Micrhystridium hamatum (Downie, 1958) Deflandre and Deflandre-Rigaud, 1965

Now Baltisphaeridium hamatum (an acritarch species). Originally Hystrichosphaeridium hirsutoides var. hamatum, subsequently Baltisphaeridium hirsutoides var. hamatum (an acritarch varietas), thirdly Micrhystridium hamatum,
fourthly Acanthodiacrodium hamatum (an acritarch species) fifthly (and now) Baltisphaeridium hamatum (an acritarch species). Thus taxon was raised to specific rank by Deflandre and Deflandre-Rigaud, 1965 as Micrhystridium hamatum.
Holotype: Downie, 1958, pl.16, fig.1
Age: Early Ordovician