1922] Blum: On the Effect of Low Salinity on Teredo Navalis 353 



OBSERVATIONS 



Effect of Low Salinity 



Decrease in activity. — In considering the effect of reduced salinity 

 on the activity and function of Teredo navalis a brief resume of the 

 normal mode of life of the organism is necessary. In the adult stag'e, 

 the teredo is established in a long, slender burrow which it has drilled 

 into a pile or other wooden object. The maximum size of the burrow 

 is about five-sixteenths inch in diameter and twelve to sixteen inches 

 in length. It is lined with pearly nacre except at the inner end in 

 the region of the shell where boring activity goes on. The outer end 

 of the burrow tapers to a minute opening through which two siphons 

 are extended for the purposes of obtaining water containing food 

 material and of ejecting excreta and wood chips resulting from boring 

 activities. By means of these siphons, water is constantly circulated 

 through the mantle cavity and burrow. The siphons are normally 

 very sensitive and are quickly retracted when touched by a solid 

 object. The organism is equipped at the siphonal end with a pair of 

 small wedge-shaped pallets with which it may effectively plug its 

 burrow 7 when the siphons are drawn in. It is thus able to prevent 

 intrusion of other animals and to avoid adverse conditions in the 

 water outside the burrow by blocking the entrance of such water into 

 its burrow. 



When the salinity of the water becomes sufficiently low, the 

 teredos draw in their siphons and plug up their burrows with the 

 pallets. The point at which this occurs may be considered as the 

 salinity below which full normal functioning is impossible. The 

 following experiments were performed to determine this salinity. 



Specimens were first acclimatized by placing them in standing 

 straits water of 15 parts per 1000 salinity for two to four days. 

 During this period a daily record was kept of the number of siphons 

 extended from the specimen block, this number being taken as the 

 original 100 per cent for the given specimen. The specimens were 

 then changed to salinities of 0, 2, 4, 5, 6, 7, 8, 9, or 15 parts per 1000. 

 A record was kept of the number of siphons extended from each 

 specimen block during the periods of exposure (about three weeks) 

 to these several lower salinities. Ten specimen blocks in individual 



