Natural Science CLEP Prep Practice Exam 2025 - Free Practice Questions and Study Guide

A barnacle is classified as a mollusk due to its characteristics and anatomical features. Mollusks are invertebrate animals that have a soft, unsegmented body, a muscular foot, and usually a shell. Unlike insects, barnacles do not have jointed legs or wings. They also do not have the typical features of fish, such as scales, gills, or a backbone. As for reptiles, barnacles do not possess any of their defining traits, such as a shelled egg, dry skin, or cold-blooded metabolism. Therefore, the best answer for the type of organism a barnacle is, is a mollusk.