Rhabdosome

Rhabdosome is a term used in paleontology and protozoology to describe a rod-like skeletal framework found in certain shelled protists, particularly some radiolarians and related fossil groups. The word derives from Greek rhabdos meaning rod and soma meaning body. In these organisms, the rhabdosome refers to an internal skeleton composed of slender, rod-shaped elements that connect to form an axial spine or lattice that supports the outer test or cell body. The arrangement can be linear, branching, or mesh-like, and may be integrated with, or distinct from, the external silica-based test that is commonly preserved in fossils.

Function and significance: The rhabdosome provides mechanical support, contributes to buoyancy, and influences the overall form and rigidity of the organism. In the fossil record, rhabdosomes aid in species identification and help illuminate the morphological evolution of early protists. The study of rhabdosomes, typically through light and electron microscopy of preserved microfossils, informs on patterns of biomineralization and can contribute to reconstructions of ancient environments.

Occurrence: The term is most often used in descriptions of radiolarian skeletons and some related protists from Paleozoic to Mesozoic strata; usage varies among authors, and older literature may employ the term with somewhat different definitions.

See also: Radiolaria, Foraminifera, Skeletal microstructures, Radiolarian skeleton.