131
THE OCCURRENCE OF CERIANTHUS IN
THE PLANKTON OFF SOUTHEND.
By F. J. LAMBERT.
(With One Plate.)
ON the 3rd June, 1938, while using a surface drift-net,
16 inches in diameter, amongst other material I obtained
four larvae of a coelenterate which, having no reference-books
by me, nonplussed me completely.
The larvae were from 2 to 3 mm. in length, frosty-transparent,
in appearance something between a medusoid and an anemone.
They were not all identical and were possibly in different stages
of development. They remained floating constantly within
three inches of the surface in the cell within which I had placed
them, with the tentacles downward, and moved only by ciliary
action. In the two largest specimens there were two circular
groups of what appeared to me, under a pocket-lens, to be gastric
cirrhi. much resembling in appearance those organs in Aurellia.
They appeared just above the tentacles at opposite sides of the
column, or bell, in the upper part of which appeared a body, oval
in appearance, filling its upper part. In the two smaller speci-
mens it was circular and smaller. It seemed to me that the
function of this body was to act as a " float," and if so this would
account for the constant position of the creature at one particular
depth in the water.
The tentacles, which varied in number in different specimens,
also varied both in size and appearance; some were long and
well-developed, others mere knobs: they had no power of
protrusion or retraction, and only very little reaction to stimulus,
and then only at the tips. I found it difficult, under an inch
objective, to be sure of their number owing to this variability,
but considered them as ranging from eight to thirteen.
The mouth appeared to consist of two raised processes as
large as, and of the same appearance as, some of the tentacles.
I failed to induce them to feed either on particles of the clitellum
of earthworm or on newly released nauplii of Artemia; two of
them, dropped into a jar of swarming Artemias, were removed a
few hours later looking very sickly: there was no evidence of
any food having been taken.