µm, basal and apical stria densities 12 and 14 in 10 µm, respectively. Striae change abruptly from parallel to radiate where the apical pole narrows. Transapical costae on the virgae often continuous across the valve and obscuring the midline; a longitudinal rib near each margin. Round et al. (1990: 444) noted that in Synedrosphenia stria density is higher on the girdle bands than on the valve (Fig. 10A ), whereas in Climacosphenia it is lower on the girdle bands (Fig. 28A ). This holds true for all our species.

Materials examined.

Guam GU44Y-13!, GU44BD-4!, GU44BH-5!, GU 44BJ-2!, GU44BJ-4!. Federated States of Micronesia: Chuuk: TK28!; Yap: Y42-1!. Marshall Islands: Jaluit, J5!.

Observations.

Frustules heteropolar, cuneate in both valve and girdle view, numerous small, oblong plastids (Fig. 4A-D ). Valve margins parallel near basal pole, then gradually widening with slight flare below subrostrate apical pole (Fig. 4E, F ). Length 255->414 µm, greatest width 27-29 µm, stria densities in 10 µm 13-14 basal, 14-16 apical. Striae parallel except changing abruptly to radial at apical pole with several interpolated short striae (Fig. 4B, E, G ); areolae circular. Annulus near valve-mantle junction but clearly visible in both LM and SEM (Fig. 4B, E-I ), continuous around the poles (Fig. 4E, H, J ). Internal costae underlie annulus and virgae, except at the poles. Three girdle bands present (Figs 4F , 5A ). Valvocopula (Figs 4J, K , 5B-E ) with about 4 longitudinal rows of pores on pars exterior, decreasing to two near basal pole, pars interior with a fimbriate margin comprising a shelf with a single row of pores and a groove; poles with asymmetrical notch (Figs 4C, K , 5A ). Copula (Figs 4J, K , 5A, F, G ) pars interior with longitudinal line of pores along edge, the rest of pars interior plain with fringe of fimbriae, longer around apical and basal poles (Figs 4K , 5G ). Copula pars exterior abruptly narrowed at apical pole, pores arranged in ± decussate striae across the band reaching abvalvar margin and forming fimbriae; no pores around poles. Copulae in Guam specimens tending to form slits (Fig. 4D and Fig. 5A black arrows), not observed in Chuuk specimens (Fig. 5F, G ). Pleura visible as apical cap (Fig. 4F ), seemingly lost during cell division (Fig. 5A ; compare Fig. 12E, F ).

A frustule of Sceptroneis cuneata in remnants of Grunow 639 (Fig. 6 ), showed the valve and copula. Valve stria densities were lower than in our material: basal 12, apical 13 in 10 µm. The copula differed in having a hyaline abvalvar border with no tendency to form fimbriae (Fig. 6D, E ) and a longer hyaline area at the basal pole (Fig. 6E vs Fig. 4F ). The apical cap of the pleura may be smaller than in our specimens. A valve apical pole with part of the valvocopula (Fig. 6F, G ) had 11 striae in 10 µm and there were no pores in the exterior, in contrast to Guam specimens.

Taxonomic comments.

There are too many differences from Grunow’s specimens to identify our species as Sceptroneis cuneata . We also cannot confirm whether our specimens match Synedrosphenia gomphonema without SEM of authentic specimens. The taxonomy of Synedrosphenia is convoluted. As explained by Fourtanier and Kociolek (1999):

" Originally described (and validly published) as a subgenus of Synedra : Synedra subgenus Synedrosphenia H. Peragallo in H. and M. Peragallo 1900 [ Peragallo and Peragallo 1897-1908], p. 308, 312. Three species were included, Sceptroneis [ Synedra ] Synedra cuneata Grun., S. clavata Grev. and S. dubia Grun. and no type was designated. Although Azpeitia 1911, p. 220 introduces the name as "El genero ó subgenero Synedrosphenia " (the genus or subgenus Synedrosphenia ), he treats it as a genus when describing his new species Synedrosphenia giennensis . Although S. giennensis Azpeitia is the only species formed as binomial with Synedrosphenia in Azpeitia 1911, Azpeitia, in his treatment of Synedrosphenia also clearly included the 3 species that constituted Peragallo’s subgenus (but did not make transfers to genus Synedrosphenia ). No type was designated by Azpeitia. The generic name cannot be attributed directly to Azpeitia because he did not provide a generic description. The authorship of Synedrosphenia is therefore "(H. Peragallo in H. Perag. and M. Perag.) Azpeitia," and the type has to be chosen among the species originally included in the subgenus by Peragallo. The choice of S. giennensis as the type species by Round, Crawford and Mann (1990) p. 444 and 704 is therefore untenable. "

Hustedt (1931-1959) very clearly synonymized Sceptroneis cuneata into Synedrosphenia gomphonema (1931-1959, fig. 723, pp. 220-221 in Jensen’s (1985) translation, pp. 241-242 in orig.). The drawing in Janisch and Rabenhorst (1863) is, as Hustedt (1931-1959) said, "very schematic and erroneous to be sure," showing a prominent sternum, but Hustedt based his synonymy on examination of many specimens from both Janisch and Grunow, both of whom worked on collections from Honduras. The other two species, S. clavata and S. dubia , are poorly known, perhaps not seen since their original descriptions, both characterized as very rare, and perhaps not even attributable to this genus. We thus propose Sceptroneis cuneata Grunow as the lectotype, below, recognizing the synonymy with S. gomphonema as the current name for the Honduras species, but pending evidence from Janisch and Rabehnorst’s materials to test whether our species is the same. Synedrosphenia giennensis Azpeitia (1911, p. 219, pl. 6, figs 1, 2) was based on LM of a single clavate valve, maximum width ¼ of the way from one end, costae between striae not always continuous across the valve. Azpeitia made no mention of longitudinal costae. The dimensions were 195 × 35 µm, 12 striae in 10 µm, areolae 19-20 in 10 µm. This does appear to belong in Synedrosphenia but certainly needs further study.

