monoE 



DISCOVERY REPORTS 



Of the sixteen species of Sergestes known from the Atlantic and included in Hansen's 

 5graph we have been able to follow the development completely, or in part, of thirteen. 

 The development of S. mollis, S. grandis and S. splendens remains completely unknown. 

 These are species of very deep water, and it is possible that they do not occur in the 

 immediate neighbourhood of Bermuda. We have, both from Bermuda and from the 

 Discovery material, larvae which it is impossible at present to identify. It is suggested 

 that they may belong to species as yet undescribed. 



Nakazawa states that S. prehensilis starts its life-history as a Nauplius. We have been 

 unable to read the paper, which is entirely in Japanese, and do not know what evidence 

 he is able to give. The figures show the Nauplii to be entirely unlike those of any other 

 Penaeid, and they appear to have all the characters of Copepod Nauplii. Wasserloos was 

 unable to find any evidence for the existence of a Nauplius in S. arciiciis, and we have 

 seen no Nauplii attributable to Sergestes. It is by no means impossible that there is such 

 a stage, since there is a Nauplius in Lucifer and Acetes, but it will be most difficult to 

 prove or disprove its existence. The Nauplius phase may be very rapidly passed through, 

 probably at night, and it would have to be sought in the strata occupied by the adult. 



Our main purpose in this report is to describe the Elaphocaris and Acanthosoma stages 

 of the Atlantic species, but we have also included descriptions of the first Mastigopus, 

 and, in some cases, have given figures of later stages also, since we believe that figures 

 of the whole animal are valuable aids to identification. Detailed descriptions of the later 

 Mastigopus stages are unnecessary, since they have been so fully dealt with by Hansen ; 

 but he was not usually in a position to determine, as we have done in some cases by 

 moulting, the actual first stage. It is to be understood that we have reUed entirely upon 

 Hansen's monograph in the identification of the species dealt with, since this is the most 

 complete and authoritative account of the genus published ; but there is some evidence 

 from the larvae that there exist species which Hansen did not discriminate. 



Mr Burkenroad informs us that some of Hansen's species (e.g. S. comicidwn) are 

 certainly composite, and Dr I. Gordon has recently described a new species of the 

 robustus-gvoxi^ from the Atlantic. 



Hansen has laid great stress upon the depth of colour of the eye pigment, stating that 

 it is always brown up to the end of the Mastigopus phase, and black thereafter. This we 

 do not find to be the case when living material is available. In all species the eye is black 

 or dark brown from the earliest stages, but it becomes lighter, or even colourless, in 

 formol and spirit. 



In the descriptions which follow we have found it difficult to decide upon a terminology 

 for the armature of the carapace. While the outgrowths of the carapace are homologous 

 in Elaphocaris and Acanthosoma they have been described as processes in the former 

 and spines in the latter simply as a matter of convenience, since, in the former, they may 

 themselves bear spines. In both cases the outgrowths may also bear spinules or prickles, 

 and the objectionable term "long spinules" has been used when the armature is inter- 

 mediate between prickles or spinules and longer outgrowths which can definitely be 

 called spines. We have laid stress upon the number of spines on the processes in the 



