558 



Phylum Echinodermata 



NOTES ON THE CULTURE OF STRONGYLOCENTROTUS 

 FRANCISCANUS AND ECHINARACHNIUS EXCENTRICUS 



Martin W. Johnson, Scripps Institution of Oceanography 



THE animals were usually cultured in section jars of about 500 cc. 

 capacity. The water used was always fresh seawater carried to the 

 laboratory in glass or enameled buckets and filtered through No. 20 silk 

 bolting cloth. An even temperature was maintained by placing the 

 dishes in the laboratory sink through which there circulated a stream of 

 water previously cooled by flowing through pipes submerged in the bay. 

 No special means of aeration was used but the specimens were never 

 allowed to be crowded. Cultures of diatoms were added to the dishes 

 when they were set up or shortly after. These diatoms were of mixed 

 species but always contained a fair number of Navicula living as indi- 

 vidual cells. A good supply of diatoms could usually be obtained in a 

 couple of weeks by allowing a very slow stream of salt water to flow as a 

 film over a large glass plate. 



Strongylocentrotus jranciscanus. The eggs and spermatozoa were 

 obtained by breaking away a portion of the test near the genital pore of 

 ripe adults. A few minutes after insemination the water was decanted 

 and fresh seawater added. This operation was repeated two or three 

 times till the water appeared clear. Each dish set up had a concentra- 

 tion of eggs such that an even distribution would allow the eggs to 

 be separated by about 2 to 3 mm. The early larvae swim about in the 

 upper portion of the water and the lower half may be siphoned away 

 with a small rubber tube to which there is attached a glass tube which 

 may be moved over the bottom to pick up the undeveloped eggs or 

 weakened larvae. The whole operation should be watched closely in 

 order to avoid removing too many of the healthy larvae. It has appeared 

 advisable to carry on the cultures in the same dish, for the accumulation 

 of loosely attached diatoms appears to contribute food to the larvae. 

 A portion of the water was renewed every day for about one week and 

 thereafter at intervals of about a week. There was always a rather 

 high mortality and many were lost in the changing of water but a fair 

 number of specimens were carried through to the beginning of meta- 

 morphosis, and a few specimens were well advanced at 62 days. The 

 temperature never exceeded 12 ° or 13 ° C. 



Echinarachnius excentricus. The methods were the same as for 

 5. jranciscanus except that the eggs and spermatozoa were obtained from 

 spawning adults. A few specimens cultured thus completed meta- 

 morphosis in 72 to 80 days. The highest temperature was 16.1 but 

 was usually near n° C. 



