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234
anal segment obtusely produced behind. Basal expansion
of antennulse divided
behind into 6 coarse teeth. Coxal plates very distinctly pectinate. Outer ramus
of uropoda extremely small, scarcely half as long
as the inner. Colour whitish.
Length of adult female 2.10 mm., of male 0.90 mm. Parasitic on Cypridina
norvegica, occupying the part of the shell-cavity
ova and embryos
of the host.
otherwise destined to receive the
Remarks. - As above mentioned, this peculiar parasite was first described
by the present author in his ,,0versigt" under the name of Cryptothiria cypridince.
The description was only a preliminary one, and, after now having subjected
this form to a closer investigation, I am in a position to complete this description,
and at the same time to correct an essential error. The fusiform little creatures
generally found associated with the adult female, firmly anchored to the Cypridina
at one or both sides of the former, are not, as formerly opined, males, but
likewise females, though in a very early stage tf development, having lately
undergone their transformation. The successive stages figured
on PL 97 and
marked 9 1 to 9 6 show this fully. Shortly before the transformation the female
larva burrows its head deeply into the skin of the host (see figs. 9S 9 2
)?
from its anterior part the long, root-like filaments characteristic of the suc-
ceeding stages gradually grow out. Moreover, a highly chitinized reflexed plate,
terminating in several strong denticles, developes from the extremity of the head,
whereby the attachment becomes still firmer (see the figure
and
at the bottom of
the plate on left side). At the same time the fusiform body of the 1st post-
larval stage may be distinctly traced within the larval skin, gradually detracting
itself from the inner walls of the latter, so as at last only to occupy a part of
its inner cavity (see fig.
2
9 )- The empty larval skin is thereupon shed gradually
from behind forwards. In the earliest postlarval stage (see fig. 9 3
) some
of the anterior segments of the larval skin are generally seen still loosely
covering the neck of the young female, with their appendages
in a more or less
complete state; but very soon they too are thrown off. and only the deeply
immerged cephalic segment of the larva remains, constituting the means by
which the female is attached to its host (see fig. 9 4
)- The neck of the latter
now becomes gradually more and more constricted, and at last is converted into
the narrow flexible string by which the female adheres to the host (see figs. 9 5
The form of the body still looks rather different from that of the adult female;
but all intermediate stages may be easily demonstrated by the examination of a
sufficiently rich material. In the interior of the young female a large bag-shaped
body, filled with yellowish contents, may be easily traced. This body, which appears
wholly closed in front, and behind extends into the posterior, narrowly exserted
> 9
6
)-