] 49 [ 
II. On Splanchnotrophus, an undescribed Genus of Crustacea, parasitic in Nudi- 
branchiate Mollusca. By ALBANY HANCOCK, F.L.S., and the Rev. ALFRED MERLE 
Norman, M.A. 
(Plates XV. & XVI.) 
Read November 6th, 1862. 
IN the < Monograph of the British Nudibranchiate Mollusca,” Messrs. Alder and Han- 
cock briefly described and figured three or four new forms of Entomostraca which had 
been found infesting the Nudibranchs. This was done partly to illustrate the history of 
these beautiful Mollusca, but mainly with the view of directing the attention of those 
naturalists who might be interested in the subject to the parasites. It was therefore 
unnecessary on that occasion to go into much detail; and, indeed, the material then at 
disposal was too limited to enable this to be done. Recently, however, Mr. Hancock has 
obtained a fresh supply of specimens of two of the forms ; and as their characters are very 
abnormal, and consequently possess much interest to the systematist, we propose to give 
in this communication as complete a description of them as we are able—though this 
description must still be imperfect in many anatomical details, since the number of 
specimens even now at our command is not great. 
The species which occurred in Doris tuberculata, figured plate 45. fig. 10, as well as 
that which was taken on Antiopa cristata, were referred in the monograph to Ergasilus. 
Leydig has, however, constituted a genus under the name of Doridicola *, to which these 
parasites would appear more properly to belong. We hope, however, hereafter to have 
the opportunity of giving a more detailed account of these animals, which are active 
little beings, and have been observed flitting about from place to place on the surface 
of the infested animals, or resting and anchoring themselves by their long prehensile 
antenne amidst the gills of Doris or the papille of Eolis, there, no doubt, to seek their 
required nourishment. 
It is not, however, with such neat, agile, and sprightly forms that we have to do on 
the present occasion. The creatures which now claim our attention are ill-formed and 
monstrous-looking; they live constantly attached to one place, and are almost motionless. 
Two species of these curious animals have occurred. Both are internal parasites, lying 
buried within the visceral chamber of their victims. The minute caudal extremity and 
the ovigerous sacs of the female, however, appear at the surface. i 
The one species was obtained in Doris pilosa from the coast of Devonshire, and has 
since also occurred in Idalia aspersa, taken on the west coast of Ireland, either at the 
Isles of Arran or Birterbury Bay. The other species has been found in Eolis rufibranchi- 
alis and Doto coronata, captured on the shores of Northumberland. Mr. H. T. Mennell 
and Mr. Hancock found three individuals of the latter species in April of last year, which 
* Leydig, “ Neuer Schmarotzerkrebs auf einem Weichthier," Zeitschr. f. wiss. Zool. vol. iv. (1853) pp. 377-382. 
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VOL. XXIV. 
