1. of or relating to a type of fish scale that is small, smooth, and tooth-like, found on sharks and rays
Usage: technical; zoology

Examples

• Sharks have placoid scales that reduce drag as they swim through water.
• The placoid scales of rays are similar in structure to those of sharks.
• Unlike cycloid scales found on most fish, placoid scales are harder and more pointed.
• Marine biologists study placoid scale patterns to understand shark evolution.