How do triple spines of the family Triacanthidae differ from spikefishes?

The family Triacanthidae, known as triple spines, are shallow-water derivatives of the spikefishes (family Triacanthodidae). While spikefishes are deepwater species characterized by a nonstreamlined body, a truncated or rounded tail, and a deep caudal peduncle, the Triacanthidae exhibit several distinct evolutionary adaptations for more rapid swimming:1

• Body Shape: Triacanthidae have a relatively streamlined body compared to the nonstreamlined form of spikefishes.1
• Caudal Fin and Peduncle: Triple spines possess a deeply forked caudal fin and a slender caudal peduncle, whereas spikefishes have a truncated or rounded tail and a deep caudal peduncle.1
• Fin Proportions: In Triacanthidae, the base of the soft dorsal fin is much longer than the base of the anal fin, while in spikefishes, the soft dorsal and anal fins are of approximately the same length along their bases.1

These differences reflect the transition of Triacanthidae from the deepwater habitats occupied by their primitive spikefish ancestors to shallower environments.1