Liljevallia gotlandica: encrustation patterns in the earliest cemented articulate brachiopod, and their implications for its larval behaviour

Abstract

Examination of c. 100 specimens of the encrusting brachiopod Liljevallia gotlandica Hedström reveals: (a) that it was a cryptic form, cementing its ventral valve to the roofs of reef caverns and subskeletal cavities or overhangs; (b) that its larvae were gregarious, favouring sites occupied by living or dead conspecifics; (c) that its orientation (determined by the larva) was predominantly with the commissure facing downslope. The operation of positive geotropism during late larval life is suggested. The hypothesis known as “slopelet line docking”, originated by Struve (1980) for Devonian cryptic encrusters in subskeletal cavities, is neither supported nor contradicted by Liljevallia. In a survey of other encrusting brachiopods, downslope orientation of the commissure is revealed to be a widely adopted stratagem, and the reasons for this are examined in the light of recent findings.