68 Bulletin Vanderbilt Marme Museum, Vol. VII 



ACTINARIA 



Family: CERIANTHIDAE 



Genus: PEPONACTIS van Beneden 

 Peponactis aequatorialis (van Beneden) 



Plate 21 



Type : The type of Peponactis aequatorialis van Beneden was 

 taken by "der Plankton-Expedition der Humboldt-Stiftung" at 

 Lat. N. 0.1', Long. W. 15.1°, and is deposited in the Leipzig Zoo- 

 logical Museum. 



Distribution: Apparently widely distributed in the equa- 

 torial Pacific, in depths ranging from the surface down to 400 

 meters. 



Material examined : Fifty specimens, in various degrees of 

 development, taken a dredge haul from the surface to 140 fathoms 

 depth, north of Nuka Hiva Island, Marquesas Islands, Pacific 

 Ocean, August 11, 1931, by the ''Alva." 



Discussion : A remarkably interesting series of larval Cerian- 

 thidae, typical forms of which are shown in plate 21, were taken 

 by the "Alva" in a deep-sea haul north of Nuka Hiva Island. These 

 apparently belong to Peponactis aequatorialis van Beneden (1898) 

 of the typical form described by him, and also are present in con- 

 siderable series possessing intermediate stages between this 

 species and apparently younger stages of it. 



The subspherical specim.ens have a diameter varying from 2.8 

 millimeters with the polar areas flattened, to 3.5 millimeters in 

 the larger of those without tentacles ; the subspherical specimens 

 with the first, rudimentary marginal tentacles present also are of 

 an average diameter of 3.5 to 4 millimeters, with variously ten to 

 twelve marginal tentacles, digitiform, some short and stubby, 

 others five to six times as long as wide. The P. aequatorialis typical 

 forms vary from 4 to 6 millimeters diameter and show the tenta- 

 cles in varying degrees of development, five examples of which are 

 illustrated. The body form of these also varies from subcylindrical 

 to obconic, but specimens of the two extremes, when dissected, fail 

 to show any important histologic differences. The specimens are 



