Psammothidium hainanii Kociolek & Liu, 2014

Liu, Yan, Kociolek, John Patrick, Wang, Quanxi, Tan, Xiang & Fan, Yawen, 2014, Two new species of monoraphid diatom (Bacillariophyceae) from South of China, Phytotaxa 188 (1), pp. 31-37 : 32-35

Psammothidium hainanii Kociolek & Liu sp. nov. ( Figs 1–6 , 17–22 )

Type: — CHINA. Stream, Orchid valley in Crescent Dragon Bay National Forest Park, Hainan Province. Collected 14 th February 2012, Liu Y. & Li L.X. ( HANU, slide THHN2012013 , holotype! = Figs 3 and 4 ; COLO HN13 , isotype!) .

LM: Valves broadly elliptical, abruptly constricted at apex, forming narrowly-protracted, rostrate ends, 24–30 μm long, 10–12 μm wide. Raphe valve with raphe straight, external proximal raphe ends slightly expanded, external distal ends curved in opposite directions. Axial area narrow, central area asymmetrical, rectangular, not reaching margins. Rapheless valve with axial area linear widening into an asymmetrical, rectangular central area, not reaching margins. Striae radiate, 22–24 in 10 μm on both valves.

SEM: Raphe valve, externally, raphe straight with slightly dilated external proximal ends positioned in a shallow groove, external distal raphe ends reach the margin and curve to opposite sides. Striae uniseriate, areolae small, round becoming slit-like near margin. One row of slit-like areolae present on mantle. Internally, proximal raphe endings curve to opposite sides, large helictoglossae raised at the end of the raphe. Areolae covered by hymens. Striae uniseriate on rapheless valve, individual areolae larger than on raphe valve, nearly elliptical, somewhat elongated near axial area and margin. Internally, sternum slightly raised. Areolae occluded by hymens.

Etymology:— Named for the type locality.

Ecology:— The type locality for Psammothidium hainanii is a small stream in the Orchid valley in Crescent Dragon Bay National Forest Park, an area visited by many tourists. Psammothidium hainanii occurs with other species of Pinnularia Ehrenberg (1843: 45) and Navicula ( Bory 1822: 128) . Psammothidium hainanii was also found in a sample collected from a stone in another part of this stream. In the latter sample, Psammothidium hainanii occurred with species from several genera, including Urosolenia Round & Crawford (in Round et al. 1990: 324, 679), Pinnularia and Gomphonema Ehrenberg (1832: 87).

Oberservations: — Psammothidium hainanii is distinguished from other species in Psammothidium by its valve outline. Only Achnanthes exigua var. heterovalvata f. angustirostrata Krasske (1939: 371 ; see also Lange-Bertalot et al. 1996), described from Chile, and shares some similar features, but it has a more slender, acute headpole ( Krasske 1939; Lange-Bertalot et al. 1996) and lacks the structure of the central area on the rapheless valve seen in Psammothidium hainanii .

μm. Fig. 22 . Internal view of the raphe valve, showed the opposite curved proximal raphe endings, scale bar = 5μm.

Platessa guangzhouae Liu & Kociolek sp. nov. (Figs 7–16, 23–26)

Type:— CHINA. Stream, Sanyatang valley in Guangzhou Province. Collected 7 th February. 2012, Liu Y. & Li L.X. ( HANU Slide THGZ2012017 , holotype! = Figures 9 and 10; COLO, GZ17 , isotype!) .

LM: Valves elliptical, 13.5–20.0 μm long, 5.6–7.3 μm wide. Raphe valve with very narrow, linear axial area, widening into a bow-tie shaped central area, not reaching valve margins. Raphe straight, with dilated external proximal raphe ends and straight distal ends. Striae on raphe valve fine, slightly radiate, 20–24 in 10 μm. Rapheless valve with wide lanceolate axial area, almost 1/3 of valve width, bordered by short and broad striae, 11–12 in 10 μm.

SEM: Raphe valve, externally, proximal raphe endings straight, slightly expanded and positioned in a shallow groove, distal raphe endings larger and expanded. Areolae uniseriate, small and round, becoming larger towards margin. All striae terminate at a longitudinal line between striae and margin. One row of round areolae occurs along margin. Internally, proximal raphe ends deflect to opposite sides, raised helictoglossae occur at ends of valve, areolae covered by hymens. Rapheless valve, areolae externally uniseriate, small, short and slit-like. Valve ribbed internally between striae, areolae larger, round, occluded by hymens.

Etymology: —Named for the type locality.

