First Taxonomic Records of Epizoic Freshwater Algae on Golden Apple Snails (Pomacea canaliculata Lamarck) from Rice Paddies in Laguna (Philippines)

Abstract

In rice paddies where hard substrate is considered as a limiting resource, the hard shell of mollusks can serve as a primary settling space of algal epibionts. The study presents the first taxonomic survey to report and describe epizoic algae in freshwater snail – golden apple snail (GAS) (Pomacea canaliculata Lamarck) – found in agricultural areas. A total of 17 microalgal taxa belonging to 12 orders, 16 families, and 17 genera were taxonomically identified and described from the collected samples, all of which are considered new distributional records of microalgae in the Philippines. The study shows Cyanobacteria (six species) as the main group of epizoic microalgae present in shell surfaces of the mollusk, followed by Bacillariophyceae (four species), Chlorophyceae (three species), Zygnematophyceae (two species), Trebouxiophyceae (one species), and Euglenophyceae (one species). Also, the survey reported the occurrence of a photosynthetic euglenoid, Phacus hamatus Pochmann, described for the first time in the Philippines. Diagnostic descriptions and taxonomic keys are presented to differentiate the epizoic algal taxa associated with GAS. The survey shows important taxonomic records on the composition and species diversity of epizoic algae from freshwater snails found in terrestrial habitats of the Philippines.