24 NOTES ON BOPYRUS SQUILLARUM. 



NOTES ON BOPYRUS SQUILLARUM. 

 A PARASITIC CRUSTACEAN. 



BY W. R. HUGHES, F.L.S. 



Rend hefove the Society, May 31.';/, 1881. 



In lookino over a collection of miscellaneous marine specimens, the 

 proceeds of many a pleasant dredging excursion, which had accumulated 

 during several years, with the view to find some worthy of the 

 museum of this noble college, I found one — the subject of these notes — 

 which I took at Torquay in 1867, and which, as I do not remember to 

 have seen it exhibited here previously, I think may occupy our attention 

 for a few minutes before it follows the example of its fellows. Bopi/rus 

 squillarum is a small parasitic crustacean, of pear-like shape, which 

 selects for its habitat a position beneath the front shield or carapace 

 of the common edible prawn, Pahemon serratiis, and some other 

 allied forms, the presence of the female causing a large tumour of 

 nearly halfan-inch in diameter on the side where the parasite aifixes 

 icself (Fig. 1), the tumour being largest when the parasite is distended 

 with ova. Bopiirua belongs to the second of the two great 

 divisions into which the Crustacea have usually been separated — • 

 the sessile-eyed, that is to say, those whose eyes are not placed upon 

 footstalks, the other division being termed the stalk-eyed. It is of the 

 order Isopoda (equal feet), in which the legs are adapted for walking 

 only, first named by Latreille, and so founded in contradistinction to 

 the order Amphipoda (both feet), the members of which have both 

 swimming and walking feet. 



The family of the Bopyrid.e, which includes Bopijrux squillarum, is 

 small, numbering only four genera, but according to Messrs. Spence 

 Bate and Westwood, the able historians of " The British Sessile-Eyed 

 Crustacea," " it exhibits some of the most remarkable modifications 

 of structure amongst its different members, whilst the characters of 

 the group render it a very distinct one amongst the families of which 

 the order is composed." Limiting for the present a comparison of 

 this singular organism with a high type of the Crustacea — say its host 

 Palcemoji serratux, the common prawn — we shall be able to gain a con- 

 ception of the remarkable modifications which Bopyrus has undergone, 

 if we assume, according to the laws of evolution, that they have both 

 originated from a common progenitor. 



Description of Plate X. 



Fig. 1 gives the Pi-awu and its parasites in situ ; Fig. 2 gives a dorsal 

 view of the female parasite ; Fig. 3 gives a dorsal view of the male para- 

 site ; Fig. 4 gives the male parasite iu the folds of the pleon of the female ; and 

 Fig. 5 gives the naux^lius stage of the i^arasite. Figs. 1, 'I. and -1 are sketched from 

 preserved specimens. Figs. 3 and 5 are copied from " The British Sessile-Eyed 

 Crustacea," by Messi-s. Spence Bate and Westwood.— I am greatly indebted to 

 Miss Hadley for making the illustrations. — W. H. H. 



