Actinellopsis murphyi J.C. Taylor, B. Karthick & Kociolek, 2014

Taylor, Jonathan C., Karthick, Balasubramanian, Kociolek, J. Patrick, Wetzel, Carlos E. & Cocquyt, Christine, 2014, Actinellopsis murphyi gen. et spec. nov.: A new small celled freshwater diatom (Bacillariophyta, Eunotiales) from Zambia, Phytotaxa 178 (2), pp. 128-137 : 132-134

Actinellopsis murphyi J.C. Taylor, B. Karthick & Kociolek spec. nov. ( Figs 1 –45)

Type:— ZAMBIA, Luapula Province, Ntumbachushi Falls on Ngona River near the town of Kawambwa , (09.853736°S, 28.944683°E). Sample collected by J.C. Taylor from detrital material on rocks wetted by seeping water from spray zone of main falls. Slide BR 4375, Botanic Garden Meise, holotype designated here (the valve representing the holotype is here illustrated as Figure 12 ); D- NWU 12-349 , South African National Diatom Collection , isotype designated here .

Cells clavate in girdle view 15.5–23.0 μm long. Plastid structure unknown. Valves weakly clavate and dorsiventral with ventral margin straight to slightly convex and dorsal margin convex, 2.2–3.1 μm wide at widest point of valve. Head pole subcapitate, foot pole not tumescent. Striae rather difficult to resolve in LM, 28–30 in 10 μm, parallel in the centre of the valve becoming radiate towards the apices. Areolae round, occluded by vela. No marginal spines. One valve possessing a short and arched raphe, the other valve possessing a longer, straight raphe. Distal and proximal ends slightly rounded but otherwise unmodified and situated at the junction of valve face and mantle. Helictoglossae indistinct. Rimoportula on headpole and footpole, orientated parallel to apical axis. Cingulum composed of 4 open, porous copulae.

Etymology:— The specific epithet refers to the project co-coordinator of the SAFRASS project, Dr. Kevin Murphy of the University of Glasgow and is named after him to honour his contributions to the extension of the knowledge of the Zambian fauna and flora.

Distribution and ecology:— Actinellopsis murphyi has been found only from the type locality. It is found rarely in a sample that was collected from detrital material in seeping water flowing over the stones comprising the steps of a foot path next to the main cataract of Ntumbachushi Falls. The path was heavily shaded and covered in leaf litter. The seep water had its origin in the spray from the main falls, the permanency of this seep is uncertain. The main stream of the falls had the following characteristics pH 6.56, 18.13°C, 4 μS cm-1 electrical conductivity and oxygen concentration of 9.70 mg l-1.

Observations:— Actinellopsis murphyi is a small taxon distinguished from other similar species by its distinct valve shape and size, the shape of the head pole and the striae density. It is comparable to the fossil species Actinella giraffensis Siver, A.P. Wolfe & Edlund ( Siver et al. 2010: 343), being similar in valve symmetry (dorsiventral and heteropolar with an almost straight ventral valve margin). It also has epi and hypovalves with longer and shorter raphe slits. It appears that the epivalve of Actinellopsis murphyi bears the longer raphe ( Fig. 24 ) and the hypovalve the shorter more strongly curved raphe (a characteristic somewhat similar to Peronia ). Actinellopsis murphyi differs from Actinella giraffensis in regard to striae density and the shape of the headpole. These two species are very similar in girdle view and the positioning of the raphe slits at the valve margin is almost identical. It is also comparable to Actinella indistincta Vyverman & E.A. Bergey (in Sabbe et al. 2001: 328), the striae density is similar but the outline of the cell (arcuate) and structure of the apices is very different. In addition the raphe is almost entirely situated in the mantle and the cells are isovalvar.

Actinella disjuncta Metzeltin & Lange-Bertalot (2007: 28) is another species with a similar valve outline was described from a fossil samples of Brazilian Amazon (Lago Calado) and from a cataract in Sarawako Bako (Borneo, Malaysia). Actinella disjuncta , however, shows conspicuous spines, a raphe canal located on the valve mantle and coarser interstriae with the areolae placed deeply in the valve face (see Metzeltin & Lange-Bertalot 2007, pl. 41: figs 1–24 and pl. 42 figs 1–7).

Figures

FIGURES 1–20. LM images of Actinellopsis murphyi gen. et. spec. nov., valves from holotype D-NWU 12-349, Ntumbachushi Falls on Ngona River, in Zambia, showing the size range in valve view. Figs 1–16. Valve view. Figs 17–20. Girdle view. Scale bar = 10 µm.

FIGURES 21–25. SEM images of valve exterior of Actinellopsis murphyi gen.et spec. nov. Figs 21–23. SEM images showing the external valve view. Fig. 24. SEM image of external girdle view showing epi and hypovalves with longer (L) and shorter (S) raphe slits External rimoportulae (R) opening indicated. Fig. 25. SEM image of the external girdle view of dorsal margin. Scale bar = 5 µm (21, 22, 23), 2 µm (24, 25).