vm 



PHYLUM MOLLUSCOIDA 



347 



tent 



tenf 



Tertiary the latter sub-order greatly outnumbers the Cyclostomata. 

 The Tertiary Polyzoa nourished in certain localities in such 

 luxuriance that their remains form calcareous deposits of very 

 great extent. 



Sub-Class II. Endoprocta. 



While the sub-class of the Ectoprocta comprises a large number 

 of genera, that of the Endoprocta includes only P&diceUina (Fig. 288), 

 Loxosoma, Urnatella, Myosoma, Gonnpoddria and Ascopodaria, with 

 one or two other less completely kno\vn forms. They are all 

 marine except Urnatella an American fresh-water genus. The 

 feature indicated by the name of the sub-class viz. the position 

 of the anus within the circlet of the tentacles, is an important 

 point of difference from 

 the rest of the class ; but 

 there are others of as great 

 or greater importance. 



In none of the Endo- 

 procta is there a distinct 

 introvert. The body is 

 cup-shaped, with a rim 

 which is capable of being 

 inverted over a cavity 

 - the vestibule within 

 which the tentacles can 

 be withdrawn, and which 

 contains both mouth and 

 anus. An epistome over- 

 hangs the mouth. The 

 ccelome is almost or quite 

 obliterated, the space 

 between the alimentary 

 canal and the wall of the 

 body being filled, more or less completely, with a gelatinous hyaline 

 matrix. A pair of nephridia are present. In Loxosoma they lie 

 one on either side of the oesophagus and open separately on the 

 exterior ; they are ciliated intra-cellular tubes, each of which 

 probably begins in a flame cell. In Urnatella the two nephridial 

 tubes unite to open into the cloaca a diverticulum of the 

 vestibule. The ganglion (Fig. 288, gang.), situated between mouth 

 and anus as in the Ectoprocta, is bilobed in Loxosoma. Testes and 

 ovaries occur in the same individual in some, but appear to mature 

 at different times : they are provided with special ducts ; in others 

 the sexes are separate. 



Pedicellina and Urnatella are colonial, Loxosoma solitary. In 

 Pedicellina (Fig. 288) there is a creeping stolon with which a 

 number of zooids are connected ; a diaphragm separates the body 



FIG 288. Pedicellina. Showing successive stages 

 \numbered 1 to 6) in the developmeut of zooids by 

 hurtdin". an. anus ; aang, ganglion ; mo. mouth ; 

 /en/, tentacles (retracted). (After Hatschek.) 



