424 U. S. BUREAU OF FISHERIES 



As noted previously by other investigators, not all of the eggs 

 deposited develop into young drills. Study siiows that approxi- 

 mately one-half of the eggs laid in the capsules fail to mature. Some 

 develop into abnormal embryos and are eaten by the normal ones. 



Direct evidence of cannibalism has been observed among adults, 

 tlie animals having been drilled amid an abundance of oysters so 

 that starvation conditions could not have been responsible for the 

 attacks. 



JJrosalplnx may undergo its embryonic development in as short a 

 time as 21 days. The fact that the e^^ cases under consideration 

 "vvere allowed to develop in their natural environment where the bot- 

 tom temperature varied between 23.3 and 29.1° C. is stressed em- 

 phatically for it probably affords the explanation of the much shorter 

 time than the 40 days in laboratory tanks at comparable temperatures, 

 reported by another investigator as the time required for hatching. 

 It has also been found that as many as 53 days may be required to 

 complete development. 



Middle and South Atlantic section. — Due to reports that the boring 

 sponge, presumably Cliona celata, was a definite menace to oyster 

 culture in Maryland waters, the Bureau undertook an investigation, 

 assigning Dr. N. A. Wells and Dr. M. Old to study this problem. 

 Through the cooperation of the University of Maryland, lalDoratory 

 facilities were made available at the Chesapeake Biological Labora- 

 tory at Solomons, Md. ; and a boat and captain were provided by 

 the Maryland Conservation Department. 



During the summer representative oyster beds in the IMaryland 

 waters of the Bay and all the major beds in the Potomac and 

 Patuxent Rivers were surveyed. As the investigation progressed 

 it became evident that practically all of the Maryland oyster-pro^ 

 ducing beds were free of Cliona ceJata^ but many of them werej 

 infested to a greater or lesser extent with C. vasti-fica, another 

 species of the same genus which had never been considered of 

 importance as an oyster enemy. At only 2 of the 63 stations was 

 G. celata found on living oysters. At one other station both 

 C. celata and C. vastifca were found on shells, while the sponge at 

 other stations was found to be C. vastiflca. 



Since there were no traces of Clion-a celata at any salinity below 

 15.75, it is thought that this species will not live in a salinity below 

 15 parts per mille, but in order to substantiate this observation, 

 further investigation is necessary. 



The study of the distribution of Cliona vaftti-fi,ca shows that the high- 

 est percentage of infestation occurs between the salinities 11 and 13 

 parts per mille, although C. vastifica infestation is not necessarily 

 at its highest peak wherever this salinity range is found. The 

 lowest salinity in which this species is found appears to be 10 parts 

 per mille while the upper limit has not yet been determined. 



Heavy set and consequent overcrowding produces perfect condi- 

 tions for spread of infestation. Because it is not unusual to find 

 a large clump of oysters in a heavily infested area, entirely free 

 of sponge, it is thought that the principal method of transmission 

 is vegetative. In the laboratory gemmules of Cliona. vastifca were 

 demonstrated, occurring in every case in the marginal perforations 

 and not in the older excavations. Amono- ovsters taken from the 



