Toxarium undulatum J.W. Bailey, 1854

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 undulatum J.W. Bailey, 1854

Figs 23 , 24

References.

Bailey 1854, p. 15, plate (1), figs 24, 25; Peragallo and Peragallo 1897-1908, p. 314, pl. 78, fig. 7; Hustedt 1931-1959, p. 222, 224, fig. 714; Güttinger 1991 (both as Synedra undulata ); Poulin et al. 1986, figs 33-36; Hein et al. 2008, p. 33, pl. 15, fig. 3; Lobban et al. 2012, p. 260, pl. 17, figs 6-8; Álvarez-Blanco and Blanco 2014, p. 128, pl. 63, figs 4-6.

Description from literature.

Toxarium undulatum , the generitype, was said to differ only in the wavy outline of the valve ( Hustedt 1931-1959), stria density rarely reported but Peragallo and Peragallo (1897-1908) state 12 in 10 µm. The outline in Bailey’s (1854) plate is shown as undulating with a long wavelength, in Peragallo and Peragallo (1897-1908), with a shorter wavelength, and in Hustedt (1931-1959) the center clearly has a wavy edge but the “horns” are scarcely undulate. Micrographs in recent works ( Witkowski et al. 2000; Hein et al. 2008) show distinctly undulate outlines. In the SEMs shown by Poulin et al. (1986) we count 19-21 striae in 10 µm, whereas Güttinger (1991: 2.01.30-10) shows specimens with lengths of 485 and 580 µm, widths 8 µm at center, 5 µm at poles, but with 12 striae in 10 µm. Lobban et al. (2012) reported lengths of 270-400 µm, widths 5-9 at the center, 6 µm at poles, 4 µm in between, with some specimens having virtually no central inflation; no stria density stated but their fig. 7 shows 12-13 striae in 10 µm. T. undulatum has usually been illustrated as straight but curved specimens are shown by Hein et al. (2008) and Lobban et al. (2012). The genus was emended by Poulin et al. (1986), whose SEM images of T. undulatum show an asymmetrical polar pseudoseptum and internal transverse costae "in parts of the valve between the poles and the center and sometimes anastomosing" (also shown in Güttinger 1991). The T. undulatum from Guam (GU44S / HK210 / ECT 3802) used by Ruck et al. (2016) showed very shallow undulations, at least after culture, and additional images of the voucher stub show that it has a single row of areolae on the mantle (Suppl. material 4: Fig. S2A-C), so we would therefore identify it as T. hennedyanum . A similar specimen from wild material is also shown in the Suppl. material 4: Fig. S2D-F.

Materials examined.

Guam: GU44X-2!, GU44Z-15!, GU44BJ-4!, inter alia; Federated States of Micronesia: Chuuk, TK28 !; Yap, Y36-2!, Y42-3!. Marshall Islands: Majuro, M1!, Jaluit, J5 !

Observations.

Valves straight or commonly curved overall, strongly sinusoidal along the narrow part, the oval central portion with a wavy outline, apical portions straight sided (Fig. 23A, B, F ), length 255-326 µm, width 5 µm at poles, 7 µm at the center, 3 µm in between, stria densities 14-17 in 10 µm (Fig. 23C-I ). Mantles deep with typically 3-4 areolae in the stria there (Fig. 23H, I, K ). Spines absent. Valvocopula plain except for single row of pores along the base of the pars interior, fimbriate edge to pars interior (Fig. 23G ), knuckle-like structure at poles, as in T. hennedyanum (Fig. 23K , compare with Fig. 22F ). Copula with a regular pattern of small areolae on the pars exterior, forming striae consistently 34 in 10 µm (Fig. 23H-J, L ), in which the pars interior, while similar to that of T. hennedyanum near the poles, quickly becomes a fringe of short, narrow fimbriae with a line of triangular pores along the junction with the pars exterior (Fig. 23H ). The narrow pleura was largely or entirely obscured (Fig. 23L ) (this pole identified as T. undulata by 2+ rows of areolae on the mantle, and pores on the poles of the copula; contrast Fig. 22H ); a small exposed portion showed a fimbriate edge (Fig. 23M ).

