Which term best describes an organism that does not possess a standardized form of symmetry?

The term that best describes an organism that does not possess a standardized form of symmetry is 'asymmetrical.' This means that the organism cannot be divided into mirror-image halves, indicating a lack of any symmetrical arrangement. Many organisms, especially certain invertebrate species like sponges and some types of corals, exhibit this characteristic, which is often a result of their unique evolutionary adaptations.

Although 'irregular' can also refer to a lack of symmetry, it is more commonly used to describe non-uniform shapes rather than a definitive absence of symmetry. 'Anisotropic' refers to properties that change based on direction, and 'multisymmetrical' implies multiple forms of symmetry, which is not applicable to organisms that are entirely asymmetrical. Thus, asymmetrical is the most precise term for an organism lacking a standardized form of symmetry.