PSEUDOCOELOMATE AND MINOR EUCOELOMATE PHYLA 



undifferentiated mass of cells. The individual thus developed soon produces 

 other zooids by a process of budding, and a branching colony is formed. The 

 majority of the marine relatives of Bugula have similar life cycles but form 

 plate-like, encrusting colonies in which each zooid is encased in a rigid, 

 limy shell or zooecium (Fig. 12.10). 



The colonies of ectoprocts in fresh water are also of two types. Some are 

 branching, like Plumatella, which is supported by a skeleton of chitinous 

 material. In others, such as Pectinatella, the skeletal secretion takes the 

 form of a large, gelatinous mass, in the surface layers of which the bodies of 

 the zooids are embedded (Fig. 12.13). These fresh-water ectoprocts repro- 

 duce sexually and also by an asexual process involving the formation of 

 internal buds, or statoblasts. These become covered by hard, brown, chitinous 

 shells and in autumn and winter may be found in large numbers floating or 

 entangled in submerged vegetation. Like the gemmules of sponges (pp. 280- 

 281), they can withstand freezing, desiccation, and other unfavorable con- 

 ditions and eventually germinate to develop into new colonies. 



THE PHYLUM BRACHIOPODA 



The Brachiopoda, or lamp shells, are marine animals attached to the sub- 

 stratum by a stalk and enclosed in bivalve shells somewhat resembling those 

 of clams. In the brachiopods, however, the valves appear to be paired dorso- 



Fig. 12.12. Larvaeof marine ectoprocts. A, cyphonautes larva of Eledra pilosa; this is 

 a feeding stage, with a complete digestive tract. B, non-feeding, transitory larva of 

 Hugula. C\ larva of Alcyonidium: note the reduced and non-functional digestive cavity. 

 (Redrawn, after various authors, from C. Cori in W. Kiikenthal and T. Krumbach, 



1938, Ham/huch der ^ooloaie.) 



361 



