Molluscs are the invertebrates with the highest level of morphological adaptation, allowing their establishment in the majority of aquatic environments. In fact, the highest fitness level is achieved by those species, such as bivalves, adapted to live on cryptic ecosystems build by themselves. In order to describe the diversity of cryptic bivalve molluscs in two sampling areas in the western coast of the Gulf of Venezuela (Kazuzain and Porshoure), samples were manually collected in June and July 2010, respectively, by snorkelling in random coralline rocks (3-5m depth), and stored them in 10% formalin for transportation. In the laboratory, the rocks were fragmented and all organisms within removed. Diversity was determined by the Shannon-Wiener index for each locality, and the Kruskal-Wallis test was used to compare the bivalves composition between both localities in order to establish a possible significant difference (p<0.05). Five families, eight genera and ten species were found (n=53). Lithophaga corrugata, Lioberus castaneus, Gregariella coralliophaga and Choristodon robustus are reported as new records for Venezuela; while Leiosolenus appendiculatus, Lithophaga teres and Malleus candeanus are new records for the Maracaibo Lake System. No significant difference was found between the studied communities (p=0.1587). The specimens remain in the invertebrates collection of the Biology Museum, La Universidad del Zulia (MBLUZ), Maracaibo, Venezuela. PUBLICATION ABSTRACT