However, copper alone is not impervious to diatom and algae fouling. The mitochondria and the plastids of the diatom somehow remain functional. The drier climate is also reflected by increased salinity indicated by diatom analysis. One key factor that must be noted with freshwater diatom deposits is species identification. The species of diatom may also differ among deposits. Several systems for classifying the individual diatom species exist. It is assumed that Madagascar harbours a rich endemic diatom flora. One known symbiosis between the diatom "Hemialus" spp. Like the diatom endosymbiont's diatom ancestor, the chloroplasts have triplet thylakoids and pyrenoids. The species of diatom is dependent upon the age and paleoenvironment of the deposit. Nitzschia is a common pennate marine diatom. Diatomaceous earth (diatomite) is a collection of diatom shells found in the earth's crust. Scientists are researching on diatom light absorption, using the marine diatom of Thalassiosira. Some dinophytes, like "Kryptoperidinium" and "Durinskia" have a diatom (heterokontophyte) derived chloroplast.