The anal fin has a single spine and 9 soft rays.

The motorcycle engine is held in a single cradle with a single spine.

The motorcycle engine is suspended from a single spine.

The single closest spine is only about two-thirds the height of the others.

They each have a single stiff spine at the tip, hence the specific name monacantha.

On each side of abdominal segments six through nine, there is a single, rear-facing spine.

There is a single saw-toothed spine located on the latter half of the tail.

There is also a single, rear-facing spine on each side of abdominal segments eight and nine.

They may also have single spines on body surface.

The single central spine is rare or absent and it is formed only in older plants.