Siphonophores, particularly species like the giant siphonophore (Praya dubia), can grow up to 40-50 meters in length, making them the longest animals in the world. While lion's mane jellyfish are often cited as the longest, siphonophores are colonial organisms that can extend even longer. A siphonophore discovered in 2020 was measured at approximately 46 meters, confirming their status as the longest animals.