CHELURA TEREBRANS PHILIPPI 93 



of four months, when the limnoriids had a good start, twenty chelurids 

 were added to one of the aquaria and the other was kept as a control. 

 After twelve more months of exposure the blocks were examined and 

 were so similar in appearance as to defy any gross differentiation (see 

 figs. 2B, D). Both blocks showed surface troughs "typical" of chelurid 

 action alone, indicating that limnoriids were capable of making these 

 same troughs. Howe\'er, it must be noted that the limnoriid population 

 in the control block had grown so large that individual animals were 

 seen at the surface of the block. On the chelurid-limnoriid block only 

 chelurids were seen at the surface. It is possible that under idealized 

 laboratory conditions (clean water and lack of predators) the limnoriids 

 had multiplied to such an extent that space was scarce and many were 

 forced to browse at the surface. In nature, the writer has watched 

 heavily infested pieces of wood for as long as 75 minutes without seeing 

 limnoriids moving at the surface. 



DEPENDENCE OF CHELURIDS UPON LIMNORIIDS 



The general ecological dependence of chelurids on the activities of 

 limnoriids was ably summarized by Yonge (1949, pp. 186-187) : Chelura 

 "probably enlarges pre-existing cavities but it is doubtful whether this 

 animal can excavate a burrow unaided by the previous activities of the 

 gribble." It "always lives in the more superficial layers of the wood 

 which have already been honeycombed with the formation of channels 

 and pits in which it can live protected." If one considers Chelura in its 

 natural environment, the statements made by Yonge are valid. We have 

 seen that under artificially protected conditions chelurids will excavate 

 their own furrows on smooth wood ; but it is assumed that predation 

 would eliminate any of these animals attempting to do this in nature, or 

 that chelurids would reject smooth wood in favor of eroded wood. One 

 must also consider the fact that chelurids are more sensitive to environ- 

 mental conditions than are limnoriids, as the latter are found in great 

 abundance in certain parts of Los Angeles Harbor unaccompanied by 

 chelurids. This is true in many other harbors, as evidenced by the vol- 

 uminous data on borers presented in the various Clapp reports (Clapp, 

 1951-1954). Evidently, the need for a preformed, protected burrow 

 makes Chelura dependent on the prior activities of a species of Limnoria, 

 but Chelura does not always occur where Limnoria has established a 

 favorable niche. 



Johnson et alia (1936, p. 19) suggested in relation to the immunity 

 of hardwood from Chelura that it is due to "the size and shape of 

 Chelura, and not to a difference in boring ability. Hardwood provides 



