Guarreraea stipata (Frenguelli) Kociolek & Guerrero, 2018

Guerrero, J. M., A. A. Vouilloud, Sala, S. E., Kociolek, J. P. & Vijver, B. Van De, 2018, New species and a new genus of the Orthoseirales from Patagonia, Argentina, with comments on systematic affinities within the Order, Phytotaxa 345 (2), pp. 119-132 : 129-131

Guarreraea stipata (Frenguelli) Kociolek & Guerrero comb. nov.

Basionym: Cyclotella stipata Frenguelli 1942 , XVII Contribución al Conocimiento de las Diatomeas argentinas. Diatomeas del Neuquén (Patagonia). Revista del Museo de La Plata (n.s.) 5, Botánica 20: 213, fig. 2 and Pl. XII; figs 5–6.

Emended diagnosis:—Valves rounded showing an irregular ring of small marginal spines, broadly expanded at the base. Valve dimensions (n=115): diameter 14–69 μm. Striae on the valve face of varying length, 12–19 in 10 μm, composed of rounded areolae, 12–19 in 10 μm. Central area composed of a hyaline area with 4–11 carinoportulae. Rimoportulae openings round or radially elongated, located between the carinoportulae. Small spinules irregularly scattered on the valve face, clearly visible in SEM. Mantle striae parallel to the pervalvar axis, 14–18 in 10 μm, composed of relatively small areolae having identical sizes along the entire striae, 15–20 in 10 μm. Interstriae on the valve mantle not thickened. Collum unornamented. Internally, rimoportulae openings narrow, bordered by thin thickenings on both sides.

Type: — ARGENTINA. Neuquén: small creek near international milestone Paso de Pino Hachado. J. Frenguelli, 2 March 1941 (lectotype (designated here) Collector Frenguelli. Slide 428(4), finder X 45(1), here illustrated as Figs 3– 4 ). Our designation of a lectotype is justified since although Frenguelli did illustrate his new species, and an illustration can be a holotype ( Blanco 2016), he provided more than one illustration, and therefore no holotype. We rectify this situation by designating a lectotype here.

G. stipata is probably aerophilic since it was more abundant in mosses and peatbogs in small creeks; its occurrence, always in low abundances, in plankton net samples from rivers and streams may be due to washing-off from the margins.

Table 2: Morphometric and morphologic data of different populations of “ Cyclotella stipata ”. Comparison with Orthoseira limnopolarensis .

In considering the relationships of this taxon with Orthoseira we may also take into account the allied genus Cavernosa that has marginal caverns as in some Orthoseira species ( Cremer et al. 2011; see also Hagelstein 1939, plate 6, figs 4, 5 for the taxon “ Melosira roseana f. porocyclia (Ehrenb.) Grun. ”). Cremer et al. (2011) discussed similarities and differences between these two genera and separated them based on the presence of carinoportulae and rimoportulae respectively. The presence of both structures in G. stipata and G. limnopolarensis suggests that Cavernosa is part of the lineage recognized as the Orthoseirales , even though it lacks one of the features used to diagnose the group, that is, presence of carinoportulae ( Round et al. 1990). Cox (2015) reached a similar conclusion in her recent treatment of diatoms. There are several situations in diatoms where this appears to be the case. For example, although the diatom genus Gomphoneis Cleve (1894: 73) is diagnosed in part by the presence of an internal lamina of silica on the mantle of the valves (termed ‘marginal lamina’) ( Kociolek & Stoermer 1989, 1993), a large species flock in Lake Baikal, as well as the widely distributed species G. olivacea (Hornemann) P.A. Dawson ex Ross & Sims (1978: 162) and G. olivaceoides (Hustedt) Carter in Carter & Bailey-Watts (1981: 566), among others, have apparently secondarily lost the feature ( Kociolek & Stoermer 1989, 1993). Another example is the diatom genus Diprora Main (2003: 261) , endemic from Hawaii, described as a member of the Fragilariaceae due to lack of a raphe ( Main 2003). The only species of the genus, D. haenaensis Main (2003: 261) , was cultured and the lack of a raphe system in all parts of its life cycle was confirmed, but a multi-gene phylogenetic analysis showed it to be deeply embedded within the raphid diatoms, most closely allied with members of the Sellaphoraceae ( Kociolek et al. 2013) . Thus, even though Diprora has no raphe system, probably through secondary loss, it should be classified among the raphid diatoms and not in the phylogenetically distant Fragilariaceae .

An interesting feature is the presence of internal slit-like structures at the valve center in several Orthoseira species. These structures are bordered by a narrow, barely thickened margin and apparently do not open to the exterior. They are particularly distinct in O. gremmenii ( Van de Vijver & Kopalová 2008) and have also been observed in the new species described in this study. Further analysis is needed to elucidate their possible relationship with the rimoportulae present in Guarreraea .

Figures

FIGURES 1–14. “Cyclotella stipata Frenguelli”. LM. Specimens from the type population. 1–9. Valve views showing population variability. 10. Detail of valve face, note the hyaline area at center with the ring of carinoportulae (arrowhead) alternating with rimoportulae (arrow). 11–12. Frustule in girdle view, showing the smooth collum and the internal thickening at the mantle margin. 13. Valve in girdle view, note the copulae ligulated with distinct poroids. 14. Frustules in girdle view showing linking spines. Scale bars: Figs 1–14 = 10 μm; bar length is the same in all figures except Fig. 10.