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CHAPTER XVIII 



NOTES ON THE BIOLOGY OF OTHER PACIEIC SHIPWORMS 



In view of thi' extended discussion of the i)iology of Teredo navalis given in 

 preceding chapters it will suffice to mention rather liriell\- the salient features of the 

 life history and habits of the se\-eral other shipwornis occurring in Pacific waters, inso- 

 far as these are known. The order followed below is that of the econf)mic importance 

 of the organisms discussed, rather than the order of systematic zoology, which was 

 followed in Chapter XIII, where also the characters distinguishing the various species 

 were set forth. 



Banki..\ setace.\ 



This species has been called the "Northwest Shipworm" While it occurs com- 

 monly in Los Angeles Harbor and in somewhat limited numbers in San Diego Bay, 

 its capacities for damage are most fully realized in the harbors from San Francisco 

 Bay northward. The most northern limit of its distribution has not been deter- 

 mined, but its range includes the Alaskan coast, at least to Kodiak Island. The 

 species is apparently native to the Pacific Coast of North America; it has been here 

 since the earliest history of shipping on this coast, and has not been reported as 

 occurring elsewhere. 



In several aspects of its habits and relations to physical factors of the en\ironment 

 Bankia setacea differs so decidedly from Teredo navalis as to merit special remark. 

 The breeding habits, as noted in an earlier chapter, are fundamentally different. 

 Instead of the eggs being fertilized internally and retained in the gills of the female 

 until a fairly advanced stage of larval development is reached, as is the case in T. 

 navalis, T. diegensis and others, in Bankia the eggs are extruded into the water, 

 fertilization and the successful development of the egg to the stage of the bivalve 

 larva being matters of chance and considerable hazard. Hence, although an enormous 

 number of eggs is produced by a single female, the number of lar^•ae finding settlement 

 is relatively small as compared with the incubatory species. 



Further, the breeding season is relatively short, commencing in February or 

 March, reaching a maximum in April or May, and as a rule coming to a close before 

 July. Females bearing eggs apparently mature were found at Angel Island on August 

 24, 192L in test boards placed April 25 preceding, and also along the San Francisco 

 waterfront on August 18, 1922, in piling driven in February preceding. These findings 

 would indicate the possibility of an autimin as well as a spring breeding season for 

 this species; but the only indication of settlement of larvae later than June was the 

 finding at Goat Island, on Septeml)er 15, 1921, of one small specimen of Bankia 

 setacea in a test board placed in the water Juh' 15 preceding. It would seem therefore 

 that the conditions prevailing during the late summer and autumn are not favorable 

 to the development and settlement of larvae of this species. 



Observations indicate that the most important single factor influencing the 

 breeding activities of Bankia setacea is temperature, with which factor the breeding 

 season appears to be inversely correlated. Thus in San Francisco Bay the breeding 

 season begins about February, when water temperatures are nearly at a minimum 

 for the year, and ceases in general at the beginning of summer. In Alaskan waters, 

 where temperatures are considerably lower, the breeding season for this species begins 

 a month or more earlier than in San Francisco Bay. A test board placed at Petersburg, 



