Functional disposition of the lophophore in living Brachiopoda

The shape and disposition of adult brachiopod lophophores relate to inand 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 ( l o % ) 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 Megathiris 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 n 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. ‘L Brachiopoda, Lophophoruta. lophophore, wirer s js tem, orienmtion, eoolurion.