Functional disposition of the lophophore in living Brachiopoda

Emig, C. C. 1992 07 15: Functional disposition of the lophophore in living Brachiopoda. The shape and disposition of adult brachiopod lophophores relate to in- and excurrent apertures. to the internal water irrigation system, to shell orientation at substratum and to near-bottom currents. The arrangement of the mantle canals and gonads of different lophophores are induccd by water circulation. The trocholophe (2% of living species) is considered as a plesiomorphic character which represents the basic plan of the lophophore, shared by all Lophophorata. Three different types of schizolophe (10%) are represented in terebratuloids, thecidioids and discinids. The spirolophe (19%), characteristic of rhynchonellides and most inarticulate brachiopods, except the schizolophe Pelagodiscus, has evolved divergently into specific arrangements of the mantle canals and gonads. The zygo-plectolophe (67%) is characteristic of most Terebratulida. The ptycholophe (2%) probably evolved independently in Megathlris and the thecidioids. The mesolophe, known in the fossil chonetdceans, is considered to be a primitive zygo-plectolophe. The median brachiopod sulcus increases the efficiency of the excurrent system and is considered as an evolved character but a homoplasy within the brachiopods. The characteristics of Recent lophophore types have to be taken into account when reconstructing the lophophore in fossil forms. Brachiopoda, Lophophorata, lophophore, water system, orientation, evolution.