In the threespine stickleback, how many dorsal spines are present and where are the pelvic spines located?

In the threespine stickleback, how many dorsal spines are present and where are the pelvic spines located?

• A. Three dorsal spines; pelvic spines on the dorsal side
• B. Five dorsal spines; no pelvic spines
• C. Three dorsal spines; two pelvic spines projecting from the pelvis on the ventral side
• D. Two dorsal spines; pelvic spines on the ventral side

Answer: (C)

In the threespine stickleback, you’ll find three dorsal spines along the back, and two pelvic spines that project forward from the pelvis on the ventral (belly) side. This specific arrangement—three dorsal spines plus two forward-projecting pelvic spines—is the defining feature used to identify this species. The dorsal spines are the rigid spines that reinforce the dorsal fin region, while the pelvic spines extend from the pelvic girdle toward the front of the body. Other options misstate either the number of dorsal spines or the location/presence of pelvic spines, which doesn’t match the anatomy of the threespine stickleback.

In the threespine stickleback, you’ll find three dorsal spines along the back, and two pelvic spines that project forward from the pelvis on the ventral (belly) side. This specific arrangement—three dorsal spines plus two forward-projecting pelvic spines—is the defining feature used to identify this species. The dorsal spines are the rigid spines that reinforce the dorsal fin region, while the pelvic spines extend from the pelvic girdle toward the front of the body. Other options misstate either the number of dorsal spines or the location/presence of pelvic spines, which doesn’t match the anatomy of the threespine stickleback.