246 BRYOZOA 



History. — The Bryozoa were thought to be seaweeds by the earlier 

 naturalists. Linnaeus grouped theui with the corals and hydroids. Here 

 they remained until 1830, when J. V. Thompson separated them from the 

 polyps because they possess a digestive tube and called them Polyzoa, by 

 which name they are still known by English and many American zoolo- 

 gists. In 1831 Ehrenberg performed the same service and called the new 

 group Bryozoa, which is the name in use among continental and many 

 American zoologists. In 1841 Milne-Edwards created the phylum Mollus- 

 coidea to include the Bryozoa and Tunicata, in which the first named group 

 will still be found in many textbooks. The terms Ectoprocta and Ento^ 

 procta were introduced by H. Nitzsche in 1870. 



About 1,700 species of marine and 35 species of fresh-water Bryozoa 

 are known, which are grouped in 2 classes. 



Key to the classes of Bryozoa : 



Oi Tentacles not retractile into the zooecium 1, Entoprocta 



Oj Tentacles retractile 2. Ectoprocta 



Class 1. ENTOPROCTA.* 



Minute, primitive Bryozoa, in which the anus is within the circle of the 

 lophophore. The body consists of a calyx or head and a contractile 

 stalk, the former containing the viscera. The lophophore is circular 

 and supports a single row of tentacles. The depression within the 

 lophophore, which is called the vestibule, contains the mouth and the 

 anus (Fig. 405) ; projecting over the former is a lip called the epistome. 

 The lophophore cannot be retracted into the zooecium, but the tentacles 

 can be rolled into the vestibule and partly covered by an integumental 

 fold which arises at their base. 



The viscera fill almost the entire space within the body. What 

 space is left and the entire inner portion of the stem are occupied by a 

 gelatinous parenchyma, so that a definite body cavity is wanting. The 

 digestive tube is U-shaped, an oesophagus, stomach, and intestine being 

 distinguishable. The genital organs consist of a pair of gonads which 

 open into the vestibule. The animals are either unisexual or hermaphro- 

 ditic: in Loxosoma davenporti the gonads function as ovaries first and as 

 testes later. A pair of kidney tubules with flame cells open either into 

 the vestibule or the rectum. The nervous system consists of a central 

 ganglion situated between the mouth and the anus and radiating nerves. 



The Entoprocta are found in both salt and fresh water. They are a 

 small group comprising about 20 species, which are grouped in 3 families. 



* See "Studies in Pacific Coast Entoprocta," by A. Robertson, Proc. Cal. Acad. 

 Sci., Vol. 2, p. 320, 1900. 



