THE ISOPOD GENUS ICHTHYOXENUS HERKLOTS, WITH 

 DESCRIPTION OF A NEW SPECIES FROM JAPAN. 



By Harriet Richardson, 



Collaborator, Division of Marine Invertebrates, United States National Museum. 



In 1870 Herklots ^ described the type-species of the genus IcMhyo- 

 xenus which was found parasitic on the fish Barhodes maculatus 

 Bleeker from Java. The mode of life of this isopod is pecuhar and 

 interesting. It bores a hole in the body of the fish just back of the 

 lateral fin, where it fives with its mate. It enters this cavity when 

 young. As it grows m size, it is unable to leave the body of the fish 

 and becomes many times larger than the opening through which 

 it entered. This species was named after Mr. Jellmghaus, who was 

 the first to notice the parasite, which he called '^songkeat," and who 

 in 1860 wrote a note concerning it to the Societe physique des Indes 

 neerlandaises.^ The fish was taken from the River Tjikerang, 

 district of Tjilokotot, regency of Bandong. 



The second species of the genus, Ichthyoxenus montanus, was 

 described by Schicedte and Memert^ in 1884. It was found on Puntius 

 sopJiores in the Himalayan Mountains. 



Up to the present time these two were the only species known. 



In 1908 Maj. P. A. Ouwens * mentioned another host for Ichthyo- 

 xenus jellinghausii, the fish Nemacheilus fasciatus van Hasselt, from 

 the Tji-Seroema near Batavia. 



Not long ago Dr. Harold Heath wrote to me concerning some 

 parasites which were found on Japanese fishes from Lake Biwa. 

 They were described as living in the body of the fish, which they 

 entered through a hole bored just back of the lateral fin. The 

 specimens were sent to the United States National Museum by Mr. 

 Will Thompson, and the parasites proved to be a new species of 

 Ichthyoxenus. The hosts are Acheilognathus rhombeum (Schlegel), 



1 Archives Nderlandaises des Sciences, vol. 5, 1S70, pp. 128-137, pi. 5, figs. 10-18. 



sNatuurk. Tijdschr. Nederl.-Indie, vol. 22, 18G0, p. 378. 



3 Nat. Tidsskrift (3), vol. 14, 18S4, pp. 303-309, pi. 11, flgs. 10-11. 



*Natuurk. Tijdschr. Nederl.-Indie, vol. 67, 1908, pp. 29-35. 



Proceedings U. S. National Museum, Vol. 45— No. 1995. 



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