Synthesis of the knowledge of visual systems diversity in Mollusca, with emphasis on Bivalvia

Abstract

The diversity of metazoan visual systems is astonishing, and numerous recent studies have been advancing our knowledge by incorporating novel techniques and approaches. The phylum Mollusca exhibits huge diversity of ocular structures, and Bivalvia is the most diverse class in this aspect, bivalves being regarded as potential models for the study of visual systems evolution. Firstly, this paper explores the classification of visual diversity in Metazoa, and the main current hypotheses on homologies and convergences in animal photoreception. Then, a critical review of the knowledge of molluscan visual systems is presented, with emphasis on ocular organization in bivalves. Finally, gaps in our knowledge and perspectives for future research are discussed, as well as current paradigms in animal vision evolution.