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abundant effusion of liquid, the lamellae of the shell come together and the body collapses.
G. W. MULLER 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 Leibeshöhlenflüssigkeit
gegenüber sehr zurück, das specifische Gewicht kann kaum höher als des umgebenden Mediums
sein. Flächenhafte Ausbreitungen fehlen so gut wie bei anderen Ostra Coden, doch ist,
wie gesagt, der Umfang im Verhältnis zur Körpermasse ein sehr großer, so daß man sich sehr
wohl denken kann, daß das Thier ohne Zuhülfenahme 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. Mülleri below), the species of this genus seem, however, to be at the
same time fairly good swimmers. — In most pelagian Ostracods, however, the specific
weight has been rat-her moderately decreased.
As in the case of the 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: chieflv 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 faet very well developed; this is especially true of the
Halo-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. ApsTEIX, 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 mueh lengthened and flatt-ened at the sides, the rostrum is long and wide.
Other species (e. g.
Eucon-choecia aculeata (T. SCOTT) var.
elongataGr. W. Müller, see G. W.
MULLER, 1906 a, pl. XXXII,
fig. 21) resemble this type of
shell but are less extremely
developed. Conchoecia caudata
G. W. MULLER is characterized
by having the posterior dorsal
corner of the right valve and
the rostrum on both valves
Fig. XVI. — The shell of Conchoecia daphnoides (C. Claus), $. — 1. Seen
from the side. 2. Seen from below. (From G. W. Müller, 1906a.)
By what means are
the Ostracods with
relatively high
specific weight kept
buoyant?
The shape of the
shell of the
planktonic Ostracods.
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