A phylogenetic analysis of Tubificinae and Limnodriloidinae (Annelida, Clitellata, Tubificidae) using sperm and somatic characters

The spermatozoa and the sperm aggregates of 13 species belonging to four genera ( Smithsonidrilus,Limnodriloides, Thalassodrilides, Doliodrilus ) in the tubificid subfamily Limnodriloidinae (Annelida, Oligochaeta) were studied and compared with the spermatozoal patterns already described in the subfamily Tubificinae. Two characters considered exclusive for the Tubificinae were found in the more spermatologically variable Limnodriloidinae: the production of two kinds of spermatozoa, eusperm and parasperm, and the presence, in the spermathecae, of sperm aggregates formed by a combination of the two sperm types. A parsimony analysis was performed on the spermatozoal data of the species examined and compared with that based on the somatic characters of the same species: a critical revision of the already codified eusperm characters was carried out and the ultrastructure of parasperm was used as a new subset of spermatozoal characters. In a total evidence approach, a further parsimony analysis was run using a matrix combining both sets of characters. This analysis suggested that the double sperm line and the sperm aggregates composed of both eusperm and parasperm may well be homologous in tubificines and limnodriloidines. It thus supported the previous notion that Tubificinae and Limnodriloidinae are closely related and indicated that these subfamilies may be sister taxa.