Museum AND Art NOTES 121

Natural History Note on Sarsia Mirabilis

By G.- Hi. WaAILES

i

NOTE on the capture of an Oikopleura dioica by Sarsia mirabilis, as witnessed
A at Departure Bay this summer, may be of interest as illustrating the method by

which comparatively rapid swimming organisms may be captured by more
slowly moving jelly fish.

The Sarsia, shown on Plate I., was caught off the wharf at the Biological Station
at Departure Bay on May 6th last; it had its manubrium firmly attached (fig. ID) (eo
the “tail” of an Oikopleura, which was struggling vigorously and dragging the Sarsia
hither and thither in its efforts to escape; they were left thus, and, when again
observed after an interval of nearly an hour, the Oikopleura was packed away in the
manubrium, as shown in fig. 2.

The tentacles of the Sarsia were not seen to come into play during the struggle.

Many larval fishes do not exceed Oikopleura in size and are no more active in
their movements, so that the Sarsia, which often occur in large numbers, may make
considerable inroads on shoals of newly-hatched fish; on the other hand, as the fish
grow larger, they may in turn feed on the Sarsia.

DESCRIPTION OF SARSIA.—Two species of Sarsia are plentiful on the British
Columbia coast, S. flamnea and S. mirabilis; the former has the manubrium attached
to the summit of the bell, in the latter a tubular stalk allows it to hang down below
the bell.

The manubrium contains the gonads or ovaries and a centrally placed stomach,
the opening into which is terminal and provided with incurved lips armed with nema-
tocysts or stinging cells. Fig. 5.

The bell is fairly thick; it is hollow with an internal ring (velum) at the base;
there are four radial canals, each terminating in a tentacle ending in a bunch of small
lobes armed with nematocysts; at the enlarged base of each canal is a black spot
which functions as an eye. The manubrium and bases of the canals are coloured red
in those observed in British Columbia waters, although elsewhere they are reported as
sometimes of a green colour.

Sarsia is the jellyfish stage in the life of a fixed hydroid Syncoryne (Coryne)
mirabilis L. Agassiz (fig. 4), from which minute Sarsia are produced by budding;

these become detached and lead a free-swimming life, growing to nearly half an inch
in height of bell.