Microanatomy of shelled Koloonella cf. minutissima (Laseron, 1951) (Gastropoda: 'lower' Heterobranchia: Murchisonellidae) does not contradict a sister-group relationship with enigmatic Rhodopemorpha slugs
Brenzinger, B.; Wilson, N.G.; Schrödl, M. (2014). Microanatomy of shelled Koloonella cf. minutissima (Laseron, 1951) (Gastropoda: 'lower' Heterobranchia: Murchisonellidae) does not contradict a sister-group relationship with enigmatic Rhodopemorpha slugs. J. Moll. Stud. 80(5): 518-540. dx.doi.org/10.1093/mollus/eyu036
In: Journal of Molluscan Studies. Oxford University Press: Reading. ISSN 0260-1230; e-ISSN 1464-3766, meer
The Murchisonellidae are a small taxon of minute snails with a high-spired shell that occur in shallow marine habitats. Molecular phylogenetics recently revealed that they are not members of the externally similar yet phylogenetically derived Pyramidellidae, but instead potentially one of the oldest clades among the heterobranch Gastropoda. Furthermore, current data surprisingly indicate a sister-group relationship with Rhodopemorpha, highly aberrant marine slugs with previously unclear affinities. Murchisonellidae are characterized by a specialized pincer-like radula, but very little further data exist on soft-body anatomy for most species, and there are only a few observations of living animals. Investigation of the anatomy of Murchisonellidae may thus yield new data providing insights into early heterobranch evolution and that of enigmatic Rhodopemorpha. We collected live specimens of the murchisonellid Koloonella cf. minutissima ( Laseron, 1951), a member of a genus known mainly from eastern Australia. We provide detailed live photographs and interactive 3D data on all major organ systems, based on serial histological sections. The mantle cavity is shown to contain several distinct glands, a pair of which is conspicuously similar to glands found in Rhodopemorpha. The anterior digestive system contains a unique four-toothed radula, a feeble pharynx and a special, vacuolated oesophageal bulb. The reproductive system is complex and diaulic, and contains unusual structures. These results highlight structural diversity among minute lower Heterobranchia. Soft-body characters do not contradict, and may even support, the counterintuitive sister-group relationship with shell-less, wormshaped Rhodopemorpha. The classification of Murchisonellidae is discussed and a revised scheme is proposed.
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