Bacillaria paxillifera var. tumidula (Grunow) Witkowski, Lange-Bertalot & Metzeltin

Al-Handal, Adil Y., Compère, Pierre & Criobe-Usr, Catherine Riaux-Gobin, 2016, Marine benthic diatoms in the coral reefs of Reunion and Rodrigues Islands, West Indian Ocean, Micronesica 2016 (3), pp. 1-78 : 34-35

Bacillaria paxillifera var. tumidula (Grunow) Witkowski, Lange-Bertalot & Metzeltin

(Pl. 10, Fig. 3)

References: Hustedt 1931 -59, p. 849, fig. 756; Wikowski et al. 2000, p. 357, pl. 196, fig. 8.

Features: Apical axis: 80-110 µm, transapical axis: 6-9 µm, striae 24-26 in 10 µm, fibulae 10-12 in 10 µm. Valves linear lanceolate with produced apices and inflated sides in the central part. Keel occupy central position on valve face with unevenly spaced fibulae.

Remarks: Easily distinguished from the type variety by the inflated central part of the valve which do not appear identical on both sides of the median line.

Occurrence: Frequent in Reunion and rare in Rodrigues Island.

Bacillaria socialis (Gregory) Ralfs (Pl. 10, Fig. 8) References: Poulin et al. 1990, p. 75, figs 2-4, 8; Witkowski et al. 2000, p. 357, pl. 196, figs 5-7, pl. 207, fig. 9.

Features: Apical axis: 36-50 µm, transapical axis: 5-7 µm, fibulae 9-10 in 10 µm. Valves linear lanceolate tapering into produced subacute apices. Keel central, fibulae evenly spaces.

Remarks: According to Jahn & Schmidt (2007), both Bacillaria paxillifera var. tumidula and B. socialis do not belong to the genus Bacillaria Grunow. These authors compared the Grunow’s and Gregory’s ( Nitzschia socialis ) lectotypes with Witkowski et al. (2000) images and found noticeable differences in valve structure. In this context, these taxa needs to be examined thoroughly under LM and SEM and to compare them with lectotypes to verify their correct identity.

Occurrence: Rare in Reunion and Rodrigues Islands. Previously reported from Seychelles (G).

Ceratoneis closterium Ehrenberg (Pl. 10, Fig. 9) References: Krammer & Lange-Bertalot 1988, p. 124, fig. 87:1, 2; Witkowski et al. 2000, p. 374, pl. 212, figs 4-6 (both as Nitzschia closterium (Ehrenberg) W. Smith ); Jahn & Kusber 2005, p. 301, figs 3-7.

Features: Apical axis 40-210 µm, transapical axis 3-6 µm, striae very fine, fibulae 30-36. Valves narrowly elliptical tapering into long hair-like apices, usually deflected either to the same or to opposite directions. Raphe eccentric. Fibulae evenly spaced but the central two are more distant. Remarks: This species is often identified as Cylindrotheca closterium (Ehrenberg) Reimann & Lewin. The genus Ceratoneis Ehrenberg has been typified by Jahn & Kusber (2005) and included species of the genus previously classified under Nitzschia and Cylindrotheca . Widespread species in all marine and brackish waters.

Occurrence: Common in Reunion and Rodrigues Islands. Previously reported from Seychelles (G).

Nitzschia distans Gregory (Pl. 10, Fig. 12) References: Hendey, 1964, p. 281; Witkowski et al., 2000: p. 378; pl. 203, figs 7-9.

Features: Apical axis: 40-52 µm, transapical axis: 4-7 µm, striae very fine, fibulae unevenly spaced, 3-5 in 10 µm. Valves narrow lanceolate with produced apices having short braod extensions seen only in girdle view. Keel central, fibulae irregular in size. Striae interrupted by a longitudinal line on both sides of the keel.

Remarks: Striae in the observed specimens could not be resolved under LM but the species can be distinguished by the inflated corners with the short expansions in the girdle view.

Occurrence: Rare in Reunion island. Previously reported from Seychelles (G).

Nitzschia hybrida Grunow (Pl. 10, Fig. 10) References: Krammer & Lange-Bertalot 1988, p. 61, pl. 46, figs 3-6; Witkowski et al. 2000, p. 385, pl. 191, figs 12-14.

Features: Apical axis: 55 µm, transapical axis: 8 µm, striae 28 in 10 µm, fibulae 8 in 10 µm. Vaves linear, slightly constricted in mid-part of dorsal margin, with acutely round apices. Raphe eccentric, fibulae unevenly spaced, the two central ones are distant.

Remarks: A single specimen was observed which is relatively small for this species. A widely distributed species particularly in brackish waters, rarely from tropical waters.

Occurrence: Very rare in Reunion Island.

Nitzschia insignis Gregory (Pl. 10, Fig. 11) Reference: Witkowski et al. 2000, p. 387, pl. 202, fig. 5, pl. 204, figs 1-7.

Features: Apical axis: 72 µm, transapical axis: 7 µm, striae 12-14 in 10 µm, fibulae 6 in 10 µm. Valves linear with round apices. Raphe central, fibulae elongated and occupying almost half of the valve width.

Remarks: Only two specimens were observed, valve size rather small.

Occurrence: Very rare in Rodrigues Island.