Orbitestellidae, Iredale, 1917

Hawe, Andreas & Haszprunar, Gerhard, 2014, 3 D-microanatomy and histology of the hydrothermal vent gastropod Lurifax vitreus Warén & Bouchet, 2001 (Heterobranchia: Orbitestellidae) and comparisons with Ectobranchia, Organisms Diversity & Evolution (New York, N. Y.) 14 (1), pp. 43-55 : 53

Placement of Orbitestellidae among basal Heterobranchia

The phylogenetic tree of the basal, non-euthyneuran Heterobranchia is still doubtful. There is general agreement that these “ Heterostropha ” Fischer, 1885 or “ Allogastropoda ” Haszprunar, 1985 are “a paraphyletic holding vessel for problematic taxa” ( Bieler 1992:326) currently including Ectobranchia ( Valvatoidea ), Orbitestellidae, Architectonicoidea ( Mathildidae , Architectonicidae , Omalogyridae : Haszprunar 1985 a, 1988), Murchisonellidae ( Ebalidae ), Aclididae ( Aclis , Graphis and Larochella ), Cimidae , Rhodopemorpha ( Rhodope and Helminthope ), Tjaernoeidae , Rissoellidae , and Acteonoidea, whereas (contrary to previous ideas) the Pyramidelloidea ( Amathinidae , Pyramidellidae ) are to be placed among the Euthyneura ( Jörger et al. 2010; Wilson et al. 2010; Dinapoli and Klussmann-Kolb 2010; Dinapoli et al. 2011; Göbbeler and Klussmann-Kolb 2011; Schrödl et al. 2011).

Due to various morphological similarities, Ponder (1990a, b) classified the Orbitestellidae within the Ectobranchia —a view also supported by sperm fine structure ( Healy 1990, 1993). However, already Ponder (1990a: 527) remarked that the characters shared by Orbitestellidae and Valvatidae are “probably plesiomorphic” (for Heterobranchia) and later on ( Ponder 1991:22) considered Orbitestellidae as “rather distantly related to Cornirostridae and Valvatidae ”. Bieler et al. (1998: 318) again noted remarkable differences between the Orbitestellidae and the remaining taxa in “…the still illdefined Valvatoidea ”. Recent molecular analyses always show the Orbitestellidae separated from the Ectobranchia (e.g. Dinapoli and Klussmann-Kolb 2010; Jörger et al. 2010; Schrödl et al. 2011) and our anatomical data support this view. Similarities between Ectobranchia and Orbitestellidae such as the pallial tentacle, the pallially located kidney, the lack of radular cartilages, the long and tubular salivary glands, the gastric shield or sperm details ( Healy 1990, 1993) are all plesiomorphies of Heterobranchia, whereas the shared copulatory organ is considered as analogy due to different innervation (cerebral in Ectobranchia , pedal in Orbitestellidae ). Moreover, Orbitestellidae share apomorphic characters with non-ectobranch Heterobranchia, namely the presence of opponent ciliary tracts. We conclude that Orbitestellidae cannot be included in Ectobranchia , but is an early heterobranch offshoot proper and that Ectobranchia is confirmed as the first subclade of Heterobranchia ( Haszprunar et al. 2011; Brenzinger et al. 2013a, b).

Further phylogenetic assumptions and the degree of relationship to the remaining taxa of non-euthyneuran Heterobranchia (see above) will require careful analysis of morphology and molecules. The story will continue.