Biology STAAR (State of Texas Assessments of Academic Readiness) Practice Test

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What feature distinguishes mollusks from other invertebrates?

Presence of jointed appendages
Possession of a shell in most species
Having a segmented body
Exhibiting radial symmetry

The correct answer is: Possession of a shell in most species

The distinguishing feature of mollusks from other invertebrates is the possession of a shell in most species. This characteristic is significant because it plays a critical role in the protection and survival of these organisms. Mollusks typically have a hard external shell made of calcium carbonate, which serves as a protective barrier against predators and environmental hazards. While not all mollusks possess a shell (for instance, octopuses and some limpets), the presence of a shell is a common trait among the majority, including snails, clams, and squids, thereby setting them apart from many other invertebrate groups. This shell is also a key factor in the classification and study of mollusks within the broader context of biological diversity.