Ecology: — The type locality for Platessa guangzhouae is a stream in the forest of Sanyatang Valley , Guangzhou province , China, where it is rare. Overall , species diversity in this sample was not high (a new species of Stenopterobia Brébisson & Van Heurck (1896: 374) was found and will be published later). The dominant species is Frustulia crassinervia (Brébisson) Lange-Bertalot & Krammer in Lange-Bertalot & Metzeltin (1996: 57). Other small and unknown species of Eunotia Ehrenberg (1837: 44) and Brachysira Kützing (1836 : no. 153) are also present .

Observations: —Our specimens appear similar to species of Psammothidium taxa, as they have uniseriate areolae on both valves. The valves, however, are flat, lack terminal fissures, have a hyaline ring along the margin, and there is a single areola at the end of each stria. These features are obvious differences that separate our species from Psammothidium . Although the original description of Platessa states that the striae are mostly biseriate with only a “tendency” to have uniseriate striae ( Potapova 2012), the present features of our specimens strongly indicated it to be different from typical species of Psammothidium and better placed in Platessa . Platessa guangzhouae is very similar to Platessa lutheri (Hustedt) Potapova (2012: 33 ; basionym: Achnanthes lutheri Hustedt 1933: 405 , fig. 858), especially in LM, since both have the raphe valve with fine striae, a bow-tie shaped central area and the rapheless valve with short and broad striae. In SEM, both have uniseriate areolae, straight proximal raphe ends located in a shallow groove and drop-like distal endings on the raphe valve ( Potapova 2012). Platessa lutheri , however, is smaller (8–17 μm long, 4.5–6.0 μm wide, Potapova 2012) and has biseriate areolae on the rapheless valve. Another species with uniseriate areolae on the raphe valve is Platessa kingstonii Potapova (2012: 35) ; it differs from P. guangzhouae by its smaller size (7.4–11μm long, 4.4–5.0μm wide), rectangular central area on the raphe valve and the wide elliptical—lanceolate axial area on the rapheless valve ( Potapova 2012). The rapheless valve has multiseriate striae in P. kingstonii , but the striae are composed of uniseriate rows of areolae in P. guangzhouae . Achnanthes saxonica Krasske in Hustedt (1933: 403; see Patrick & Reimer 1966: 265, pl. 17, figs 13–14) is also similar since it has finely lineate striae on the raphe valve and more or less distinctly lineate striae on the rapheless valve. However, it is smaller (8–13 μm long, 4–5 μm wide, Patrick & Reimer 1966) and the axial area on the rapheless valve is narrower. Achnanthes oblongella Østrup (1902: 252 ; see Krammer & Lange-Bertalot 2004: pl. 16, figs 1–14), first reported from Thailand, also resembles Platessa guangzhouae , as the raphe valve of the two species are similar; Platessa guangzhouae has a wider axial area on the rapheless valve.

A very distinctive character of Platessa guangzhouae is the broad appearance of the striae on rapheless valve in LM (although they are uniseriate in SEM). The striae are broader than any kind of uniseriate striae in any of the known species of Psammothidium and Achnanthidium. The wide costae (interstriae) positioned between the striae make them appear broad in LM. When Lange-Bertalot (in Krammer & Lange-Bertalot 2004) erected Platessa he did not describe this interstriae feature as one of the characters of this genus, but several species have since been observed to have these kinds of ribs on the rapheless valve internally, such as Platessa lutheri , P. kingstonii and P. stewartii Potapova (2012: 38) . However, the rapheless valves are clearly ribbed between the cluster of internal areolae; this was described as a typical feature of the genus Planothidium ( Round & Bukhtiyarova 1996) .

Figures

FIGURES 1–6. Psammothidium hainanii sp. nov. Figs 1, 3, 5. Raphe valve. Figs 2, 4, 6. Rapheless valve. Figs 3, 4. Holotype specimen. Figs 7–16. Figs 7–16. Platessa guangzhouae sp. nov. Figs 7, 9, 11, 13, 15. Raphe valve. Figs 8, 10, 12, 14, 16. Rapheless valve. Figs 9,

FIGURES 17–22. Psammothidium hainanii sp. nov. Fig. 17. External view of raphe valve, scale bar = 10 μm. Fig.18. External view of the terminal fissure, scale bar = 3 μm. Fig. 19. External view of rapheless valve, scale bar = 10 μm. Fig. 20. Internal view of the raphe valve, showed the raised helictoglossae, scale bar = 2 μm. Fig. 21. Internal view of the rapheless valve, showed the raised sternum, scale bar = 4