Stuflics on mnrino Oslracnds 



117 



abundant effusion of liquid, the lamellae of the shell come together and the body collapses. 

 G. W. MtlLLER writes as follows with regard to this genus, 1895, p. 162: „Wie gesagt, fehlt der 

 Schale jede Spur von Kalkablagerung, zudem tritt die feste Substanz der Leibeshohlenfliissigkeit 

 gegeniiber sehr zuriick, das specifische Gewicht kann kaura hoher als des umgebenden Mediums 

 sein. Fliichenhafte Ausbreitungen fehlen so gut wie bei anderen Ostracoden, doch ist, 

 wie gesagt, der Umfang im Verhiiltnis zur Korpermasse ein sehr groBer, so dafi man sich sehr 

 wohl denken kann, daB das Thier ohne Zuhiilfenahme seiner Ruder wie eine leichte Blase durch 

 das Wasser treibt, ohne unterzusinken." To judge from the development of the second antenna 

 (cf. the description of G. Mulleri below), the species of this genus seem, however, to be at the 

 same time fairly good swimmers. — In most pelagian s t r a c o d s, however, the specific 

 weight has been rather moderately decreased. 



As in the case of tlie Cladocera we are here faced with the question: by what means are 

 these forms kept buoyant? 



To this question I must return the same answer as C. Wesenberg-Lund and 

 R. WOLTERECK gave in the case of the Cladocera: chiefly by swimming. Thus, for instance, 

 a non-swimming Halocyprid sinks to the bottom ,,like a stone". The natatory power 

 of these forms is in point of fact very well developed ; this is especially true of the H a 1 o- 

 cyprids; a very good illustration of this will be found in the information given below in 

 the descriptions of species worked out in the special part of this work. 



Contrary to what is the case in the planktonic Cladocera the shape of the shell in the 

 planktonic Ostracods is subject to rather slight variation. The shells in the planktonic 

 C y p r i d s (only a couple of species, mentioned by C. ApsTEIN, 1907) and the Cypridinids 

 are of about the same types as in the representatives of these groups that live on the bottom; 

 thus all of them are quite without spines and large processes. Even most of the Halocyprids 

 have shells of a very simple, moderately elongated shape without any large processes or spines. 

 A number of representatives of this group are, however, characterized by more deviating types 

 of shells. As examples of forms of the latter kind I may mention the following species: 



Conchoecia daphnoides (C. Claus). This species is distinguished, as is shown by the 

 accompanying fig. XVI, by an elongated fish-like type of shell, the posterior part of the shell 

 is very much lengthened and flattened at the sides, the rostrum is long and wide. 



Other species (e. g. Eucon- 

 choecia aculeata (T. ScOTT) var. 

 elongata G. W. MOller, see G. W. 

 MOlleu, 1906 a, pi. XXXII, 

 fig. 21) resemble this type of 

 shell but are less extremely 

 developed. Conchoecia caudata 

 G. W. MtlLLER is characterized 

 by having the posterior dorsal 

 corner of the right valve and 

 the rostrum on both valves 



By ithat means are 

 the Ostracods with 

 relatively high spec- 

 ific weight kept 

 buoyant? 



The shape of the 

 shell of the plank- 

 tonic Ostracods. 



Fi! 



:. XVL - 



from I he 



■ Tlic 



S\dv. 



shell of Conchoecia daphnoides (C. Claus). ?. — 1. Seen 

 i. Seen from below. (From O. W. Miller, 1906a.) 



