The Early Cambrian tommotiid Micrina, a sessile bivalved stem group brachiopod

Mitral and sellate Micrina sclerites can be reconstructed as a near-bilaterally symmetrical sessile bivalved organism: sellate sclerites preserve paired muscle scars, while mitral apophyses are interpreted as muscle platforms. Valve homology and stem-brachiopod placement remain hypotheses rather than preserved articulation.

The Brachiopoda root display replaces the legacy 540 Ma bound with a rounded 520–0 Ma total-group navigation envelope anchored by Early Cambrian Micrina sclerites reconstructed as a stem brachiopod; it is not a crown-brachiopod FAD.

Isolated Micrina sellate sclerites with paired muscle scars and mitral apophyses interpreted as muscle platforms support a reconstructed bivalved body and stem-brachiopod model; articulation, valve homology and direct ancestry are not preserved.

The brachiopod-origin dossier is a navigation route joining Micrina and Yuganotheca character tests; it is not a taxon, direct-ancestor sequence or global brachiopod first-appearance claim.

Micrina material from four localities in three broadly synchronous late Atdabanian carbonate units supports a conservative Cambrian Stage 3 study-sample envelope of 521–514.5 Ma, not a global genus range, a brachiopod origin date or a direct-ancestor sequence.

Micrina is retained as a tommotiid genus represented by isolated mitral and sellate sclerites; sellate paired muscle scars and mitral apophyses interpreted as muscle platforms inform a reconstructed bivalved arrangement, while valve homology and phylogenetic placement remain comparative hypotheses rather than preserved articulation.

The represented Micrina material includes the Lower Cambrian Wilkawillina Limestone of the Arrowie Basin, South Australia, among four localities in three broadly synchronous carbonate units; these named collections do not establish a complete geographic distribution or an origin centre.

The reconstructed Micrina body is interpreted as sessile in an Early Cambrian marine carbonate setting, but diet, locomotion, guild and whole-body dimensions are not directly preserved by the isolated sclerites.

Micrina sellate phosphatic sclerites preserve paired muscle scars, whereas mitral sclerites bear apophyses interpreted as muscle platforms; their near-bilateral bivalved assembly is a reconstruction, not a fossil preserving both articulated valves.