Orthoseira papuensis Kochman-Kedziora & Van de Vijver, 2024

Kochman-Kedziora, Natalia & Van de Vijver, Bart, 2024, The genus Orthoseira (Orthoseiraceae, Bacillariophyta) in Papua New Guinea with the description of two new species, Plant Ecology and Evolution 157 (2), pp. 113-124 : 113

Orthoseira papuensis Kochman-Kedziora & Van de Vijver sp. nov.

Fig. 4

Type locality.

Boisa Island, Papua New Guinea, sample 158, 4°00 ’00” S, 144°57 ’30” E, elev. 20 m a.s.l., 30 Dec. 1989, leg. R. Iserentant.

Type.

Boisa Island , Papua New Guinea , sample 158; holotype: slide BR-4818, BR; the valve representing the type is illustrated here in Fig. 4F ; isotype: slide 434, University of Antwerp , Belgium .

Registration.

http://phycobank.org/104293

LM description.

Frustules cylindrical in girdle view, connected to each other forming short chains (Fig. 4G, H ). Valves disc-shaped. Valve dimensions (n = 20): valve diameter 6.5-23.0 μm, mantle height 8.0-9.5 µm. Valve face flat, sloping abruptly at the valve face/mantle junction, visible in LM as a darker circular edge. Central area small, maximum 1/4 of the total valve diameter, irregular in shape. Three to four large, rounded carinoportulae present. Between the carinoportulae scattered areolae present. Striae on the mantle long, uniseriate, 22-24 in 10 μm. Valve face areolae rather small, arranged in radiate, uniseriate striae, 16-22 in 10 µm. Caverns, internal undulations or internal valves not observed. Figure 4A-H .

SEM description.

Valve face flat, striae radial composed of round rimmed areolae (Fig. 4L ). Near the valve edge, areolae slightly larger (Fig. 4I-K ). Irregular pattern of small siliceous curving ridges, of variable length and shape, present over the entire valve face, including between the carinoportulae. Several (3-4) carinoportulae in the central area, surrounded by irregular siliceous circular ridges (Fig. 4J, L ), often obscured by plate-like coverings (Fig. 4I, K ). Small acute spines irregularly scattered along the valve face/mantle junction, occasionally absent (Fig. 4I, K, M ). Mantle very deep composed of two parts, advalvar with areolae organised in parallel, uniseriate series, 22-24 in 10 µm, located between weakly raised ridges. Ridges flattering in the middle of the mantle, followed by a hyaline, non-perforated abvalvar part (Fig. 4M, O ). Internally areolae occluded with individually hymenate vela (Fig. 4N ). Carinoportulae pit-like, formed by large rounded foramina, filled with siliceous plug (Fig. 4N ). Between the carinoportulae, three long slits present (Fig. 4N ), arranged in a star-shaped manner. Internal caverns not observed. Cingulum composed of broad, open, ligulate girdle bands, perforated with a large number of scattered poroids, irregularly organised in parallel series (Fig. 4M, O ). Figure 4I-O .

Etymology.

The specific epithet " Orthoseira papuensis " refers to the geographic locality where the new species was found.

Ecology and associated diatom species

All samples used in this study were collected from terrestrial mosses with a varying degree of moisture content. Sample 17 was taken from wet Hypnum mosses on trunks of several Ericaceae bushes. Water squeezed out of the mosses had a pH of 5.4. The sample, used for the description of O. iserentantii , is dominated by several Eunotia species with the most abundant one showing a high similarity to E. sphagnicola Van de Vijver, A.Mertens & Lange-Bert., Stauroneis obtusa Lagerst., and Humidophila cf. potapovae R.L.Lowe, Kociolek & Q.You. This diatom flora, although rather species-poor, is commonly found in wet acidic terrestrial mosses. The second sample in this study, sample 110, was collected on Karkar Island, a small (total area 360 km2) island in the Bismarck Sea, close to the coast of Papua New Guinea. The diatom composition in the sample is rather species poor and contains almost exclusively species from the genera Humidophila (mainly H. paracontenta var. magisconcava (Lange-Bert.) R.L.Lowe, Kociolek, J.R.Johans., Van de Vijver, Lange-Bert. & Kopalová), Luticola ( L. cf. isabellae Metzeltin & Levkov and L. acidoclinata Lange-Bert.), Pinnularia (mainly an unknown species from the P. borealis Ehrenb. group), and Hantzschia (such as H. amphioxys (Ehrenb.) Grunow in Cleve and Grunow 1880). These genera are very typical in dry to moist, terrestrial (= aerophytic) environments ( Lange-Bertalot et al. 2017). Samples 156 and 158 were collected on a second Papuan island, Boisa Island, a very small (total area 1.29 km2), flattened volcanic islet located not far from Karkar Island. Both samples contain large populations of several Humidophila species ( H. paracontenta var. magisconcava in sample 156, H. cf. potapovae in sample 158), Luticola (mainly L. acidoclinata but also L. hustedtii Levkov, Metzeltin & A.Pavlov), Hantzschia cf. amphioxys , and Pinnularia ( Pinnularia borealis -group). Sample 156 is dominated by Orthoseira tropica , whereas sample 158 is characterised by a larger population of O. papuensis . Given the subtle difference in sample description between both samples (156 from slightly wet mosses, 158 from rather dry mosses), this may indicate that O. tropica prefers wetter (or at least more moist) conditions and O. papuensis is mainly found in drier circumstances. More samples will have to be analysed to determine the exact ecological preferences of each species.

Figures

Figure 4. Orthoseira papuensis Kochman-Kedziora & Van de Vijver sp. nov. LM (A-H) and SEM (I-O) pictures taken from the holotype material (BR- 4818, sample 158, Boisa Island, Papua New Guinea). A - F. LM pictures of valves in valve face view. G - H. Frustules in girdle view. I - K. SEM external view of a valve face. L. SEM external detail of central part of the valve face with carinoportulae. M, O. Valves in girdle view with perforated girdle bands. N. Internal view of a complete valve. Scale bars: A-K, M-O = 10 µm; L = 5 µm.