DENDRONOTUS ARBORESCENS.
There are six or seven pairs diminishing in size towards the tail, which does not extend far.
beyond them. In fine old specimens there are also smaller intermediate tufts. The anterior
pairs have four or five principal branches, which are divided and subdivided into numerous
delicate points. The posterior ones are less branched. Foot very narrow, linear, rounded
in front, the sides thin, and adapted for clasping. The heart forms a large swelling between
the first and second pairs of branchial tufts. It pulsates about seventy-six times in a minute.
The eyes are placed on the sides a little below the tentacular sheaths, and are very small.
The young are very pale, and the spots exceedingly delicate: in this state the digestive
system is distinctly seen extending nearly the whole length of the body, and giving off
branches into the arborescent tufts and tentacles.
When fully developed this is' a splendid animal. It is subject to much variation in
colour, which has given rise to some spurious species. Occasionally we have met with an
individual perfectly white and transparent, showing the coloured viscera within. This we
take to be the Tritonia lactea of Mr. Thompson. Another beautiful variety, which we
formerly described under the name of Trit. pulchella, is much smaller, and of a uniform
pale rose-pink, with yellow tubercles. The T rit.fe lin a , also described by us in the 'Annals
of Natural History,’ may possibly be another variety, but as there are some little differences
of form and consistence, we prefer keeping it apart at present.
These molluscs crawl but slowly on a plain surface, but on corallines they move with
graceful facility, their tree-like plumes waving at every turn. Frequently, clasping the
coralline with only a small portion of the foot, they will remain suspended by it, moving their
bodies about in all directions.
Dr. Grant has given a curious account of sounds emitted by these animals, which he
conceives to proceed from the action of the jaws. Though we have frequently kept them
alive for several days together, we could never succeed in detecting any sound. It may possibly
only be produced under peculiar circumstances.
Dendronotus arborescens appears to have a wide range in the northern seas, extending
from Greenland to the shores of the English channel; and it is again met with on the northeast
coast of America.
Its spawn is deposited in the spring months, at which period large individuals may usually
be found among the rocks between tide marks. The young, however, occur all the year
round. The spawn is of a pale yellow or rosy colour, and is about twice coiled ; the ova are
arranged in a small cord doubling upon itself as in the spawn of Eolis papillosa, which this
greatly resembles, but is ndt quite so large.
Eig. 1. D. arborescens, usual appearance.
2. Light red variety.
3. White variety, (!Tritonia lactea, Thomp.)
(The figures in this Plate have been inadvertently reversed.)