IDALIA ELEGANS.
which his description was taken, however, was not half the size of ours, and appears to have
been less brightly coloured; the branchial plumes were also proportionally smaller, which may
have arisen from its being a young individual. We think that we likewise recognise in our
animal the true Idalia elegans of Leuckart; although his description, having been taken from a
dead specimen, is deficient in some of the points necessary for comparison. The characters
agree in every thing as far as they go. The number of branchial plumes is greater in this than
in any other species of the genus. Leuckart makes them, 18-20,’ and according to our own
observation the real number is eighteen, though from two of them being bifid, they exhibit
twenty points. One or two of the posterior ones are very inconspicuous, and may readily be
overlooked.
Well indeed does this Idalia merit the name of elegans! It is certainly the most beautiful
of the tribe we have met with. The orange of the filaments is so brilliant as to defy the power
of the painter, and the delicate rose-colour of the body, in the individual from which our
drawing was taken, added much to its attractions. A second specimen had the colours a
little darker.
This valuable addition to our Fauna was dredged in the summer of 1853, near Castle
Comet, in Guernsey. From a curious habit, hitherto unknown in this tribe, of concealing itself
in the test of an Ascidian (Cynthia tuberosa), it escaped observation on being taken from the
dredge, and was put into our collecting-box as an Actinia partially expanded. On examining
the contents of the box in the evening, we were delighted to find we had got a beautiful Idalia.
which had crept so far out of its place of concealment as to display its true form. A second
individual was afterwards found amongst the contents of the box, with only its head and
anterior filaments protruded from the test of another Cynthia of the same species. This was
put into a glass of sea-water over night untouched, to allow it to creep out without injury: but
in the morning it was found inhabiting the same cavity, from which it had not made any
attempt to escape, and it required a gentle pressure of the Ascidian to disengage it. From
our desire to get a drawing of the Nudibranch in a fresh state, we neglected to examine the
Ascidian more carefully, in order to ascertain the nature of the connexion between them.
The cavity from which it emerged appeared to be similar to those made by the Modiola
marmorata, which is frequently lodged in the test of this Cynthia, and the Idalia may therefore
have entered it to prey upon the mussel; but it is a curious circumstance that both the
specimens taken should have been so lodged, and with the head outwards; seemingly indicating
a habit of remaining concealed in such a situation, which the reluctance to quit it also
seemed to imply.
Figs. 1, 2. Side and back views of Idalia elegans.
3. Two brachial plumes, much enlarged.
4. Front view of tentacle.
Mg. 5.
IDALIA LEACHII, Alder and Hancock.
I. alba; tentaculis gracilibus; ihargine palliali filamentibus perlongis, anticis 4, lateribus utrinque
6, instructo; filamentibus dorsalibus numerosis, ordinibus 3 vel 5 ; branchiis 11, pinnatis, insequalibus.
Idalia elegans, “ Leuck,” Alder, in Trans. Tynes. Club., p. 112.
Hab. Torbay, Mrs. Griffiths, (Mus. Leach). 'Whitburn, Durham, Rev. G. Cooper Abbes.
Hebrides, G. Barlee, Esq.
Body about an inch long, convex, white tinged with rose-colour from the viscera shining
through. Tentacles linear, tapering, long and slender, finely laminated posteriorly nearly to
their base; with four filaments in front, two near the base of each tentacle, set on the pallial
margin, which passes close in front of the tentacles, and circumscribes a small area on the back.
Lateral filaments six on each side, long and slender, the last bifid; attached to the pallial
ridge. There are numerous filaments on the back; the central row containing three, and the
two sublateral rows three or four filaments each: there are occasionally two additional rows
developed posteriorly, containing one. or two filaments each; making in all five rows.
Branch/ice consisting of eleven slender pinnate plumes, largest in front and becoming small
behind, where the circle is incomplete. The anterior plume is bifid for about two thirds the
length: the two posterior plumes are also bifid. Foot broad and fleshy, tapering to an obtuse
point posteriorly.
The spicula are large, linear-fusiform and more or less bent in the centre, around which
they are strongly nodulous: one or two rings of small nodules occur also on other parts of
the surface.
We described this species under the name of Idalia elegans in the Catalogue of the
Mollusca of Northumberland and Durham, on the authority of a specimen so named in
Dr. Leach’s Collection in the British Museum, expressing, at the same time, a doubt of the
correctness of the appellation. Further observation has convinced us that this is not the
species of Leuckart; and having recently taken specimens of what we think to be the true
Idalia elegans, we have given the name of Leachii to the animal now under consideration. It
comes very near to the I. cirrigera of Phillippi, from which, however, it differs in the number
of filaments and branchial plumes. Dr. Phillippi’s figure also represents the dorsal area
much broader than it is in our animal.
Fpur examples of this fine Idalia have occurred:—the British Museum specimen already
mentioned, sent from Torbay by Mrs. Griffiths; a small individual, half an inch long, obtained
by Mr. Abbes from the fishing-boats at Whitburn; and two specimens got by Mr. Barlee in
one of his dredging excursions to the Hebrides, which are now, by his liberality, in our
possession. The Whitburn Specimen, the only one we- have seen in a fresh state, and from
which our figure is taken, was unfortunately dead when it reached us. The drawing is,
consequently, less perfect than it might have been had we seen the species alive.