download pdf

218
The genus MiCrOmSCUS, Fritz Miiller.
(See PI. XCII).
In the year 1870 Fritz Miiller examined a small Isopod found by him
parasitic on a Copepod (Calanoid) from Brazil, and described it under the name
of Microniscus fuscus as the type of a new genus of Bopyridse. Some years
afterwards I found a similar form off the Lofoten Islands clinging to a calanus
finmarchicus, and I recorded it briefly in my ,,0versigt" as a new species under
the name of Microniscus calani, though at the same time expressing my doubt as
to its being an adult animal somewhat in the following terms: ,,I feel, however,
great doubts as to the validity of the genus Microniscus, for both the form
described by Fritz Miiller and that examined by myself, exhibit so strong a re-
semblance to larval stages of other Epicarida, that I should be much inclined to
believe that both these forms represent immature animals, which would never
have reached to sexual maturity in the hosts on which they were found." On
re-examining the material of Microntsci subsequently collected, I am now in a
position to give full proof of the correctness of the above-quoted supposition.
The genus Microniscus, which is even regarded by MM. Giard and Bonnier as
the type of a distinct family, must indeed be altogether discarded, as only re-
presenting a transitory larval stage of Epicarida belonging
to different families.
In the several forms of Epicarida only 2 larval stages have hitherto been de-
scribed, and these 2 stages are so very different both as to the general form of
the body and the structure of the several appendages, that it is rather difficult
to imagine how the one could develop from the other. Nor,
so far as
I know, has the immediate transformation of the one stage into the other ever
been observed by any zoologist. Now the observations which I have had an
opportunity of instituting, and of which the results are elucidated by the figures
given on PI. 92, make it highly probable, that in all Epicarida there exists an
intermediate larval stage between the 2 formerly observed, and that this stage is
actually the Microniscus. Whether this stage in all cases is parasitic on Cope-
poda, I cannot say with certainty; but for 2 different forms at least, evidently
belonging to 2 different families, the parasitism on Copepoda is now proved.
In one place on the west coast of Norway (Eggesb0nses), a Mimni'i*