What is a common characteristic of invertebrates?

Invertebrates are characterized by the absence of a backbone or vertebral column. This classification includes a diverse group of animals such as jellyfish, worms, mollusks, and arthropods, among others. The lack of a backbone allows for greater mobility in various environments, including both aquatic and terrestrial ecosystems. Unlike vertebrates, invertebrates utilize alternative support structures, like exoskeletons (in the case of arthropods) or hydrostatic skeletons (in animals like jellyfish), which aid their movement and form.

The other characteristics mentioned do not universally apply to invertebrates. Having skeletons made of bone is a defining feature of vertebrates. While many invertebrates are found in aquatic environments, they are not exclusively aquatic, as there are numerous terrestrial species as well. Additionally, while some invertebrates, such as certain mollusks, possess gills for respiration, not all invertebrates have gills; for instance, many use different methods for gas exchange. Thus, the most accurate and defining characteristic of invertebrates is their lack of backbones.