PROCEEDINGS 
OF THE 
Cambridge Philosophical Society. 
\Thompsonia,a little known Crustacean Parasite. (Preliminary Note.) 
| By F. A. Ports, M.A., Trinity Hall. 
[Read 4 May 1914.] 
Thompsoma is a genus of Cirripedia belonging to the parasitic 
family the Rhizocephala, and was first noted by Kossmann* in 
11874 as a parasite upon the small crab Melia tesselata from the 
Philippines. Since that time it has been described by Coutieret 
junder the name of Thylacoplethus as a parasite of Alpheids in Kast 
Indian and Australian waters, and by Hafelet and Kruger§ from 
the crab Pilumnus and the hermit crab ELupagurus middendorfiu 
lott the coasts of Japan. I have little hesitation in including all 
lthese forms in the same genus, even though Thompsonia thus 
enjoys a far greater diversity of hosts than any other Rhizocephalan, 
/for as a rule each genus is strictly confined to the same subdivision 
jof the Decapoda. In 1913 I accompanied the expedition of the 
\Carnegie Institution of Washington to Torres Straits at the kind 
linvitation of Dr A. G. Mayer, and during a short stay at Murray 
Asland I collected nearly twenty individuals of a species of 
Synalpheus, commensal with the crinoid Comatula parvicirra, 
\infected by a parasite which is clearly identical with Coutiére’s 
genus Thylacoplethus. I also obtained a specimen of the swimming 
* Arb. Zoot. Inst., Wiirzburg, Bd. 1. p. 97, 1874. 
+ C. R. Acad. Sci. Paris, T. cxxxiv. pp. 913 and 1452, 1902, 
+ Abh. Akad. Miinchen, 2 Suppl. Bd. 7 Abh, 1911. 
§ loc. cit. 2 Suppl. Bd, 8 Abh. 1912. 
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