Kinetids, intracellular systems that are diverse but conserved in various protoctist
taxa, provide clues to identification of cells and whole organisms.
Tardigrades, rotifers, acarid mites, and insects (mainly springtails and flies) complete the range of groups found, together with some heterotrophic protoctists
traditionally considered as protozoans.
The Eucarya (meaning "true nucleus") include protoctists
, animals, plants, and fungi.
This build-up of CO2 may have been the cause of the apparent release of calcium carbonate during the Cretaceous period in shallow sea areas where many corals and mollusks lived, all in a symbiotic relationship with photosynthetic protoctists
Dead plants are colonized by several types of organism, including bacteria, fungi, protoctists
, and small animals such as nematodes.
The silicoflagellates are medium-sized flagellated protoctists
(20-70 microns), with a thin membrane, numerous chromatophores and a highly distinctive internal reticulate skeleton, generally showing four-fold or six-fold symmetry.
Various heterotrophic protoctists
also produce external skeletons that persist after the death of the more active part.
Filter feeders like sponges, tunicates, and some bivalve mollusks always have a large number of internal commensal organisms, including such diverse groups as protoctists
, amphipods, copepods, lamellibranchs, crabs, worms, and even fish.
They contain a very special flora and fauna, consisting mainly of cyanobacteria, diatoms, benthic protoctists
, and some harpacticoid crustaceans, as well as insect larvae.
Ongoing research to find natural toxins from marine organisms that serve to prevent biological succession that leads to fouling (such as glycoproteins from bacteria, diatoms, protoctists
, algae, and invertebrates), began a decade ago.
The soil is occupied by protoctists
, nematodes, oligochaeta (earthworms), acarina (mites and ticks), collembola (springtails), and diptera larvae.
Growing with the trees, around them and on them, underneath them and within them, are the thousands of species of animals, plants, fungi, protoctists
and bacteria making up the world's most diverse biota.
These alkaloids are lethal to many protoctists
, the reason for their effectiveness against malaria and dysentery.
There are in fact only protoctists
, rotifers, and crustaceans (mainly copepods, such as the genus Cyclops, and cladocerans, such as Daphnia) and some insect larvae (Chaoborus).
The components of the microbial community in the Ciso pool may also include phototrophic protoctists
(unicellular algae and some ciliates and flagellates) that also eat bacteria, bacterial primary producers, bacteria that attack and devour other bacteria, and organisms of different groups that live together, forming symbiotic, commensal, mutualist, or parasitic associations.