Toxarium hennedyanum (Gregory) Pelletan, 1889

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

Toxarium hennedyanum (Gregory) Pelletan, 1889

Fig. 22

References.

Hustedt 1931-1959, p. 222, 224, fig. 713 (as Synedra hennedyana ); Round et al. 1990, p. 422-423; Lobban et al. 2012, p. 260, pl. 17, figs 1-5; Kooistra et al. 2003, fig. 1A-R (as T. undulatum ); Hein et al. 2008, p.33, pl. 15, fig. 3; Álvarez-Blanco and Blanco 2014, p. 128, pl. 63, figs 4-6.

Description from literature.

Colonial on stout mucilage stalks. Long, narrow valves, usually straight, inflated at the poles and the middle, valve lengths ranging from 300 to>1000 µm ( Álvarez-Blanco and Blanco 2014); widths 6-8 µm in the middle, 5-6 µm at poles, and about 2 µm elsewhere; transapical striae very short, 9-11 in 10 µm, with scattered areolae in wider central and polar areas ( Hustedt 1931-1959). Lobban et al. (2012, pl. 17, figs 4, 5) illustrated variants with few/no pores in the central part of the valve face. Girdle bands are all closed ( Kooistra et al. 2003). The valvocopula has a single row of pores along junction between the pars interior and pars exterior and an asymmetrical, notched shelf that fits against the pseudoseptum. The copula has striae that are either porate or become slit-like with broadly fimbriate margins of the pars interior (compare their fig. 1I, L with our Figs 22J , 23J ). The narrow pleura has a single row of pores along the junction between the pars interior and pars exterior.

Materials examined.

Guam: GU21AK-11!, GU44AK-4!, GU44BJ-4!. Federated States of Micronesia: Chuuk, TK28!. Marshall Islands: Majuro: M1!; Jaluit: J5!; Bikar: BA2!; inter alia.

Observations.

Valves 156-334 µm long, usually straight but sometimes curved, 7 µm wide at middle, 4-5 µm at poles, with a single row of areolae on the shallow mantle (Fig. 22H, J , asterisk) and two rows before the scattered areolae (Fig. 22B, D, I ), making the short transverse striae 3 areolae long; stria density 10-14 in 10 µm (Fig. 22A, B, D, I, J ). In the context of the present analysis, we confirm the presence of an asymmetrical pseudoseptum (Fig. 22E ), asymmetrical valvocopula poles with apical notch (Fig. 22F-H ), valvocopula finely fimbriate (Fig. 22I ), and the copula structure tending toward slits, the striae 28 in 10 µm at the poles (Fig. 22G ) increasing to 36 in 10 µm with broadly fimbriate pars interior (Fig. 22J ). There is a knuckle-like series of arched slits on the valvocopula pars interior (Fig. 22F ), different from the structure in Synedrosphenia (compare with Fig. 8B and Fig. 10D, E, G ). Spines absent. We note that the pars exterior of the copula is hyaline around the poles. However, the fine fimbriae on the pars interior of the valvocopula (Fig. 22I ) are absent from the specimens in Kooistra et al. (2003 fig. 1J, K). A pleura was present (Fig. 22H ), the pars interior also fimbriate (not shown).

Taxonomic comments.

Kooistra et al. (2003) show a single row of pores on the mantle and a copula that matches those shown here for T. hennedyanum . They do not state a stria density, but we count 11 in 10 µm, measured from their fig. 1E. There has been a tendency to ignore stria density, reflecting the marginal striae and the domination of the valve face by scattered areolae. Kooistra et al. (2003) had monoclonal cultures in which both Toxarium hennedyanum -like and Toxarium undulatum -like cells were present, and they proposed a merger of the two species. The specimens they show had a rippled edge, but not a strongly wavy outline (contrast Poulin et al. 1986; Hein et al. 2008, and our Fig. 23 ); i.e., a midline along the apical axis is straight, whereas that in T. undulatum is sinusoidal. If the Micronesian specimens shown here are indeed T. hennedyanum and T. undulatum (by no means certain), our results would suggest that the rippled edge seen in the cultures of Kooistra et al. (2003) was a phenotypic expression of T. hennedyanum and was not T. undulatum. We previously noted ( Lobban et al. 2012) the significant genetic variation in Guam isolates of T. hennedyanum and T. undulatum reported by Theriot et al. (2010, 2011) and this is even more evident now; however, in reviewing the vouchers, we find no data from specimens attributable to T. undulatum ; all the variation shown in Fig. 33 appears to be part of a T. hennedyanum complex.

