MOLLU8COIDEA. 105 



Phylum IV. MOLLUSCOIDEA. 



Sedentary, almost exclusively marine animals, with a lophophore 

 bearing ciliated tentacles, an epistome, house or bivalve shell, and one 

 or several ganglia. Prseoral region much reduced or absent. Mouth and 

 anus generally approximated. Body elongated at right angles to the oro- 

 anal axis. 



See note, p. 39. 



Class I. Polyzoa (Bryozoa). 



Small forms, usually colonial, and with sexes united. Development 

 with a metamorphosis. ^/r 



Order 1. Vermiformia. Social Polyzoans enclosed in leathery tubes ; 

 lophophore horseshoe-shaped. Nervous system as a ring round the mouth 

 and a body-nerve. A system of blood-vessels, enterocoelic body-cavity, 

 and two nephridia. Only known genus Phoronis, with Actinotrocha 

 larva. 



Order 2. Eupolyzoa. Almost all colonial. Contained in cells formed 

 by the thickened cuticle. Nervous system as a single ganglion. No 

 vascular system. Budding always occurs. 



Endoprocta. Anus within the lophophore, which can only be 

 partially retracted. No proper body-cavity. Nephridia. Pedicellina 

 echinata, colonial. Loxosoma, non-colonial. 



Ectoprocta: anus outside the lophophore, which can be com- 

 pletely retracted. An enterocoelic body-cavity. Oristatella, Pluma- 

 tella, Alcyonella, in fresh water, with horseshoe-shaped lophophore ; 

 statoblasts. Tentacles in a circle in most marine forms : Eetepora. 

 Membranipora, Flustra, Alcyonidium. 



