688 AUSTRALIAN CRUSTACEAN FAUNA, 



arrest his attention because of the sac-like body — of a yellowish 

 colour — which is to be found attached by a stalk to the sternal 

 aspect of the pleon. This sometimes attracts especial notice, as 

 the parasite is occasionally as large as the body of its host, thereby 

 causing very great inconvenience to the crab when it walks. 

 This parasite is the Sacculina, which forms the subject of the 

 present note. 



Professor Haswell recorded some years ago, in the Proceedings 

 of this Society,* the occurrence of Sacctdina on one of our semi- 

 pelagic species — Xectocarcinus integrifrons — ]>ut, as I shall show, 

 the effect produced in his case is a great deal different from that 

 which I have found in Pilumnopeus serratifrons. In Neclocar- 

 cinus. Prof. Haswell found that only specimens of the male sex 

 were attacked; but in Filu7nnopet(s this state of affairs does not 

 obtain ; instead, I find that the parasite appears to be about 

 equally distributed between the two sexes. 



A very noticeable feature in connection with this SaccuJina is, 

 that out of all the specimens of its host which I examined, none 

 were of a large size. From this one would, of course, infer that 

 it has to a great extent (and to a greater extent as it — the 

 parasite — becomes larger) the effect of arresting any further 

 development of the crab which it has attacked. In one case I 

 found the most unusual occurrence of two specimens of Sacculina 

 having attacked the same individual. They were both of the 

 same size, and were attached side Ijy side. 



Both male and female pleons consist of 7 movable segments, 

 the only difference being that in the female this portion is con- 

 siderably wider than that of the male. 



Quite contrary to my expectations, neither the pleons nor the 

 abdominal appendages of either sex are in any way affected by 

 the parasites. This in itself stamps the pi'esent case as being 

 considei-ably different from that memorable one descriV^ed by Prof. 

 A. Giardf and the before-mentioned case of Nectocarcimis integ- 



t P.L.S.N.S.W. (2), Vol. ii., 1888. 

 J Parasitic castration and its influence upon the male sex in the Decapod 

 Crustacea." Ann. Mag. Nat. Hist. (5), Vol. xix. pp. 325-345, 1SS7. 