We also documented T. undulatum in Grunow’s Honduras sample (Fig. 24 ). A whole valve was 700 µm long (Fig. 24A ) with long-wavelength undulations. The deep mantle sometimes exhibited longitudinal waves in the areolae (not solely an artefact of the wave in the valve, shown by short additional longitudinal lines of areolae-Fig. 24D , arrows). The striae on the valve face were two areolae long on each side bordering scattered areolae in the inflated center and poles (Fig. 24C, E ), internally, the virgae were thickened into costae (Fig. 24C ). Valvocopula (Fig. 24C, E-G ) with a single line of areolae on the exterior, short fimbriae along the interior margin except at the sculpted poles, and a series of arched slits (Fig. 24F, G ; compare Fig. 23K ). Copula (Fig. 24C-E, H ) wide with coarse fimbriae on the pars interior, forked at the tips, exterior with striae of pores tending to merge into slits, especially on the advalvar side. Fimbriate pleura clearly seen in Fig. 24H .

Taxonomic comments.

The specimens from Grunow’s Honduras material are near the length ("about 35m" = 890 µm; see Itaki and Bjørklund 2006) and shape described by Bailey (1854) for specimens from Sargassum in Narragansett Bay. As noted by Hustedt (1931-1959), Grunow (1877) did not mention this species (in the context of presenting new species), but Hustedt says he observed it on Grunow’s slides.

In the Micronesian samples, depths of the mantle, and structure of the copula were different in the two species, so we can assert that the specimens shown here for T. hennedyanum and T. undulatum are different species. The large genetic variation in Toxarium materials we have sequenced (Fig. 33 ) casts doubt on whether either of them might be identified to authentic Atlantic types, a question highlighted by the Grunow specimens. It similarly raises questions about the number of species there might be in Micronesia. Both questions require much more work to define the range of character states and their combinations, but the oft-repeated claim that the two species differ only in outline is already not supported by morphological evidence. The more important point for the present study is to establish generic characters for comparison to those of the genera in Ardissoneaceae and Climacospheniaceae .

The Toxarium spp. specimens shown here from sample GU44BJ-4 were in a community with the new species Ardissoneopsis gracilis (see above), which has a slightly undulate outline but is distinguished from T. undulatum by the cuneate girdle view, regular striae across the valve face, apical spines, and the decussate pattern of pores on the girdle bands (Fig. 18 ). Also present were Synedrosphenia gomphonema , S. crystallina , Ardissoneopsis fulgicans , A. appressata , and Grunowago pacifica .

Figures

Figure 18. Ardissoneopsis gracilis sp. nov. (GU 44 BJ- 4, except B TK 28) A-C three specimens to scale in LM to show size range: valves from Guam (A) and Chuuk (B), frustule from Guam in girdle view (C) showing heteropolarity D frustule in SEM tilted 60 °, showing both valve and girdle faces E, F pole and mid-section of holotype G-K external views of valve in SEM with other species adjacent for comparison (GU 44 BJ- 4): index image (G) with locations of details marked, apical pole (H) (shown by depth of mantle), compare stria density with Ardissoneopsis appressata (A. g.); top half of center (I), offset areolae in striae within the oval suggest location of annulus; narrow portion below center (J), compare with scattered areolae in adjacent Toxarium undulatum (T. u.); basal pole (K), note spines on both poles L, M internal aspect near middle and at the apical pole, showing lack of costae N, O girdle view of frustule apical and basal poles, showing taper in mantle and girdle bands P possible piece of pleura (pl?) with fimbriae Q, R fimbriate edges of valvocopula and copula, respectively. Scale bars: 50 µm (A-D, G); 10 µm (E, F, H-K); 5 µm (L-R).

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 24. Toxarium undulatum from Grunow's Honduras material A, B entire valve, 700 µm long, and detail of central portion, showing long-wavelength undulations C portion with the central inflation, showing mantle depth, internal costae, valvocopula and copula (stria density 14 in 10 µm) D frustule in girdle view, showing vertical wave in rows of areolae with inserted arcs (arrows); notice also the different depths of the two mantles (stria density 17 in 10 µm) E portion of valve with copula and valvocopula F, G valvocopula pole, abvalvar and advalvar surfaces, respectively, showing series of arched slits (compare with Fig. 22 F) H pole of frustule showing fimbriate pleura and notch in valvocopula. Scale bars: 100 µm (A); 25 µm (B); 10 µm (C-E); 5 µm (F-H).

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.