TWO PECULIAR ACTINIAN LARV/E FROM TORTUGAS, FLORIDA. 



By Edwin G. Conklin. 



During a residence of about three weeks at the Marine Laboratory of 

 the Carnegie Institution of A\'ashington at Tortugas, Florida, in April and 

 May, 1905, some peculiar actinian larvae belonging to two dii?erent types 

 were several times taken in the tow. These larvae were usually taken toward 

 the middle of the day, rarely in the morning or evening, which fact suggests 

 that they come to the surface during the brightest part of the day and again 

 sink to greater depths when the light becomes faint. 



Several of these larvae were kept during the whole of my stay at Tortu- 

 gas, and Dr. Ma)er, director of the station, kindly reared them and col- 

 lected other specimens for me after my departure, for a further period 

 of six weeks, but during this time no one of them became sedentary or 

 transformed into an adult form. Again, in the summer of 1906, Dr. 

 Mayer collected man\ of these larvae and kept them in aquaria for sev- 

 eral weeks, but no one of them underwent metamorphosis. Finally, I found 

 these larvns in considerable abundance at Nassau, Bahamas, in April, 1907. 

 Although some of the individuals were quite large, no one of them had 

 passed the larval stage. They can not, therefore, be definitely referred to any 

 known species of Actiiiozoan, and although in their structure they show many 

 adult features, they nuist still be regarded as larval, or at least immature forms. 



When first taken these larvae were wholly unknown to the writer, and 

 indeed, while they were still living it was not certain to which ])hylum 

 of the animal kingdom they might belong. One type bore a superficial 

 resemblance to an annelid larva, while the other was apparently unique, 

 but when they were killed and prepared for microscopical study it was easy 

 to see that they belonged to the Actinozoa, and that they were immature 

 or larval forms. On my return from Tortugas a consultation of the litera- 

 ture on this group showed that similar forms had been found in various 

 tropical or subtropical seas and that they probably belong to the family 

 of the Zoanthidas of the order Hexactinia. 



The most striking peculiarity of these larvae is a band of locomotor cilia, 

 which is beautifully iridescent, like the swimming-plates of ctenophores. 

 These cilia are long and extremely numerous, and in living specimens they 



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