FISHERY BULLETIN: VOL. 70. NO. 2 



have been common. On several occasions gravid 

 adults have been retained in our tanks and in- 

 duced to spawn, but such attempts were never 

 successful in obtaining their larvae. It is con- 

 sidered, therefore, of importance to document 

 a first success with the species. 



METHODS 



Ten adult H. sorenseni were collected at Santa 

 Catalina Island and transported by ship to San 

 Diego, February 18, 1971." Four possessed 

 gonads sufficiently mature to respond to spawn- 

 ing stimuli. Spawnings were induced on Feb- 

 ruary 21 and 26 and March 1, using the thermal 

 shock method (Ino, 1952), but in no case did 

 fertilization occur in greater than about 5% of 

 the eggs liberated. Observations of larval de- 

 velopment and growth were carried out with 

 progeny (approximately 1,000 trochophore lar- 

 vae) obtained March 1 from a single male and 

 female pair. 



Fertilized eggs were 190 to 200 /a in diameter. 

 Washing of eggs to remove excess sperm, mucus, 

 and other possibly contaminating substances re- 

 leased during or prior to spawning was achieved 

 by repeated suspension in filtered seawater (Mil- 

 lipore' filters, pore size 0.45 jx) following settling 

 and decantation. After incubation of the eggs 

 at 12 ± 2°C for 24-36 hr, larvae hatched at the 

 trochophore stage. Because the swimming 

 trochophores exhibited a strong negative geo- 

 taxis, they concentrated at the surface where 

 they were easily drawn into a Pasteur pipette 

 for transfer to experimental containers. 



The effect of temperature on rate of develop- 

 ment, settlement, and growth of recently settled 

 juveniles was investigated using an aluminum 

 thermal gradient block (Thomas, Scotten, and 

 Bradshaw, 1963) with compartments bored to 

 accommodate a series of 100-ml beakers. Each 

 compartment could be illuminated from beneath 

 to permit growth of algae within beakers. Con- 



" Collections were made at a depth of about 70 ft by 

 T. Tutschulte and were timed to sample the peak of the 

 reproductive season at the Isthmus station. 



° Reference to trade names in this publication does not 

 imply endorsement of commercial products by the Na- 

 tional Marine Fisheries Service. 



tainers, arranged in duplicate, were maintained 

 at 10, 12, 14, 16, 18, and 20°C (each ± 0.5°C). 

 The Pyrex beakers received 80 ml of Millipore- 

 filtered and ultra-violet light treated seawater 

 (Loosanoff and Davis, 1963). Twenty 72-hr 

 veliger larvae were introduced into each togeth- 

 er with 1 ml of a suspension of the food orga- 

 nism, Nitzschia sp,, containing approximately 

 10,000 cells. To guard against salinity changes 

 due to evaporation or condensation, each beaker 

 was covered with a paraffin sheet, and the entire 

 block insulated with foam styrene. Inspection 

 was made on alternate days to determine the 

 number of larvae surviving, settlement, and 

 growth rate. The water was changed once 

 weekly and new food supplied. 



Approximately 500 larvae were distributed 

 among five 1-liter Pyrex beakers at the time the 

 thermal gradient erperiment was begun. These 

 containers received a combination of about 10 

 species of pennate diatoms collected from illu- 

 minated aquarium surfaces in the laboratory 

 (chiefly Nitzschia, Grammatophora, and Navic- 

 ula). A thermal environment of 15-17°C was 

 maintained. 



DESCRIPTION OF LARVAE 



The reader seeking details of morphogenesis 

 in haliotids should refer to illustrations and text 

 as provided for Japanese species by Ino (1952) 

 and Oba (1964), early development of which 

 closely parallels American members of the genus. 

 In this paper an efl!"ort is made to indicate dis- 

 tinctive features of H. sorenseni larvae, 



Trochophores were subcylindrical in outline, 

 bore a distinct prototroch and were yellow-tan 

 in color. At 15-16°C, the roughly symmetrical 

 shape of the trochophore was soon lost and by 

 48 hr after fertilization the early veliger form 

 was attained with the incipient cap-shaped shell 

 and lobular velum becoming defined. At 72 hr, 

 the larval shell had taken the typical gastropo- 

 dan snail-form complete with operculum while 

 shell musculature, viscera, eye-spots, and velum 

 were well developed. At the same time the foot 

 and cephalic tentacles began to diflE"erentiate 

 (Figure 1). Tissue pigmentation was predom- 

 inantly beige, velar fringes were yellow, and the 



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