Systematics, reproductive biology and biogeography of viviparous marine Planaxidae (Mollusca, Gastropoda)

Salt determines live birth or larval stage

Poecilogony refers to a reproductive pattern within a species with two distinctly different reproductive strategies. This pattern is mainly found in Ophistobranchia, but has also been proposed for other snail species, although it has not been confirmed in most cases.

We revisit poecilogony for the marine gastropod Planaxis sulcatus (Born, 1780): Previous studies focussed on the two modes of reproduction - one ovoviviparous development and one as a free-swimming larva. We are now analysing the reproductive modes along the entire distribution range of the species.

A transition between the two extremes can be identified, which contradicts poecilogony. Various factors could be responsible for the development and maintenance of reproduction patterns, such as the salinity of the sea surface. We see this as a possible main influencing factor.

Snail shells become family tree data

For the study of the reproductive modes of P. sulcatus, we will prepare a case study of the evolutionary systematics of planaxids with a revision of the seven genera and at least eleven species of this taxon.

Methodologically, we will mainly perform a geometric morphometry of the shells and analyse the radulae (rasp tongue) of the animals. In addition, a molecular phylogeny of the Planaxidae will be established.

The resulting revision will allow us to reconstruct the distribution ranges of the planaxid species and serve as a basis for analysing their biogeography and biodiversity patterns.

Distribution areas provide information about biodiversity patterns

As a result, the planaxids can confirm the current findings of research in these areas. Thus, our project emphasises contemporary distribution and diversity patterns of marine ectothermic organism groups living in coastal areas.