THE DEVELOPMENT OF RHINCALANUS 



By Robert Gurney 



(Text-figs. 1-7) 



The study of the development of the marine Calanoida presents peculiar difficulties, 

 inasmuch as very few species carry their eggs, and it is consequently rarely possible 

 to identify the nauplius by hatching from the egg. This has only been done in the case 

 of Calanus finmarchicus (Lebour, 1916; Gibbons, 1933). 1 In other cases the series of 

 stages has been laboriously traced out by examination of plankton material, and it is 

 therefore not surprising that, of all the marine Calanoids, we know only the development 

 of the following : 



Calanidae. Calanus finmarchicus. 



Paracalanidae. Paracalanus parvus (Oberg, 1905). 



Pseudocalanidae. Pseudocalattus elongatus (Oberg). 



Centropagidae. Centropages hamatus (Oberg); C. kroyeri (Grandori, 1912); C. 

 typicus (Grandori, 1925). 



Temoridae. Temora longicornis (Oberg). 



Acartiidae. Acartia bifilosa, A. clausi (Oberg); A. clausi (Grandori, 1912). 



There are, it is true, partial descriptions, particularly of copepodid stages, of a number 

 of other forms, but of complete life histories no more are known. I feel, therefore, that 

 no apology is needed for offering a description of the larval stages of Rhincalanus, a 

 genus of the Eucalanidae. 



The material was derived mainly from a plankton sample taken by the R.R.S. 'Dis- 

 covery' at St. 278, off Port Gentil, French Congo, on August 8, 1927. This sample 

 contained numerous nauplii and early copepodid stages of R. comutus, but no adults or 

 copepodids older than stage IV. The later stages have been obtained from other samples 

 taken off the African coast, but in none of them have nauplii or early copepodids been 

 found. The nauplii of R. comutus are all in the last three stages, but a few nauplii of 

 R. nasutus were found in material from St. 93, off Saldanha Bay, south-west Africa, 

 which represent five of the probable six stages. These two series can conveniently be 

 taken together, as the differences between them are very small. 



The nauplius of R. nasutus was identified by Giesbrecht (1893) by observation of the 

 moult to the copepodid stage, and he made use of this elongated nauplius to disprove 

 Claus' statement, which had gained general acceptance, that maxilla and maxillipede of 

 Copepoda are parts of one appendage. It is curious that Claus, who in 1866 had figured 

 an elongated nauplius of the same general form as that of Rhincalanus, did not himself 



1 Since this was written, Mr A. G. Nicholls (1934) has published an account of the development of 

 Euc/taeta norvegica from the egg. 



