No. XXIII.— PELAGIC ACTINIAEIAN LARV^. 



By Edith E. Bamford, Newnham College, Cambridge. 



(Plates 23 and 24.) 

 (Communicated by Prof. J. Stanley Gardiner, M.A., F.R.S., F.L.S.) 



Read 2nd November, 1911. 



The collection of Actinian larvse from the Indian Ocean, though small, proves to be 

 of considerable interest. It consists of thirteen different types ; of these four belong to 

 the group Zoanthidea, three to the Cerianthidea, and the remaining six probably to the 

 Actiniaria. The chief interest of the collection lies in the four Zoanthidean larvse ; they 

 are all new species of the genus Zoanthina (v. Beneden *), and they form a considerable 

 addition to the few species so far recorded. There are only single specimens of all the 

 types in the different groups with the exception of one Zoanthina, which has two 

 representatives. 



The larvse were brought home in formalin in seawater. Subsequently they were 

 put into a saturated solution of corrosive sublimate for one hour and stained with borax 

 carmine. Serial sections were cut at right angles to the oro-aboral axis and stained with 

 picronigrosin. The second larva of the Zoanthidean with two representatives was cut 

 longitudinally. 



Zoanthidea. 



Four different forms of larvse are assigned to this group, but they all belong to the 

 same type as Semper's first larva, to which v. Beneden gave the generic name, Zoanthina. 

 Carlgren slightly modified and extended the diagnosis of the genus : " Pelagische Antho- 

 zoenlarve von eiformiger Gestalt mit einer ringfdrmigen, transversal verlaufenden, 

 geisseltragenden, tiefen Furche, die den Korper in zwei Partien, einen oralen kleineren, 

 die die Mundscheibe und das Schlundrohr enthalt, und einer aboralen grosseren, mehr lang 

 gestreckten, teiltf." 



The four forms belong to undescribed species. Larva IV. is rather discoidal than 



egg-shaped. All have twelve mesenteries, of which six are incomplete, among them being 



the dorsal directives. Three of the species have the microtype arrangement of mesenteries, 



but larva II. has the microtype arrangement on one side and the macrotype on the other. 



Of this arrangement Duerden| recorded examples as a variation in adults of Palythoa 



mamillosa (Ell. & Sol.), Palythoa caribcea (Duch. & Mich.) and Gemmaria variabilis 



(Duerden), both genera belonging to the Zoanthidea. The endodermal swellings on 



* Plankton Expedition, Les Anthozoaires, 1898, p. 196. 

 t Nordisches Plankton, Zoantharien Larvre, xi. 1906, p. 89. 

 I Trans. Roy. Dub. Soc. 2, vi. 1898, Jamaica Actinia;, p. 331. 



