'..VAr 





^ '■* 



^ 



^ 



Figure 380.^Black pustules on the surface of the visceral mass and mantle of C. virginica caused by contact with boring 

 sponge, Cliona celaia. Photograph of an oyster kept in the laboratory tanks at Woods Hole. 



edges. The worm accumulates mud and builds 

 a U-shaped tube which is covered by semitrans- 

 parent shell material secreted by the oyster. 

 The formation is usually called a blister. P. 

 ligni is abundant on tidal flats where it can be 

 found living in small mud tubes or in crevices 

 of waterlogged wood structures and other sub- 

 merged objects. The mud worm may be in- 

 directly destructive to oysters, for when many 

 worms settle on shells they can smother an entire 

 oyster population with their tubes. P. ciliafa 

 (Johnston) has been accused of extensive mortali- 

 ties of oysters in New South Wales, Australia 

 (Roughly, 1925). Frecjuent reports of finding 

 this species on the coast of eastern America are 

 based on erroneous identifications and probably 

 should be referred to as P. websteri (Hartman, 



1945). Korringa (1951b) finds no serious in- 

 juries by P. ciliata to oysters {0. edulis) in Dutch 

 waters and thinks that in many areas the damages 

 were caused by P. websteri and P. hoplura. 



Ivnowledge of the life histories of P. websteri 

 and P. ligni is incomplete. Both species lay 

 eggs in capsules attached to the inner walls of 

 the tube in which the animal lives. The egg- 

 laying was noticed in the Woods Hole laboratory 

 when P. ligni were placed in small glass tubing 

 of appropriate lengtii and diameter (fig. 382). The 

 process of egg laying has never been observed in 

 spite of frequent examination of several tubes dur- 

 ing both day and night (Mortensen and Galtsoff, 

 1944). However, egg capsules were found 

 attached to the walls of the tubes shortly after 

 Polydora were left undisturbed in darkness. 



422 



FISH AND WILDLIFE SERVICE 



