Amphora rhombica var. intermedia Cleve, 1895

Lobban, Christopher S., 2015, Benthic marine diatom flora of Guam: new records, redescription of Psammodictyon pustulatum n. comb., n. stat., and three new species (Colliculoamphora gabgabensis, Lauderia excentrica, and Rhoiconeis pagoensis), Micronesica 2015 (2), pp. 1-49 : 2

Amphora rhombica var. intermedia Cleve Figs 1–6

Ref. illus.: Peragallo & Peragallo 1897 –1908, pl. 50, fig. 3; Wachnicka & Gaiser 2007, fig. 118; Stidolph et al. 2012, pl. 24, fig. 70; Álvarez-Blanco & Blanco 2014, pl. 34, fig. 1.

Samples: GU43C

Dimensions: Length 62–110 µm, width 15–22 µm; dorsal and ventral striae 14–18 in 10 µm Diagnostics: Radiating striae of transapically elongate areolae; some central interstriae bifurcate toward the dorsal margin; no fascia; central area small; prominent conopeum both internally and externally. Dorsal margin slightly rhomboidal to uniformly curved, the ventral margin nearly straight to slightly arcuate, the raphe branches also nearly straight to slightly arcuate. Apices acute. Numerous copulae with areolae apparently on the pars interior not seen in external SEM view ( Fig. 6 ).

Comments: Differences similar to those shown in the two LM specimens ( Figs 1, 2 vs. 3, 4) can be seen in Peragallo & Peragallo’s (1897 –1908) drawings, one of which is identified as var. intermedia ; moreover, they noted differences from the original description of the nominate form, but chose not to erect another new variety. Further differences can be seen in size and striae counts of the Guam specimens and the range (for var. intermedia ) in Wachnicka & Geiser (2007); in particular our small specimens show no differences in stria density from center to apex nor between dorsal and ventral striae. The nominate variety is larger, distinctly semi-rhomboidal, has coarser striae (9–12 in 10 µm), and appears to lack the conopea (Schmidt et al. 1874–1959, pl. 40, fig. 39; Peragallo & Peragallo 1897 –1908, Wachnicka & Gaiser 2007). The very fine ventral striation (27 in 10 µm) on the specimen in Witkowski et al. (2000, pl. 168, fig. 12, 13) suggests yet another variety. A species in need of further study.

Common in a diatom coating on reef flat sand, very near low water, where it formed a community with A. decussata Grunow and an unidentified Amphora sp. among other genera.

Figures

Figs 1–6. Amphora rhombica var. intermedia (GU43C). Figs 1, 2. Valve with curved raphe at two focal planes (DIC). Figs. 3, 4. Valve with nearly straight raphe at two focal planes (DIC). Fig. 5. Internal view of valve showing conopeum over central raphe endings (SEM). Fig. 6. External ventral view of valve showing girdle bands and conopeum over the central raphe endings. Fig. 7. Asteromphalus cleveanus (GU52N-4) (DIC). Figs 8, 9. Asteromphalus hepactis internal view and detail (GU56A) (SEM). Scale bars: Figs 1–4, 6–8 = 10 µm, Figs 5, 9 = 5 µm.