Figures

Figure 4. Synedrosphenia gomphonema A live specimen in valve view showing heteropolar cell shape and plastids (GU 44 BJ- 4) B apical portion of cleaned valve in LM showing change in stria orientation where cell narrows (GU 44 BD- 4) C, D recently divided frustule in girdle view with details of basal and apical poles, respectively, showing heteropolarity; black arrow indicates slit formation on the copula (GU 44 BJ- 4) E, F valvar view of frustule at 0 ° and 60 ° tilt, respectively, arrows on E showing location of annulus, labels on F naming the girdle bands (abbreviations as before) G-I apical and basal portions of valve, internal view tilted 60 °, showing pseudosepta at poles (H, I arrows) and transverse and longitudinal costae (TK 4); inset (H) shows tip of same valve at 0 ° tilt with lack of costae between the last few striae but continuation of annulus J, K basal portions of a broken, recently divided frustule from Chuuk, viewed at 0 ° and 60 ° tilt, respectively, valves and girdle bands of one daughter cell with one valve of other daughter on top; arrow shows the notch between valve and valvocopula (TK 4). Scale bars: 25 µm (A); 10 µm (B-G, I); 5 µm (H, J).

Figure 5. Synedrosphenia gomphonema cont. A apical pole of frustule in polar view tilted 60 °, showing the valvocopula and copula of the hypocingulum (HVC and Hcop) largely hidden under the epicingulum bands (EVC and Ecop); the pleurae are missing and in the space where they were the tips of the newly formed valves are visible (long arrows). Short white arrows point to the apical notches slightly off-center in opposite directions; black arrow shows some slit formation in the copula (GU 44 BJ- 4) B-E valvocopula with apical pole in advalvar view (B) showing recurved pars interior at the tip, abvalvar view (C), basal pole (D) and middle (E), all showing fimbriae (B, D, E from same specimen in GU 44 BI- 4, C from TK 4) F, G copula middle and apical pole, respectively, external view, showing fimbriae developing on the abvalvar edge of the pars exterior (arrow) (TK 4). Scale bars: 10 µm (A, E, F, G); 5 µm (B-D).

Figure 6. Specimens of Sceptroneis cuneata from Grunow's Honduras sample A-C whole frustule at 0 ° tilt and details of basal pole and apical poles, respectively, showing internal costae and the copula; arrows point to long fimbriae overlapping valvocopula at both poles D, E same specimen, tilt = 60 °, details of apical and basal poles, respectively, showing copula, including shallow cut-away matching smaller pleura (arrow on D), hyaline abvalvar margin of copula (black arrow on D), and reduced poration near basal pole (arrow on E) F apical part of valve in external view G valvocopula associated with same specimen. Scale bars: 50 µm (A); 10 µm (B-F); 5 µm (G).

Figure 10. Synedrosphenia licmophoropsis sp. nov., girdle bands A, B frustule in girdle view with thecal elements labeled, respectively on the apical part and the basal pole of the same cell also showing the asymmetrical apical notches in the valvocopula (arrows) (GU 55 D- 3) C small portion near middle of frustule where pleura (pl) is exposed (GU 76 B- 2) D, E basal pole of valvocopulae at 0 ° tilt with opposite valve in the background and tilted to show complex shape of the pars interior, arrowhead pointing toward notch (GU 76 B- 2 and TK 4, respectively) F portions of valvocopula and copula showing fimbriate inner edges (GU 55 D- 3) G valvocopula, apical pole in abvalvar aspect with attached valve, showing elongated pores on inner edge (arrow) (GU 44 BJ- 2) H apical portion of copula showing very long fimbriae at the tip (arrow) (GU 55 D- 3) I relationship between first two girdle bands at basal pole, the long fimbriae of the copula overlapping the valvocopula (GU 76 B- 2). Scale bars: 10 µm (A, B, F, H); 5 µm (C-E, G, I).

Figure 12. Synedrosphenia parva sp. nov., cont. All GU 75 A- 4 A, B valvocopula showing apical internal side from abvalvar position, and portion of middle from advalvar side, respectively, showing row of pores along base of pars interior and fimbriae C internal view of apical pole with valvocopula in situ and the copula, broken in the middle, covering the valvocopula around the apical pole and left side D basal pole of same specimen, again showing the long fimbriae overlapping the valvocopula E, F frustules tilted to show polar (apical) architecture of, respectively a recently divided cell, where the pleura is in place between the copulae of the two cingula, and a non-dividing cell G detail of a pleura loosened from its position and showing some of the fimbriae (still tucked under the copula at top of image). Scale bars: 10 µm (A); 5 µm (B, D-F); 2.5 µm (C, D, G).

Figure 28. Climacosphenia elegantissima sp. nov., cont. GU 52 U- 2 (A), GU 52 X- 1 (B, C), GU 44 AI- 5 culture (D), GU 52 AI- 1 (E) A whole mount of frustule apical pole in girdle view, showing two girdle bands, patch of irregular areolae on the valve mantle (arrow), spines (arrowheads) B part of valvocopula broken away and showing a solid circular cross-section of the craticular bar (arrowhead) and well-developed fimbriae (arrow) C portion of valvocopula from stem, showing double craticular bars, ingrowths from opposite sides D apical pole with valvocopula showing porous bands of silica around several craticular bars E detail of copula showing stria density and fimbriate margin on pars interior. Scale bars: 10 µm (A, D, E); 5 µm (B, C).