Onteloiden

Onteloiden is the Finnish noun used to refer to internal body cavities in animals and other multicellular organisms. The root ontelo means cavity or hollow space; onteloiden is the plural form used when speaking of multiple cavities or the cavity system as a topic (for example, onteloiden kehitys, the development of cavities). In English-language biology, the closest general terms are body cavity and, for true cavities in certain groups, coelom.

In animal biology, body cavities are a key structural and developmental feature used to describe organismal plans. Organisms may be acoelomates (lacking a body cavity), pseudocoelomates (having a pseudocoel), or coelomates (with a true body cavity). The formation of onteloiden during embryogenesis can occur by schizocoely or enterocoely, depending on the lineage. The study of these cavities informs taxonomy, physiology, and the evolution of organ systems, including digestion, circulation, and hydrostatic support.

Usage notes: Onteloiden appears mainly in Finnish-language texts on anatomy and developmental biology. In English, authors typically refer to coelom or body cavities rather than using the Finnish term.