Cocconeis neothumensis is an epiphytic diatom in the family Cocconeidaceae, closely related to the type species Cocconeis thumensis but representing a morphologically and molecularly distinct taxon distinguished by the specific architecture of its silica frustule valves. The genus Cocconeis comprises adnate diatoms that attach firmly to solid substrates in aquatic environments, including the surfaces of submerged macrophytes, periphyton mats, and sediment particles in rivers, lakes, and coastal habitats. Cocconeis neothumensis has been recorded from freshwater bodies in South America and other regions, contributing to the benthic periphyton communities that coat submerged surfaces in well-lit aquatic habitats. The frustule ornamentation—including the density and arrangement of transapical striae and the morphology of the raphe system—provides the key morphological characters used to distinguish this species from its congeners under light and electron microscopy. Like all diatoms, C. neothumensis requires dissolved silicic acid to construct its frustule and depends on phosphorus and nitrogen availability for growth, making it a sensitive indicator of nutrient conditions in monitored water bodies. Periphytic diatom communities including Cocconeis species are widely used in ecological assessment frameworks such as the European Water Framework Directive to evaluate the biological quality of freshwater bodies based on assemblage composition. Conservation status is not formally evaluated.