Helicarionidae, Bourguignat, 1877

Hyman, Isabel T. & Ponder, Winston F., 2010, A morphological phylogenetic analysis and generic revision of Australian Helicarionidae (Gastropoda: Pulmonata: Stylommatophora), and an assessment of the relationships of the family 2462, Zootaxa 2462 (1), pp. 1-148 : 7-8

Relationships of Helicarionidae and Limacoidea sensu lato

As outlined above, the relationships within Helicarionidae and Limacoidea s. l. are still far from resolved. There is little resolution at even a superfamilial level, regarding the taxonomic position of these groups with respect to other land snails ( Hausdorf 1998; Table 1). Early classifications based on the Pilsbry-Baker system ( Baker 1955; Pilsbry 1900), such as those by Baker (1941a), Solem (1978) and Boss (1982), place Helicarionidae s.l. (including Helicarioninae, Dyakiinae, Ariophantinae , Urocyclinae , Euconulinae ) in the superfamily Limacoidea (=Limacacea) with taxa such as Zonitidae (including Trochomorphidae , Vitrinidae , Vitreidae , Gastrodontidae ) and Limacidae (including Milacidae , Agriolimacidae ). In Solem’s (1978) classification, Limacacea is grouped with Arionacea and Succineacea in the suborder Aulacopoda .

Schileyko (1979) presented a contrasting classification based on his consideration of shell and reproductive characters, but not resulting from an explicit phylogenetic hypothesis. He placed some of the taxa traditionally included in Limacoidea in the suborder Helixina ( Helicarionidae , Ariophantidae , Urocyclidae , Trochomorphidae , Euconulidae , Vitrinidae , Zonitidae ), along with a large number of other taxa (e.g., Helicoidea , Endodontoidea, Arionoidea), while other limacoidean (sensu lato) taxa were placed in the suborder Limaxina ( Limacidae , Trigonochlamydidae ). Thus the broad limacoidean group of Baker (1941a) and Solem (1978) was broken up. However, in Schileyko’s more recent classification (2002a,b, 2003a,b) the limacoidean taxa were brought back into the same suborder and infraorder (Limacoidei, Limacoinei), but other superfamilies were also included (e.g., Camaenoidea), indicating that the Baker / Solem concept of Limacoidea s. l. was not necessarily regarded as monophyletic. Again this was not based on an explicit phylogenetic hypothesis.

Nordsieck (1985, 1986) produced a classification based on the excretory system, reproductive system and shell, which was slightly modified following a phylogenetic analysis ( Nordsieck 1993). He divided most of the Limacoidea s. l. taxa into Helicarionoidea , Zonitoidea and Limacoidea , grouping them with Helicoidea and Arionoidea in Arionoinei, indicating that Limacoidea s. l. is not monophyletic.

An alternative classification produced by Tillier (1989) placed Helicarionidae (including Ariophantidae and Urocyclidae ) in the superfamily Helicoidea , but grouped Euconulidae , Trochomorphidae and Limacidae with Zonitidae and Arionidae in the superfamily Zonitoidea , again breaking up Limacoidea s. l. . Tillier’s classification was based on a phylogenetic analysis that used characters from the excretory, digestive and nervous systems. The reproductive system, which is the most important source of characters in other classifications, was not studied. The characters that were included had almost as much variability between families as they did within families ( Tillier 1989). In addition, Tillier used an algorithm that did not allow reversals. For these reasons his classification was considered seriously flawed ( Hausdorf 1998), although it remains an interesting contrast to the phylogenies in which reproductive characters dominate.

Hausdorf’s (1998) phylogenetic analysis of Limacoidea s. l. demonstrated monophyly but only used members of Helicoidea as outgroup taxa. The only phylogenetic analysis of Limacoidea s. l. based on molecular data ( Wade et al. 2001, Wade et al. 2006) also showed the group to be monophyletic with Arionoidea as the sister group.

The existing classifications outlined above are significantly different. One reason for this may be the different data sets used by different authors and the characters that they considered to be important phylogenetic markers. For example, the excretory system was considered to be very important by Solem (1978), Nordsieck (1985, 1986) and Tillier (1989), but was not used by Schileyko (1979, 2002a,b, 2003a) or Hausdorf (1998). Tillier (1989) did not use the reproductive system, which was the most important character source in the other classifications. Other factors may be the interpretation of characters, which resulted in different assumptions about homology, and the different analytical techniques used (e.g., Emberton et al. 1990).