Passive feeding in spiriferide brachiopods: an experimental approach using models of Devonian Paraspirifer and Cyrtospirifer

Abstract

Shiino, Y. 2009: Passive feeding in spiriferide brachiopods: an experimental approach using models of Devonian Paraspirifer and Cyrtospirifer. Lethaia, Vol. 43, pp. 223–231. Passive feeding flows of two Devonian spiriferide brachiopods, Paraspirifer bownockeri and Cyrtospirifer sp., were examined experimentally using transparent hollow models and a flowing water tank. The models were constructed with polycarbonate plates using a vacuum heat press method. Another model of Paraspirifer with a spiral brachidium was constructed for the visualization of passive flow. The results of the ventral and dorsal directions of the hollow models suggest that outflow was generated through lateral gapes in the shell, while intake may have occurred through a sulcus gape. The passive internal flow inside the models invariably exhibited gyrating behaviour, and the axis of the rotation was similar to that of the spiral lophophore in spiriferides. Comparing the results using the hollow and backbone models indicates that the internal structures, which consisted mostly of the spiral brachidium, aided in adjusting the gyrating flows around the brachidium, even when the lateral region of the shell faced upstream. Extant terebratulides are known to generate gyrating flows around the median coils of the major feeding area, and this model best fits the relationship between the passive internal flows and the form of the lophophore. As a consequence, the shell forms of spiriferides could generate passive feeding flows from the gyrating movement surrounding the lophophore that are effective for feeding by the spiral lophophore. □Brachiopoda, flume experiment, functional morphology, impingement feeder, physiology, suspension feeder.