Temporal range: Late Llandovery – ?Late Lochkovian
|A restoration of Birkenia elegans (middle) compared with three Ainiktozoon loganese|
| †Birkenia elegans|
Intact fossil specimens of B. elegans suggest the living animal reached a length of up to 10.0 cm (3.9 in), and was an active swimmer. In addition to whole specimens and scale microfossils of B. elegans, which are found in Great Britain and Scandinavia, scales of a second species, B. robusta, are found in Late Silurian strata of Scandinavia and Estonia. The scales of B. robusta differ from those of B. elegans in that, as the specific epithet suggests, the scales of the former are more robustly proportioned than those of the latter.