Systematic Zoology

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Ph.D. Thesis

PhD Thesis working title: "Anatomy and phylogeny of basal heterobranch molluscs"

The heterobranch molluscs are the monophyletic aggregation of all higher gastropods including the presumably non-monophyletic opisthobranch and pulmonate taxa (Dinapoli & Klussmann-Kolb 2010). In particular the phylogeny of the basal taxa is uncertain although some bigger species like Valvata piscinalis are known and well reviewed in anatomical details for over a century (e.g. Bernard 1888, Garnault 1890).
In the 1980s and 1990s there was an exhaustive number of new described species, mostly by their shell, radula and soft body morphology (Bieler et al. 1998, Hasegawa 1997, Marshall 1988, Warén 1991, 1992, 1993, Warén & Bouchet 1989, 1993, Warén et al. 1993, 1997). A detailed anatomical description, however, was missing in most cases.

Anatomic characters therefore are of central importance to a) ascertain phylogeny and b) characterize a hypothetical ancestor of all heterobranch molluscs. Two problems appear: most newfound species are of a helicoid form and relatively small (about 1-3 mm), therefore an anatomical characterization was nearly impossible. A phylogenetic analysis with the help of morphological characters was mostly based on shell and radula descriptions – thus a misclassification of such species is a common rule.

In years of molecular and genetical approaches within systematics, morphological solutions were mostly repelled. In the ongoing discussion there was an accelerating argumentation on the basis of molecular data (e.g. Dinapoli & Klussmann-Kolb 2010). Morphological approaches and associated mechanisms of ecology and behaviour were more or less ignored.

In contrast, modern methods of slicing and computer-aided 3D-surface rendering demonstrate a solution to achieve qualitatively first-class and concrete results in microgastropod anatomy. A deduction of ecology and behaviour is also given within these techniques to a certain extend. This fact emphasizes the significance of morphological solutions, not least because most species are deep-sea forms whose reproduction biology and ecology is mostly unknown. In addition some forms are hot-vent dwellers, a habitat yet with some mystical character.

3D-rendering is a proper and interactive way to capture, visualize and analyze the inner anatomy of microgastropodes. With the help of these techniques it was possible to entirely reconstruct the more or less confusing digestive and genital systems. A reclassification within ectobranch molluscs was possible.

In the future, these techniques shall be used for more species and higher taxa. We intend a morphological approach to achieve a new phylogenetic system for all basal heterobranchs.