Research on radular growth in Oxychilus (Drouetia) atlanticus was presented at the 5th Congress of the European Malacological Societies, September 2-6, at the University of the Azores.
At the same time, our work on the evolution of Drouetia and the geological history of São Miguel was presented at the 2nd Atlantic Islands Neogene: International Congress, concomitantly held at the University of the Azores.

Additional information at http://www.euromalac2008.org/.

Radular growth in Oxychilus (Drouetia) atlanticus (Morelet & Drouët, 1857)

Ana Bárbara Paquete Velosa¹ and António M. de Frias Martins^2
1Departamento de Biologia and ²CIBIO – Pólo Açores, Universidade dos Açores, 9501-801 Ponta Delgada, São Miguel, Açores, Portugal jimileca@gmail.com

The molluscan radula, due to its complexity, has been traditionally used as a taxonomic character at the specific and supraspecific levels. However, its morphology has been recorded to change throughout the development of the individual, thus demanding further caution when comparisons are made.

A possible radiation of the endemic zonitid subgenus Drouetia Gude, 1911, in the island of S. Miguel, is being investigated.  Besides the two recorded species, Oxychilus (Drouetia) atlanticus (Morelet & Drouët, 1857) and O. (D.) batalhana De Winter, 1989, evidence is growing to support a more complex taxonomic situation. The pertinence of the use of the variation of radular characters as taxonomically diagnostic in the analyses of samples with various sizes at maturity was assessed. A study was conducted in a sample of O. (D.) atlanticus from Abelheira, with shell diameters ranging from 2.0 to 6.4 mm and the size of the shell was correlated with the morphology of the radula.

The shape of the radular teeth remained the same throughout that period of development, but the number of marginal teeth per row was found to increase with size.  On the other hand, the number of rows remained fairly constant throughout the size range, thus revealing a parameter of taxonomic importance to be taken into account on the main study.

This work was part of a requirement for the undergraduate course of Biology, branch of Environmental Biology and Evolution.

A gut feeling: what comparative anatomy of the endemic Oxychilus (Drouetia) tells about the age of São Miguel island, Azores

António M. de Frias Martins
CIBIO – Pólo Açores, Departamento de Biologia, Universidade dos Açores, 9501-801 Ponta Delgada, São Miguel, Açores, Portugal frias@uac.pt

The most obvious approach to assess the age of an island is through the application of geological methods that compare isotope proportions.  However, since almost its very beginning, an island is populated by a succession of species that evolve there and may depict, in their evolutive history, the age and also the main events that shaped the geological history of that island.

The geomorphology of São Miguel island has been thoroughly studied, and the present island is currently accepted to have resulted from the merging of two islands. Its oldest sector, Nordeste, was first thought to have appeared 4 My ago, but recent age determinations have shown the age of these oldest exposed parts of the island to be less than one million years old.

Comparative anatomy of recent species does not yield geological age; however, the extent of intra-island morphological divergence in a particular species complex (clade), when compared with similar units in other islands of known ages, should provide grounds for comparison and assessment.

The endemic land mollusc subgenus Drouetia is spread throughout the archipelago and clusters of species have been identified in various islands, their morphological divergence variously expressed according to the accepted age of the island they live in.  In São Miguel, only one species has been recorded, Oxychilus (Drouetia) atlanticus (Morelet & Drouët, 1857), of which O. (D.) batalhana de Winter, 1989 has been considered a junior synonym.  Extensive investigation throughout the island has revealed a swarm of species, consistent with the geomorphological succession of the island’s formation that indicates very recent merging of two former islands.  Moreover, the morphological affinity of the populations/species throughout the island, when compared to that observed in older islands, appears to support the younger age assessment for São Miguel.