High species richness of epiphytic Mastogloia (Mastogloiales: Bacillariophyceae) on Thalassia testudinum along the coast of Campeche, southern Gulf of Mexico

Diatoms of the genus Mastogloia are naviculoid forms that are generally easy to discriminate due to the presence of marginal chambers known as partecta. They exhibit a wide marine distribution, and are basically benthic forms usually conspicuous in epiphytic and epipelic diatom assemblages. Our objective was to identify species of Mastogloia epiphytic on Thalassia testudinum blades from the southern Gulf of Mexico region. Blades of T. testudinum were collected off the coast of Campeche State, Mexico; the epiphytic diatoms were scrapped off, cleaned and mounted on permanent slides for identification under light microscopy. A total of 76 Mastogloia taxa were recorded. This is the highest number of Mastogloia taxa recorded for Mexican coasts. Seven taxa had not been observed for the region: Mastogloia angusta, M. belaensis, M. depressa, M. ovalis, M. pseudolacrimata, M. regula, and M. urveae. Likewise, 20 Mastogloia species are new records for the Gulf of Mexico, while 15 are new records for Mexican coasts overall. This study confirms that Mastogloia species are mostly distributed in tropical and subtropical habitats, and shows that much floristics and formal taxonomy are required on benthic diatoms from different types of substrata for Mexican littorals.