What crucial difference separates Family Istiophoridae from Family Xiphiidae (Swordfish)?
Answer
Presence of two pelvic fins
The distinction between the family Istiophoridae (true billfishes, including Marlins and Sailfish) and the related family Xiphiidae (Swordfish) is rooted in specific morphological characteristics, most notably regarding the pelvic fins. Members of Istiophoridae, such as the White Marlin, are characterized by possessing two distinct pelvic fins. Conversely, the Swordfish, belonging to Xiphiidae, possesses only a single pelvic fin. Other shared features of Istiophoridae include a deeply forked caudal fin and a prominent dorsal fin that often folds neatly into a groove when the fish is swimming at high velocity.
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