How many dorsal spines and pelvic spines does the threespine stickleback possess?

• A. Three dorsal spines and two pelvic spines
• B. Four dorsal spines and three pelvic spines
• C. Five dorsal spines and two pelvic spines
• D. Two dorsal spines and one pelvic spine

Answer: (B)

Counting dorsal and pelvic spines is a straightforward way to describe a stickleback’s armor and use as a identifying feature. The threespine stickleback is described in many sources as having four dorsal spines along the back and three spines in the pelvic region near the belly. The dorsal spines are the spines in front of the dorsal fin, while the pelvic spines are part of the pelvic girdle toward the underside. This particular count—four on the dorsal side and three on the pelvic side—provides a clear, repeatable pattern that the study materials use to identify the species, so it aligns with the expected description in this context. Other counts would not match the standard description used here.