ROCK-BORING ORGANISMS 

 R 



15 



Fig. 6. Rocellaria (Gastrochaena) cuneiformis. Above, animal in situ in 

 boring; below, transverse sections in regions a to d. CL, calcareous lining 

 secreted by walls of siphons (not shown) and forming projecting exhalant 

 (£S) and inhalant (IS) siphonal tubes; F, suckerlike foot; H, hinge region; 

 M,' mantle exposed in anterior pedal gape; P, pedal opening; R, rock; V, shell 

 valve. Broken line denotes inner limit of secreted calcareous lining of boring. 

 (After Otter, 1937.) 



the Pholadidae, but must abrade as a result of water pressure aided 

 by the opening thrust of the long ligament. A striking feature of 

 Rocellaria (indeed of the entire superfamily) is the capacity of the 

 siphonal tissues to secrete calcium carbonate (Shiiter, 1890), so 

 lining the boring and extending this beyond the rock surface into 

 two tubes formed by the separated ends of the siphons (Fig. 6, ES, 

 IS ) . The boring is oval in section ( Fig. 6 c, d), indicating, together 

 with the fixed position of the siphonal tubes, that the animal bores 

 directly into the rock. The borings appear to be much longer than 

 even the long siphons, and possibly, unlike the Pholadidae, these 

 animals can move backward and forward within the boring. A 

 byssus gland persists, and occasionally threads are secreted. This 

 fact, together with the habits of related genera, indicates that here 

 also boring has followed an initial epifaunal habit. 



