The ciliary feeding mechanism of the Megathyridae (Brachiopoda), and the growth stages of the lophophore

Abstract

The Megathyridae Allan 1940 is a family of brachiopods in which the adult lophophore is of simple design, bilobed (schizolophous) in Argyrotheca and four-lobed (ptycholophous) inMegathyris. Little is known of feeding mechanisms in the family. H´erouard (1877), finding it difficult or impossible to observe the feeding currents of living brachiopods, constructed artificial lophophores of lead piping with fine perforations corresponding to the position of attachment of the filaments. Through these he forced water, while the artificial lophophores were immersed in a bowl of water. He assumed, wrongly, that the result would be similar to the action produced by cilia vibrating in water. His remarks on the working of an artificial lophophore resembling that ofMegathyris (=Argiope) were transcribed by Morgan (1883) without making it clear that the observations were not his own and were not made on the living animal. Apart from HÉerouard's work on artificial lophophores, the only reference to feeding in a member of the Megathyridae is that of Shipley (1883) who merely mentioned that inArgyrotheca the arrangement of the cilia is adapted to bring particles into the ciliated groove and thence to the mouth. Thus an examination of the method of feeding of the Megathyridae was considered desirable, and was made possible in the first instance through the kindness of M. Paul Bourgis, then, in 1955, on the staff of the Laboratoire Arago, Banyuls-surMer. He sent two small consignments of livingArgyrotheca cor data (Risso),A. cuneata (Risso) andMegathyris detruncata (Gmelin), received on the 28 October and 24 December 1955.