The only classification problem with modern monoplacophorans is the discussion around using Monoplacophora
Odhner, 1940 vs. Tryblidiida
sl. as defined in Runnegar & Jell (1976) would include three orders among which Tryblidiida
. Problems arise from the ambiguous position of some paleozoic fossil taxa which could be monoplacophorans or gastropods, or (worse) stem-group gastropods derived from monoplacophorans, thus making Monoplacophora
paraphyletic. Preference for the name Tryblidiida
follows Waller's (1998) conclusion that these are the sister-group to all other Conchifera
, thus escaping being paraphyletic. Giribet et al. (2006: Proceedings of the National Academy of Sciences 103, 7723-7728) claimed that the monoplacophoran Laevipilina
is recovered within a branch containing polyplacophoran taxa in an analysis including several nuclear and mitochondrial sequences. As mentioned above, this result based on a very small specimen is ignored in the classification draft until further confirmed.