CHELURA TEREBRANS PHILIPPI 89 



SELECTIVITY IN BURROWING 



The furrows produced by the chelurid populations were made by col- 

 lective activity rather than individual effort. Ten animals in one experi- 

 ment were observed daily for 30 days in order to plot their positions in 

 relation to individual furrows. Each animal was recognizable by its size 

 and sex. The movements and positions of each animal for the time period 

 were random, indicating that individual furrows were the result of the 

 browsing action of several chelurids. 



CHARACTER OF CHELURID POPULATIONS 



Eight Douglas Fir blocks were strung on a weighted rope and sub- 

 merged beneath the pier at the California Yacht Basin in outer Los 

 Angeles Harbor. One of these blocks was collected every 28 days, pre- 

 served in 4% formalin and subsequently dissected with knives and needles 

 and the animals counted. Both Chelura terebrans and Limnoria tripunc- 

 tata Menzies (1951) were found in these blocks. 



The data presented in fig. lA shows that L. tripunctata invaded the 

 block during the first month of exposure, while C. terebrans did not 

 appear until the third month. Fifteen similar experiments, tried at other 

 places in the harbor, showed that in some cases where limnoriid activity 

 was particularly high, up to eight chelurids would be found as early as 

 the first month of exposure. However, no chelurids appeared on the test 

 blocks placed in the inner harbor although at several of these stations 

 limnoriid activity was higher than at some of the stations in the outer 

 harbor where Chelura occurred. Chelurids were also found with another 

 limnoriid, L. quadripunctata Holthuis (1949). 



In all of the induced population experiments, at the first appearance 

 of chelurids, whether in the first or the fourth month of exposure, there 

 were already present from four to twelve times as many limnoriids. The 

 first limnoriids appeared in almost circular burrows, the openings of 

 which led into tunnels lying parallel or slightly oblique to the wood 

 surface. Other adult limnoriids, as w^ell as juveniles hatched from the 

 first migrants, started burrows of their own in or near the openings of 

 the first holes, thus enlarging the size of the original cavities. Increase 

 in the number of burrows resulted in an irregular honeycombing of the 

 area. Partitions between some burrows were paper-thin and roofed-over 

 caverns appeared. It was in these exposed limnoriid galleries that the 

 first chelurids were found. 



The first chelurid inhabitants were always adult or sexually mature 

 animals while juvenile animals appeared a month or more later. It was 



