Vesieliöisillä

Vesieliöisillä is a Finnish grammatical form that functions as the adessive plural. It is typically interpreted as the form indicating location or association with aquatic organisms. The base noun vesieliö means an aquatic organism (water + animal), and the standard adessive plural form is vesieliöillä, used to say “on/at the aquatic organisms” or “with the aquatic organisms.” Vesieliöisillä is not a common standard form in many dictionaries and is often regarded as nonstandard, a misspelling, or a product of applying a different adjective-like inflection pattern to vesieliö or to an adjective such as vesieliöinen in some contexts.

Formation and use

In everyday biology and ecology Finnish tends to use vesieliöillä for the adessive plural of vesieliö. The form vesieliöisillä may appear in texts as a variant, possibly arising from attempts to create an adjective-like inflection (for example from vesieliöinen) or through dialectal or idiosyncratic usage. When referring to location or action related to aquatic organisms, vesieliöillä remains the standard choice.

Ecological scope

Vesieliöissä and vesieliöt cover broad categories of organisms living in water, including microorganisms, algae, invertebrates, and vertebrates. The term is used in discussions of freshwater and marine ecosystems, biodiversity, and ecological interactions, such as host–parasite relationships or symbiotic associations that occur on the surfaces or within communities of aquatic organisms.

See also

vesieliö

vesieliökunta (aquatic fauna)

vesiekosysteemi (aquatic ecosystem)

Note: For most formal purposes, vesieliöillä is the recognized adessive plural; vesieliöisillä is less common and may signal nonstandard usage.