A MESS-MATE OF LIMN^A STAGNALIS. 



By GEORGE BAILEY, F.R.M.S. 



Some time ago I had a number of Liiinuca siagiialis put into a bell- 

 glass and kept alive for purposes of obser\ation. They were 

 obtained from a small, obscure, pond south of Croydon, in Surrey. 

 The only special features noticeable about the shells were their 

 more than usually eroded condition, and the distinct white mark on 

 the last whorl near the columella. The molluscs in confinement 

 were very active. This seemed the more remarkable because 

 they were infested about the head and mantle with what appeared 

 to the naked eye like parasites. The Limnaea;, however, gave no 

 signs of discomfort, in spite of the host of " hangers on." 



When detached and obser\ed under a i inch objective, the 

 appearance and form of these bodies resembled worms ; and they 

 moved after the manner of leeches, by attaching themselves to 

 the glass cells, and did not attempt in any way to swim freely. 

 On examining one of them under a \ inch objective, it soon 

 became evident that the subject of inquiry was a naid worm. 



One species of naid is said to have parasitic tendencies, 

 attaching itself usually to Liininra, and feeding on animalcules. 

 Manifestly the example under consideration was living as a 

 commensal with Lmna;a stagndis ; and it answers fairly well to 

 the description of Chatogasfey vcymiculans given by Claparede, 

 Grube, and others. Johnston, in his " Catalogue of Annelids," 

 describes the genus Cludogaster — '-' Body cylindrical, truncate in 

 front, eyes none, mouth terminal, barbed underneath, bristles all 

 forked spineti." Various synonyms are used by different authors, 

 evidently describing the same worm— ^.^., Nnis veymiculavis, Nais 

 diaphana, Chcetogastcy limn.va, Chxtogastey diaphana, and Chatogaster 

 venniciilai'is. 



