ABSTRACT
The embryonic shells (protegula) of Early and Late Devonian linguloid brachiopods from Poland and Podolia display distinct differences in embryonic shell development as compared to extant lingulid relatives. Devonian protegula are cup-shaped subcircular structures, that range in width from 81 to 100 m in the Late Devonian, and from 76 to 95 m for the Early Devonian specimens. Protegula of Recent Lingula are at least three times larger than those of Devonian linguloids. The Devonian protegula are characterised by distinctive microtopographic structures including a central depression, radial ribs, hemispherical pits, tubercles, and rheomorphic deformations including nick points and drapes. Their subcircular outline suggests that dorsal and ventral protegula were secreted independently by separate dorsal and ventral secretional areas (mantle lobes). In contrast, the protegulum of Recent lingulids is initially a single double-folded plate.
