MOLLUSCOIDA I POLYZOA. 



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tubular, non-retractile tentacles, which have their sides ciliated, 

 and are arranged sometimes in a circle and sometimes in a 

 crescent. In the fresh-water Polyzoa the tentacles are united 

 towards their bases by a funnel-shaped membrane, known as 

 the " calyx." The tentacles are borne upon a kind of disc, or 

 stage, which is termed by Professor Allman the " lophophore." 

 In the majority of Polyzoa including almost all the marine 

 species the lophophore is circular (fig. 124, 2) ; but in most of 

 the fresh-water forms it has its neural side extended into two 

 long arms, so that the entire lophophore becomes crescentic 

 or " horse-shoe-shaped " (fig. 124, 3); hence this section is 



Fig. 124. i. Fragment of Flustra iruncata, one of the Sea-mats, natural size. 2. A 

 single polypide of Valkeria, magnified, showing the ortrcular crown of tentacles. 

 3. A polypide of Lophopus crystallinus, a fresh-water Polyzoon, highly magnified, 

 showing the horse-shoe-shaped crown of tentacles : a Tentacular crown ; b Gullet ; 

 c Stomach ; d Intestine ; e Anus ; g Gizzard ; k Endocyst ; / Ectocyst ; f Funiculus. 



sometimes collectively termed the " Hippocrepian " Polyzoa. 

 In all, or almost all, the Polyzoa in which this crescentic con- 

 dition of the lophophore exists, there is also a singular valve- 

 like organ which arches over the mouth, and is termed the 

 " epistome." The only marine forms in which the lophophore 

 is bilateral are Pedicellina and Rhabdopletira ; the only fresh- 

 water species in which the lophophore is orbicular are Paludi- 

 cella and Urnatella. 



The mouth conducts by an oesophagus into a dilated stomach. 

 In some cases a pharynx may be present, and in others there 



