Which of the following best describes invertebrates?

The best description of invertebrates is that they are animals that lack backbones. This definition encompasses a vast group of organisms, including insects, arachnids, mollusks, crustaceans, and more. Invertebrates represent the majority of animal species on Earth and exhibit a wide range of anatomical and behavioral diversity.

Some characteristics that define invertebrates include their body structures, which can be quite varied and do not include the vertebral column or spine found in vertebrates (animals with backbones). This distinction is fundamental in biological classification, as it separates a large number of animal phyla that contribute significantly to ecological systems and biodiversity.

The other options present characteristics that do not fit the definition of invertebrates. For instance, the reference to a backbone directly contradicts the definition of invertebrates. Regarding survival in extreme conditions, while some invertebrates can thrive in harsh environments, not all invertebrates share this capability, making it an inaccurate classification. Lastly, the claim that invertebrates are exclusively aquatic is also incorrect, as many invertebrates, such as insects and certain types of snails, can be found thriving in terrestrial environments. Thus, the definition emphasizing their lack of a backbone is the most accurate and