Two Peculiar Actinian Larva from Tortngas, Florida. 177 



NATURAL HISTORY. 



Apparently no one save Semper has studied any of these forms in a living 

 condition. My observations on the living larvae, although by no means 

 complete, may therefore be of some interest. These larvae were taken in 

 the surface-net, near the middle of the day, and usually in regions where 

 the water was deep. They are quite hardy and will live indefinitely in small 

 aquaria, though they do not grow in size or undergo metamorphosis, even 

 though they be kept for several weeks. 



Zoanthella orients itself so that the blunt aboral pole is directed up- 

 ward, the pointed oral pole downward, and in this position it swims about 

 near the surface of the aquarium, rotating on its long axis in a clockwise 

 direction, when viewed from the oral pole. Its position and movements in 

 the water are the results of the activity of its ciliated band, the undula- 

 tions of which may be plainly seen ; floating is evidently an active process, 

 for when the cilia cease to beat the animal falls to the bottom. The rotation 

 of the larva on its long axis is evidently due to the fact that the ciliated 

 band runs in a slightly spiral course toward the right (clockwise) when 

 viewed from the oral pole. Although the undulations which run from 

 one end of the ciliated band to the other are slow enough to be easily 

 seen, the beating of the cilia at any one level may be so rapid that the 

 individual cilia can not be seen. Under these circumstances the ciliated band 

 appears hazy and broader at its free edge than at its attached border. 



Zoanthina larvre usually lie on the bottom when brought into small 

 aquaria and are motionless, except for the occasional contraction of the 

 ciliated band. These contractions, due to the simultaneous beating of all 

 the cilia toward the oral pole, are not unlike the pulsations of the bell 

 of a jelly-fish, and are so slow and feeble that they do not serve to move 

 the animal. Occasionally, however, many individuals may be found swim- 

 ming rapidly near the surface of the water. This happens especially when 

 stale water, in which they have remained for some time, is replaced by pure 

 water. .\t such times these larvje assume a conical form, the aboral pole be- 

 ing pointed and the oral pole truncated. The deep groove from which the 

 ciliated band arises lies at the border of this flattened oral area and the 

 band itself beats rapidly and violently, the stroke being toward the oral 

 pole. Undulations or irregular contractions of the ciliated band also occur, 

 running around the band in an anti-clockwise direction, when viewed from 

 the oral pole. The resulting movement is quite rapid, the pointed pole being 

 directed forward and the animal rotating in a clockwise direction when seen 

 from the oral pole. When strongly stimulated Zoanthina becomes spherical 

 in shape and the ciliated band disappears within the groove, which closes up. 



Although some of the larvae which I have studied are large and well- 

 developed, no food has ever been found in the ccelenteron ; even diatoms 

 and microscopic algae are lacking. Occasionally fine threads of a coagulum 



