Actinellopsis giraffensis (Siver, A.P. Wolfe & Edlund) J.C. Taylor, B. Karthick & Kociolek

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 : 134-135

Actinellopsis giraffensis (Siver, A.P. Wolfe & Edlund) J.C. Taylor, B. Karthick & Kociolek , comb. nov.

Basionym: Actinella giraffensis Siver et al. (2010: 343 , figs 1A–I, figs 2A–F, figs 3A–F).

Actinellopsis superficially resembles Actinella , which is also cuneate and asymmetrical about the transapical axis. The two differ in the type of raphe system and that Actinella is also asymmetrical about the apical and transapical axes. The superficial similarities in symmetry are due to independent acquisition of asymmetry about both the transapical and apical axes. Valve symmetry and other frustule organization (amphoroid organization) appear to have evolved independently many times (e.g. Cox 1979, Medlin 1991, Medlin & Round 1986, for Eunophora Vyverman, Sabbe &

D.G. Mann in Vyverman et al. 1998: 96; Stepanek & Kociolek 2014). Table 1 compares features of Actinellopsis with Eunotia , Peronia and Actinella .

from Round et al. 1990).

Actinellopsis murphyi differs from A. giraffensis in the outline of the valve, having a more protracted ‘headpole’ as seen in valve view.

The disjunct distribution between Actinellopsis murphyi from Zambia and the 50 million year old fossil Actinellopsis giraffensis from the Canadian Arctic is puzzling. The Zambian locality is subtropical and an acid habitat (pH 6.5). The Canadian Arctic of the Eocene was quite different from today, with many subtropical to tropical species known from fossil localities ( Eberle & Greenwood 2012). Freshwater fossil deposits of Eocene age are relatively rare (e.g. Benson et al. 2012), thus the temporal and spatial extent of Actinellopsis is not well understood. It is possible that the genus was much more widely distributed, and the species from Zambia represents a relict. Alternatively, an African-South American connection may have existed (as has been documented for many taxa, see Renner 2004 for a compilation of plant species), followed by a north-south connection in the new world between South and North America.

This genus appears to be an example of a Lazarus taxon, where a taxon occurs in the fossil record, there is a gap in its occurrence, and it “reappears” again ( Jablonski 1986). Such taxa are known in plants (e.g. Chaney 1948), invertebrates (Fraiser & Bottjer 2005; Skelton & Gilli 2012) and vertebrates ( Friedman & Coates 2006; Dawson et al. 2006). They are the result of observational gaps, due to sampling or loss via the fossilization process.