Catenulaceaea Mereschkowsky

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 : 31-33

Family Catenulaceaea Mereschkowsky

Amphora acutiuscula Kützing (Pl. 8, Fig. 9) References: Krammer & Lange-Bertalot 1986, p.348, fig. 151:6; Snoeijs & Potapova 1995, p. 21, fig. 209; Witkowski et al. 2000, p. 128, pl. 161, figs 10-13.

Features: Apical axis 34-50 µm, transapical axis: 7-11, striae 16-20 in 10 µm.Valves broadly semi linear-lanceolate with produced sub-capitate apices. Raphe close to the ventral margin. Striae on the dorsal side radiate.

Remarks: The observed specimens characterized by broad valves. Images shown in Witkowski et al. (2000) have much narrower valves than the dimensions given in their text (ref. cit., p. 128). Snoeijs & Potapova (1995) reported valves with width not exceeding 7 µm.Widely distributed species in marine and brackish water.

Occurrence: Rare in Reunion and Rodrigues Islands.

Amphora bigibba Grunow (Pl. 13, Figs 1 , 2) References: A. Schmidt Atlas, pl. 25, figs 66, 67, 69-77; Hustedt 1955, p. 40, pl. 14, figs 19-25 (as Amphora binodis var. bigibba (Grunow) Peragallo ); Navarro 1982, p. 322, fig. 17; Navarro & Lobban 2009, Figs 135, 136.

Features: Apical axis: 18-22 µm, transapical axis: 4-6 µm, striae 25-27 in 10 µm on the dorsal side, 35-38 in 10 µm on the ventral side. Valves lanceolate, constricted at the middle forming two convex sides, with truncate sub-acute apices. Raphe straight and close to the ventral margin. Occurrence: Rare in Reunion Island. Previously reported from Seychelles (G).

Amphora coffeaeformis (C.Agardh) Kützing (Pl. 8, Figs 4, 5) References: Krammer & Lange-Bertalot 1986, fig. 151:1-6; Witkowski et al. 2000, pl. 161, figs 21- 25.

Features: Apical axis: 32-40 µm, transapical axis: 8-12 µm, striae 12-20 in 10 µm. Valves linear to elliptic-lanceolate, arcuate on the dorsal side, with produced capitate apices. Raphe very close to the ventral margin which is slightly concave in some specimens.

Remarks: Stria density in the observed specimens are less than that reported for the species (see ref. cit.). Under LM, this species may look similar to Amphora acutiuscula Kützing but the latter possess a higher stria density. Widespread species in coastal regions and in inland waters with high conductivity.

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

Amphora helenensis Giffen (Pl. 13, Figs 5, 6) References: Giffen 1973, p. 33, figs 7-9; Witkowski et al. 2000, p. 139, pl. 163, figs 31-33. Features: Apical axis: 6-8 µm, transapical axis: 3-4 µm, striae 24-25 in 10 µm. Valves lunateshaped with broadly round apices. Raphe close to the ventral margin, slightly bi-arcuate. Axial area narrow, central area extend to one direction. Striae composed of transverse areolae.

Remarks: Stria density rather higher than that reported by Wikowski et al. (2000). Observed specimens were with small valves which could not be clearly resolved under LM.

Occurrence: Rare in Reunion Island.

Amphora holsatica Hustedt (Pl. 8, Figs 2, 3) References: Krammer & Lange-Bertalot 1986, p. 349, fig. 152:1-6; Simonsen 1987, pl. 132, figs 11-16.

Features: Apical axis: 30-45 µm, transapical axis: 8-12 µm, striae 10-14 in 10 µm. Valves semi-lanceolate with protracted sub-subrostrate apices. Dorsal margin convex, ventral margin flat to slightly concave. Raphe straight, fifliform, very close to ventral margin. Striae on dorsal margin coarsely punctate and very fine on ventral margin.

Remarks: Under LM, this species looks very similar to A. pseudoholsatica Nagumo & Kobayasi , A. holsaticoides Nagumo & Kobayasi and A. subholsatica Krammer. Stria density on the dorsal side of the valve appears similar in all of these taxa. The main differences are in the ultrastructure of some features other than stria density which can only be observed under SEM.

Occurrence: Frequent in Reunion and rare in Rodrigues Island.

Amphora laevissima W. Gregory (Pl. 8, Fig. 1 ) References: Snoeijs & Balashova 1998, p.22, fig. 410; Witkowski et al. 2000, p. 142, pl. 168, figs 5-7.

Features: Apical axis: 42-60 µm, transapical axis: 8-12 µm, striae 26-28 in 10 µm on the dorsal side. Valves linear lanceolate, slightly constricted in the middle of ventral side, with slightly deflected sub-truncate apices. Raphe bi-arcuate, axial area very narrow, central area dilated to a sort of fascia reaching the dorsal valve margin.

Remarks: This is a common species found in all marine environments.

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

Amphora cf. marina W. Smith (Pl. 8, Figs 6, 10) References: Witkowski et al. 2000, pl. 162, figs 8-14, pl. 166, figs 9-11; Al-Handal & Wulff 2008, p. 54, figs 112-115; Levkov 2009, p. 470, Fig. 7.

Features: Apical axis: 16-28 µm, transapical axis: 6-8 µm, striae 14-16 in 10 µm.

Remarks: Only small specimens were observed which match the illustrations of A. marina . The ventral striae which is composed of single, clearly elongated areolae increased in length towards the mid-valve and converge toward the ends may distinguish this species. Widely distributed species on marine coasts.

Occurrence: Frequent in Reunion, rare in Rodrigues Island.

Amphora pediculus (Kützing) Grunow (Pl. 13, Fig. 3) References: Krammer & Lange-Bertalot 1986, fig.150: 8-13; Snoeijs 1993, p. 24, fig. 10.

Features: Apical axis: 3-6 µm, transapical axis: 4-5 µm, striae 20-22 in 10 µm. Valves broadly semi-elliptic with arched dorsal margin and round apices. Raphe straight, distal raphe endings dorsally deflected. Dorsal striae with 2-3 rows of areolae and ventral striae composed of one row of areolae.

Remarks: Very small species, striae not resolved under LM. Freshwater species, most likely drifted to the study sites.

Occurrence: Rare in Rodrigues Island.

Amphora cf. rhombica var. intermedia Cleve (Pl. 13, Fig. 4) References: Peragallo 1897 -1908, pl. 50, fig. 3; Snoeijs & Kasperoviciene 1996, p. 28, fig. 316. Features: Apical axis: 45 µm, transapical axis: 7-9 µm, striae on the dorsal side 13-15 in 10 µm, 15-18 in 10 µm on the ventral side. Valves semi-rhomboidal with slightly inflated ventral margin and convex dorsal margin. Raphe slightly bi-arcuate, central area small, axial area narrow. Dorsal striae composed of rows of elongated areolae.

Remarks: The observed specimens were relatively small. This taxon differs from the nominate variety only by its valve size and coarser striae. A fresh to brackish water species, probably drifted to the study site.

Occurrence: Rare in Rodrigues Island. Previously reported from Seychelles (G).

Halamphora angularis (Greory) Levkov (Pl. 14, Fig. 2) References: Levkov 2009: p. 169, pl. 110, fig. 16, pl. 250, figs 5, 6

Features: Apical axis: 26-28 µm, transapical axis: 6-8 µm, striae 17-19 in 10 µm.

Occurrence: Rare In Reunion Island.

Figures

Figure 1. Map showing location of Reunion and Rodrigues Islands, Indian Ocean and sampling sites.