What is the most critical physical feature that places ticks in the Class Arachnida rather than the Class Insecta?
Answer
Adult ticks possess eight legs, whereas insects have six
Ticks are classified as arachnids because adult ticks possess eight legs. Insects, by definition, possess only six legs. Other distinguishing arachnid features mentioned include the lack of antennae and the body structure.

Related Questions
What is the most critical physical feature that places ticks in the Class Arachnida rather than the Class Insecta?Which classification level specifically defines organisms as ticks, distinguishing them from other Acari like dust mites?What morphological feature is characteristic of Ixodidae, or Hard Ticks?During which life cycle stage do ticks technically possess only six legs?In terms of body structure typical of arachnids, how is the tick's body usually described structurally?What term describes ticks' absolute requirement to feed on a host's blood to complete their life cycle?What behavior, involving climbing onto vegetation and waiting for a host, is noted as more characteristic of Hard Ticks?What are the specialized mouthparts used for anchoring onto a host and feeding on blood called?Which two primary families does the Order Ixodida divide into, based on morphological differences?What is the primary component that defines belonging to the Phylum Arthropoda?