ON LAFCEA DISPOLIANS SP. N. 105 



On Lafoea dispolians sp. n., a Hydroid parasitic 

 on Sertularia bidens Bale. 



By 

 Ernest Warroii, D.Sc.L.oii<l. 



With Plate I and 2 Text-fiL's. 



This liydroid is especially interesting on account of its 

 parasitic habit. 



Only two small colonies have been found ; they both 

 occurred at Isipingo, Natal, and the host was a species of 

 Sertularia. The Sertularia closely resembles S. bidens 

 Bale, recently re-figured and described in the ' Annals of the 

 Natal Government Museum,' vol. i, p. 310. There are, 

 however, certain differences, in that there is no well-developed 

 double tooth of perisarc on the abcauline side of the mouth of 

 the hydrotheca, and also the spiral groove at the base of the 

 pinnate portion of the stem is replaced by an oblique joint. 

 These differences are small and do not appear to be sufficient 

 to justify the formation of a new species. 



Text-fig. 1 represents one of the specimens. The parasite 

 evidently first attacked the hydranth A of the host. Possibly 

 a swimming planula of the Lafcea was swallowed by the 

 polyp of the host, and the subsequent growth of the parasite 

 caused the death of the hydranth of the Sertularia. The 

 hydrorhiza of the parasite then passed through the aperture 

 at the base of the hydrotheca into the ccenosarc of the host, 

 and grew upwards, invading the hydrothecfe B, C and D, and 

 replacing the original polyps of the Sertularia by its own 



VOL. 2, PART 1. 8 



