Distribution and orientation of six articulate brachiopod species from New Zealand

Abstract

Neothyris lentieularis, Terebratella sanguinea, and T. ineonspicua occur as both attached and free-lying populations; Liothyrella neozelaniea and Nolosaria nigrieans assume the attached habilt only. Attached individuals of these: five species examined in situ were consistently oriented with the dDrsail valve next to, the substralte; preferred orientations to other axes (right-left and anterior-posterior) were not evident. Free-lying individuals of T. ineonspicua and T. sanguinea were randomly oriented wi1th regard to both axes, but free-lying N. lenticularis showed a preference for lying on the dorsal valve. The position of N. lenticularis relative to the anterior-posterior axis Couid apparently be influenced by the strength of water currents. Neothyris compressa was not observed in situ, but free-lying individuals in an aquarium oriented actively to strong currents. Use of the terms ‘free-lying’ and ‘attached’,is examined in rellation to fossil and living popuhlltions.