Question

Are Rhizaria protists?

Answer 1

Hint: Rhizaria is a species-rich supergroup of mostly unicellular eukaryotes. Except for the chlorarachniophyte and three species of the genus Paulinella in the phylum Cercozoa, they are all non-photosynthetic, but many foraminifera and radiolaria have a symbiotic relationship with unicellular algae.

Complete answer:
The Rhizaria supergroup includes many amoebas with thin thread-like, needle-like or root-like pseudopodia (Ammonia tepida, a species of Rhizaria) rather than the wider lobed pseudopodia of the Amoebozoa.

Many rhizards carry out elaborate and beautiful tests—the armor-like coverings for the body of the cell—composed of calcium carbonate, silicon or strontium salts. Rhizarians play important roles in both carbon and nitrogen cycles. When rhizarians die and their tests sink into deep water, carbonates are out of reach of the majority of the decomposers, locking carbon dioxide away from the atmosphere.

A multicellular shape, Guttulinopsis vulgaris, a cellular slime mold, has also been described. This supergroup was proposed in 2002 by Cavalier-Smith. Described mainly from rDNA sequences, they vary considerably in form, having no distinct morphological characters (synapomorphy) but are mostly amoeboids with filose, reticulosis, or microtubule-supported pseudopods.

Many produce shells or skeletons, which may be quite complex in structure, and they make up the vast majority of protozoan fossils. Almost all of them have mitochondria with tubular crystals.

Note: Rhizaria is part of the Diaphoretic clade along with Archaeplastida, Alveolata, Cryptista, Haptista and Halvaria.Historically, many rhizards were considered animals due to their motility and heterotrophy. However, when a simple animal-plant dichotomy was superseded by recognition of additional kingdoms, taxonomists generally placed Rhizarians in the Protista kingdom.