Everything about The Rhizaria totally explained
The
Rhizaria are a species-rich supergroup of
protists. They vary considerably in form, but for the most part they're
amoeboids with filose, reticulose, or microtubule-supported pseudopods. Many produce shells or skeletons, which may be quite complex in structure, and these make up the vast majority of protozoan fossils. Nearly all have
mitochondria with tubular cristae. There are three main groups of Rhizaria:
Cercozoa - Various amoebae and flagellates, usually with filose pseudopods and common in soil
Foraminifera - Amoeboids with reticulose pseudopods, common as marine
benthos
Radiolaria - Amoeboids with axopods, common as marine
plankton
A few other groups may be included in the Cercozoa, but on some trees appear closer to the Foraminifera. These are the
Phytomyxea and
Ascetosporea, parasites of plants and animals respectively, and the peculiar amoeba
Gromia. The different groups of Rhizaria are considered close relatives based mainly on genetic similarities, and have been regarded as an extension of the Cercozoa. The name Rhizaria for the expanded group was introduced by
Cavalier-Smith in 2002, who also included the
centrohelids and
Apusozoa.
Evolutionary relationship
Rhizaria is part of the
bikont clade, which also comprises the
Archaeplastida, the
Chromalveolata, the
Excavata, and some smaller, unresolved groups such as the
Apusozoa and the
Centrohelida. As bikonts, they all descend from a
heterotrophic eukaryote with two
flagella.
Historically, many rhizarians were considered
animals, with their motility and heterotrophy as justification. However, when the five-kingdom system took prevalence over the animal-plant dichotomy, the rhizarians were put into the kingdom
Protista. Then, after
Woese published his three-domain system, because of the paraphyly of the kingdom
Monera, taxonomists turned their attention to the eukaryote domain, and the inherent paraphyly of
Protista. After much debate, which continues to this day, Rhizaria emerged as a monophyletic group.
Further Information
Get more info on 'Rhizaria'.
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