BRACHIOPODA 613 



Class EcTOPROCTA. Polyzoa with anus outside the lophophore; with 

 a coelomic body cavity and a lophophore retractile into a tentacle 

 sheath; without definite excretory organs. 

 Order Phylactolaemata. Freshwater Ectoprocta with a horseshoe- 

 shaped lophophore, an epistome and statoblasts. Plumatella^ 

 Cristatella. 

 Order Gymnolaemata. Ectoprocta mostly marine, with a circular 

 lophophore, without an epistome, with various types of trocho- 

 sphere larva. 

 Suborder Cyclostomata with tubular zooecia, aperture without 



operculum, embryonic fission characteristic. Crista. 

 Suborder Cheilostomata, with aperture of zooecium closed by an 



operculum. Bugula, Flustra, Memhranipora. 

 Suborder Ctenostomata with aperture of zooecium closed by a 

 folded membrane when the lophophore is retracted. 

 Alcyonidium. 



It is possible that the Endoprocta should be separated from the 

 Ectoprocta as a distinct phylum and associated with forms like the 

 rotifers. 



PHYLUM BRACHIOPODA 



Coelomate unsegmented animals with a bivalve shell which is always 

 attached, the valves being respectively dorsal and ventral in position; 

 a complex ciliated circumoral organ, the lophophore^ which maintains 

 a circulation of water in the mantle cavity and leads food currents to 

 the mouth. 



The group contains only marine animals with a strong but super- 

 ficial resemblance to the lamellibranchs among the Mollusca. In the 

 Palaeozoic and Mesozoic it was more abundantly represented than 

 the Mollusca, but at the present day it contains but few genera and 

 species. Of the former Terebratula and Waldheimia (in which the 

 valves meet to form a hinge and which belong to the Testicardines) 

 are found in deep water off our own coasts. Examples of hingeless 

 forms (Ecardines) are Crania which occurs abundantly in shallow 

 water in the West of Ireland, and Lingula, which is not found in 

 Britain, but in the tropics is sometimes exceedingly abundant in 

 mud between tidemarks. 



In such forms as Waldheimia and Terebratula (Figs. 422, 423), the 

 ventral shell valve is larger than the ^dorsal and has a posterior beak 

 or umbo perforated by a round aperture through which passes the 

 stalk for attachment to a stone or rock. Each valve is secreted by a 

 corresponding mantle flap, but in a way which diflFers from the corre- 

 sponding process in the Mollusca. The mantle epithelium is produced 



