Dr. F. Miiller on a new Parasitic Isopod Crustacean. 87 



IX. — On Entoniscus Porcellanee, a new Parasitic Isopod Crusta- 

 cean, By Dr. Fritz Muller, of Desterro*. 



[Plate II. figs. 8-16.] 



The genus Bopyrus has hitherto passed as the extreme member 

 of the series of Isopod Crustacea, stunted in development by a 

 parasitic existence. Much further removed from the mode of 

 life and structure of the free Isopods, and from its own youthful 

 form, is a parasite of the same Porcellana round the intestine 

 of which Lernceodiscus twines its roots, and in the branchial 

 cavity of which, it may be remarked, in passing, a Bopyrus not 

 unfrequently takes up its abode. 



The female of this parasite lies in a thin-walled sac between 

 the liver, intestine, and heart of the host; its head has lost both 

 eyes and antennae, and taken the stomach up into itself; the 

 thorax has become an irregular inarticulate sac beset with enor- 

 mous brood-laminae ; the long, vermiform, and extremely mobile 

 abdomen has sword-shaped legs ; and, swelling out above it in a 

 globular form, as if in a hernial sac, the heart lies at the base of 

 its first segment ! 



As the first-known internally parasitic Isopod, I have given 

 the animal the name of Entoniscus Porcellanee. 



The female (PL II. fig. 8) attains a length of from 10 to 15 milli- 

 metres. The head forms a whitish, soft, roundish mass, about 

 1 millim. in length and 1*5 millim. broad. Above, it is divided 

 somewhat like a brain, by a shallow longitudinal furrow, into 

 two convex halves, between which a short rounded lobe springs 

 before and behind. A little before the middle of the rather flat 

 under surface, the mouth is seen, in the form of a minute longi- 

 tudinal fissure; and around this are various lines, probably indica- 

 tions of oral organs which were more distinct at an earlier period. 

 The resemblance of the head to a brain is further heightened by 

 irregular furrows which pass through it, giving it the appearance 

 of convolutions. If the outer skin be torn to pieces, these are 

 found to be due to numerous conical caeca, to the fatty contents 

 of which the head is indebted for its white colour, and which 

 may correspond with the caeca described as the liver on the an- 

 terior part of the intestine of Bopyrus. Antennae and eyes are 

 not to be found in mature females; in a younger specimen I 

 once saw a pair of short thick processes above the single lower 

 lobe, which were probably remains of antennae. 



Bending upwards, the head forms an obtuse angle with the 

 thorax, and is capable only of an inconsiderable vertical movement. 

 The long, sacciform, inarticulate thorax appeal's to be quite shape- 



* Translated from Wiegmami's Archiv, 1862, by W. S. Dallas, F.L.S. 



