Morphology and function of the perforation (keyhole) in Pygopidae (Terebratulida, Brachiopoda)

Abstract

For examination of their internal features, 14 specimens of Pygope and Antinomia from the Bakony Mts. were sectioned longitudinally and transversely. The perforation of the dorsal valve continues in a long tube which joins a short collar of the ventral valve. In slightly opened shells a narrow gap appears between the collar and the tube. The posterior part of the gap is near the rim of the ventral collar. In the new model of the feeding mechanism of pygopides this feature involves that the exhalant jet passed directly over the ventral entrance of the tube. The propulsion of the exhalant jet might generate a low-pressure regime in the tube. An advantage of this process is increasing circulation through the mantle cavities of the lateral lobes, by the sucking effect of the low-pressure regime. The pygopide might lift itself from the mud by contracting the adjustor muscles of its pedicle. The underlying unconsolidated mud is stirred up and the fine grained organic-rich material may be sucked into the low-pressure area of the tube. Then this suspended matter might be ejected off the tube and the food might be recycled by the inhalant currents. With 14 figures and one table.