Number of species in the collection: 20.

Back to Domain: Eukaryota

Pictures of Chromalveolata:                             

Characteristics of Heterokontophyta:           

The Chromalveolata is a kingdom of organisms that encompass species with highly varied morphologies and lifestyles. Its name derives from two major lineages of living organisms, the Chromista and the Alveolata. It is a globally distributed group, found from deserts to poles, or from mountain peaks to the abyssal depths of the oceans. Although some species can dehydrate without dying, they are water-dependent organisms, as they need to be moist to be active.

It is a very difficult group to define due to its great variability, ranging from tiny unicellular organisms to multicellular individuals exceeding 100 meters in length. This group includes, for example, brown algae common in the seas, diatoms frequent in moist soils and water masses, dinoflagellates, microscopic organisms capable of forming toxic blooms or living symbiotically with corals, apicomplexans, which parasitize animals, oomycetes, which parasitize plants, or ciliates, very common and morphologically complex unicellular organisms.

The Chromalveolata derive from a unicellular ancestor, which probably fed on unicellular algae. One of these algae, belonging to the group of Rhodophyta or red algae, after being ingested by the cell managed to survive inside it. It is unknown whether this phenomenon occurred suddenly or gradually, but it led to the host cell acquiring photosynthetic capacity by maintaining the alga inside it. This relationship, through evolution, was perfected so that an organism with photosynthetic capacity emerged without the need to maintain the alga inside, retaining the chloroplasts of the red algae and losing most of its cellular content as well as its DNA, while some important genes migrated to the host nucleus. Thus, the Chromalveolata descend from the fusion of a primitive unicellular organism with a red alga (which originated from the fusion of a non-photosynthetic unicellular organism with a photosynthetic bacterium of the group of Cyanobacteria). This organism diversified into major lineages, some of which eventually lost photosynthetic capacity. In this way, there are some non-photosynthetic Chromalveolata, but many of them still retain structures derived from the red alga, although these have other functions not related with the photosynthesis, such as synthesizing lipids or amino acids. Many of these groups have transitioned to a parasitic life. Additionally, some lineages, after losing the photosynthetic capacity, have regained it through endosymbiosis with new algae from different branches of the tree of life.

The following cladogram shows the evolutionary relationships of the main lineages of the kingdom: