The Relationship of Chaetogaster limnaei (Oligochaeta: Naididae) with a Variety of Gastropod Species

Two subspecies of Chaetogaster limnaei (von Baer) are recognized: C. 1. limnaei (von Baer) inhabits the outer surfaces of its gastropod host and C. 1. vaghini Gruffydd is found in the renal organ (Gruffydd 1965). Many authors have recorded C. 1. limnaei, either in studies of the worm itself or of its relationship with trematode populations, in British species of gastropod in genera such as Acroloxus, Ancylus, Lymnaea, Physa and Planorbis, and in foreign species in genera such as Australorbis, Biomphalaria, Bulinus, Helisoma, Lymnaea, Melanoides, Physa, Physopsis and Segmentina. The subspecies Chaetogaster limnaei vaghini, although not always recognized as such, has been recorded by fewer authors, and only in Lymnaea and Physa (Buse 1968). Observations on Chaetogaster limnaei in the pond at the University College of North Wales, Bangor, in which Lymnaea stagnalis (L.) and L. peregra (Mull.) were the dominant gastropod species, showed that Chaetogaster limnaei vaghini occurred only in the former and C. 1. limnaei solely in the latter. This suggested that the worm might be able to differentiate between various species of gastropod, and it was therefore decided to examine the behavioural relationship of C. limnaei, collected from a wide range of gastropod species, with its host. Setal lengths were also studied, to determine whether any morphological differences were apparent.