Pyrgodiscus Kitton ex Cleve 1885: 173

Williams, David M. & Sims, Pat A., 2023, Notes on the diatom collection of the Natural History Museum, London (BM) VII: An account of some original specimens of Pyrgodiscus (Bacillariophyta) with notes on Stephanogonia (Bacillariophyta), Phytotaxa 589 (3), pp. 213-229 : 217

Pyrgodiscus Kitton ex Cleve 1885: 173

Pyrgodiscus F.Kitton ex P.T. Cleve, 1885 in GBIF Secretariat (2021), GBIF Backbone Taxonomy. Checklist dataset GBIF Secretariat (2021, accessed via GBIF.org on 2021-12-22; also De Toni 1894: 1011 [no. 4239]).

TYPE:— Pyrgodiscus armatus Kitton ex Cleve 1885

MATERIAL: BM (summarised in Natural History Museum 2021); descriptions in De Toni (1894: 1011), Van Heurck (1896: 426) and Taylor (1929: 215).

Valves circular, with central dome or pillar. Surface surrounding pillar areolate with evenly spaced stout spines that taper towards their tips. Similar series of spines surrounding surface of pillar, stouter than those on lower part of valve, but not equal in length.

The twin series of independent spines are a (proposed) synapomorphy of the genus.

Possibly a resting spore (e.g., Chambers 1997: 344), since its first description the genus Pyrgodiscus acquired only a few additional species, some having since been transferred to more appropriate genera, others identified as synonyms of species in genera different to Pyrgodiscus , and a few awaiting further investigation ( Table 2 ; it is of note that half of the species in Pyrgodiscus were described relatively recently by Hajós & Stradner from Late Cretaceous DSDP material [ Hajós & Stradner 1975], none of which should remain in Pyrgodiscus , see below for summary). In spite of these additions, only Pyrgodiscus armatus and P. simplex should remain in the genus, although electron microscopy may inform otherwise.