. Bulletin of the British Museum (Natural History), Geology. CHONETACEAN BRACHIOPODS 5 leads to the opinion that the lophophore in these fossil groups consisted of a schizolophe or variously lobed forms of a ptycholophe. In the sense of Williams & Rowell {in Williams et al 1965 : H37-8) it is a lobed trocholophe because the lophophore is believed to have had only a single series of filaments, as in Recent Thecidellina, rather than the more complex double filaments characteristic of most other Recent lophophores from the schizolophous to plectolophous stages. Rudwick (1968) reminds us that
. Bulletin of the British Museum (Natural History), Geology. CHONETACEAN BRACHIOPODS 5 leads to the opinion that the lophophore in these fossil groups consisted of a schizolophe or variously lobed forms of a ptycholophe. In the sense of Williams & Rowell {in Williams et al 1965 : H37-8) it is a lobed trocholophe because the lophophore is believed to have had only a single series of filaments, as in Recent Thecidellina, rather than the more complex double filaments characteristic of most other Recent lophophores from the schizolophous to plectolophous stages. Rudwick (1968) reminds us that the terminology employed to describe lophophores was based originally upon the arrangement of the brachial axis without consideration for the number of filament rows. Thus whilst phylogenetically there is logic in Williams and Rowell's terminology (1965, H38), it is less confusing to retain the previously existing definitions qualified, where necessary, to indicate if the filament series is double or single. Believing that the thecideaceans may be remnants of the Strophomenida, derived from a productidinid stock not far removed from Cooperina Termier, Termier & Pajaud 1967 (but see Cooper & Grant 1969), it is logical to interpret the chonetacean lophophore as having been only a single row of filaments (Text-fig. i). In his study of the Triassic brachiopods Thecospira and Badryniiim ,did ^ . — P'lG. I. Diagrammatic dorsal valve interior of a chonetacean showing, on the left, general morphology and, on the right, the inferred anatomy and suggested water currents associated with the lophophore, a. - anderidium; - anterior adductor muscle scar; — adductor muscle, ventral attachment area; - brachial platform; - inner epithelium of the body wall separating the brachial cavity from the visceral cavity. The epithelium of the visceral cavity has been cut ventro-medianly to expose the muscles; did. - diductor muscle; - v
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