Figures

Figure 8. Synedrosphenia bikarensis, cont. A-C valvocopula: apical portion in advalvar view (A) with asymmetrical notch at apical pole (arrow), middle portion (B) with long sturdy fimbriae (ext = external surface, int = internal surface), and basal portion in girdle view (C) D, E internal views of apical and basal poles, respectively, of same valve with valvocopula, showing opposite asymmetry of the notches (arrows) F basal portion of valve with attached girdle bands, showing how the copula fimbriae fit over the valvocopula at poles (arrow) G apical portion of copula showing poration. Scale bars: 5 µm.

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 22. Toxarium hennedyanum, all from GU 44 BJ- 4 except C GU 21 AK- 11, and I, K culture from GU 44 AK- 4 A LM of valve with typical pattern in central area; 9 stria in 10 µm B SEM of a valve from same sample, 12 striae in 10 µm, with reduced central area C mucilaginous stalks with clusters of cells D internal central area, showing lack of costae E, F internal pole of valve showing asymmetrical pseudoseptum (arrow) and valve with valvocopula showing similar asymmetry (arrow) G pole of frustule in girdle view showing apical groove (arrow) on valvocopula and fimbriae partially exposed on copula H pole of frustule in girdle view showing apical notch (arrow) and the pleura (pl); note single row of areolae on mantle (*) I pole of valvocopula in girdle view, fimbriae absent from the tip J narrow portion of valve showing structure of copula (compare with Fig. 23 J) and single row of pores on mantle (*) K pole of copula in girdle view showing long fimbriae. Scale bars: 50 µm (A-C); 10 µm (I); 5 µm (D-K).

Figure 23. Toxarium undulatum (all from Guam, GU 44 BJ- 4) A, B entire valves in LM and SEM, respectively, showing prominent undulation C, D central expanded portion external and internal views, respectively, the latter showing costae E pole, internal view showing asymmetrical pseudoseptum (arrow) F internal and external aspects of valve in the narrow part G valvocopula lying inside narrow part of valve H, I portion of frustules in girdle view, showing multiple rows of pores on mantle, valvocopula with apical notch (arrow), and copula with pores continuing around the pole (arrowhead) J detail of copula, for comparison with Fig. 22 J K pole of valvocopula showing arched slits L frustule in girdle view showing pleura M fragment of the pleura, showing fimbriae. Scale bars: 50 µm (A, B); 10 µm (C); 5 µm (D-I, K); 2 µm (J, K, M).

Figure 33. Phylogenetic trees resulting from three analytical methods of the 3 - gene DNA sequence dataset assembled for this manuscript. Only the Ardissoneaceae and their sister group in the molecular phylogeny, Lampriscus, is shown here-the complete trees can be found in Suppl. materials 5 - 7: Figs S 3 - S 5 A Maximum Likelihood phylogeny resolved by RAxML, where values at nodes are bootstrap support values B Maximum Likelihood phylogeny resolved by IQTREE, where values at nodes are bootstrap support values C Bayesian Inference phylogeny resolved by ExaBayes, where values at nodes are posterior probability values. Strain taxonomy (name followed by DNA voucher ID or strain ID) follows currently accepted classification, with proposed genera based on morphology shown to the right of strain ID.