D’Orbigny’s genus VHliema is founded upon a Doris of this division imperfectly understood.
It requires no great stretch of imagination to convert the spiculous armature of the cloak, in
our species, into a calcareous shield, and the branchial plumes are so very minute, that it is
difficult to recognise their plumose character. M. D’Orbigny describes and figures a circle
of what he calls mamilla (mamelon), corresponding to the plumes in our species, but does not
assign them any function. What he calls the branchiae were probably the ovigerous vesicles
of a small crustacean of the Lernea tribe, which is parasitical on the nudibranchs, and,
burying itself entirely under the skin, shows nothing externally but two ovate processes, that
have the appearance of belonging to the mollusk itself.* Under this view of the subject, the
anomalous characters stated to belong to the supposed genus Villiersia entirely vanish, and
the animal on which it was founded falls naturally into its place among the Dorides.
Doris depressa is generally found adhering to a species of Lepralia, incrusting the under
side of stones in pools, near low-water mark, and so nearly resembles the zoophyte in colour
as not to be detected without a close inspection. This circumstance, with the minute size
and extreme flatness of the animal, may account for its having been so seldom observed,
though the distant localities in which we have found it,—Northumberland and Devonshire,—
show a tolerably wide range of distribution. It must still, however, be considered a rare
species. It is of very sluggish habits, moving seldom and very slowly when in confinement.
We have taken the spawn in September: it is deposited in a slender, depressed thread,
arranged in a delicate, dose, and regular spiral coil of nine or ten volutions; the ova are
placed two or three abreast, and are of a delicate salmon-colour, not much differing from that
of the Leprcdia, on which it and the Dorides are usually found.
Figs. 1, 2. Dojis depressa, different views.
3. A portion of the cloak, showing the tubercles.
4. A tentacle.
5. A branchial plume.
6. Spicula.
7. Spawn.
8. A portion of the same, showing the ova.
* Montagu describes “ two pink oval vesicles” among the branchial papillae on the back of his
Doris ccerulea, which are evidently the ovaries of this little parasite ; and we have ourselves been occasionally
deceived by their occurrence on other species, before we were acquainted with their true
character.
Fam. 1, Plate 12.
Mgs. 9 to 16.
DORIS INCONSPICUA, Alder and Hancock.
D. elliptica, depressa; pallio purpurescenti-albido, punctis minutis fuscis, tuberculisque parvis,
obtusis, omato; tentaculis subrobustis, lamellis compactis; branchiis 10 obtusis, albidis, pinnatiB, anum
haud propinque cingentibus.
Hab. On Cellepora pumicosa, from the deep-water fishing boats, Northumberland, Mr. R. Howse.
Body nearly half an inch long, elliptical, depressed, and nearly equally rounded at both
ends. Cloak of a dull white, tinged with purple, and sprinkled with very minute brown spots:
it is covered with numerous small, obtuse, spiculose tubercles, nearly equal in size. The
spicula of the cloak are rather small and stout; they are more regularly arched than usual,
and are not arranged so regularly as in some of the allied species. Dorsal tentacles rather
large, stout, and nearly linear; the upper portion is pale yellow, with about fourteen compact
laminae, approaching very near to the apex and extending two thirds downwards. The
margins of the cavities are plain, or with only the usual tubercles of the cloak. Branchial
plumes ten, rather small and obtuse, dull white, set in an incomplete circle round the anus,
and at a little distance from it. They are simply pinnate; the pinnae being ten in number,
rather stout and close-set. Head with a broad veil a little undulated at the margin. Foot
elliptic-oblong, slightly bilobed in front, rounded behind, and extending a very little beyond
the cloak when the animal is in motion. The colour is a dull white, with a slight tinge of
yellow in front; the liver appears in a large, broad patch of dark purple through the centre.
This species is closely related to D. pusilla and D. sparsa, but may be readily distinguished
from both by the form of the tentacles and branchial plumes, and from the former,
especially, by the character of the tubercles.
Two individuals were obtained in March, 1848, adhering to Cellepora pumicosa, to which
were also attached two patches of spawn. This is a close, depressed, spiral coil, with the
eggs small, white, and rather numerous.
Figs. 9, 10. Doris inconspicua, different views.
11. A portion of the skin.
12. Tentacles.
13. A branchial plume.
14. Spicula.
15. Spawn.
16. A portion of the same, showing the ova.