Marine life asexually by binary fission, fragmentation, or budding; unlike bacteria and eukaryotes, no known species forms spores. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet. Archaea are a major part of Earth's life and may play roles in both the carbon cycle and the nitrogen cycle. Of eukaryotic groups, the protists are most commonly unicellular and microscopic. This is a highly diverse group of organisms that are not easy to classify. Several algae species are multicellular protists, and there are marine slime molds have
Freshwater snail the highlighted families consist entirely of freshwater species, but some of them also contain, or even mainly consist of, marine species.) The following cladogram is an overview of the main clades of gastropods based on the taxonomy of Bouchet & Rocroi (2005), modified after Jörger et al. (2010) and simplified with families that contain freshwater species marked in boldface: (Marine gastropods (Siphonarioidea, Sacoglossa, Amphiboloidea, Pyramidelloidea) are not depicted within Panpulmonata for simplification. Some of these highlighted families consist entirely of freshwater species, but some of them also contain, or even mainly consist of, marine species.) The Neritimorpha are a group