Sources : Ceruleum

Pliny the Elder [1st century CE] (Natural History, Book 9, 17): Statius Sebosus gives an extremely marvelous account of worms in the same river [Ganges] that have a pair of gills, measuring 90 feet; they are deep blue in color, and named from their appearance [ceruleum is a green-blue color]; he says that they are so strong that they carry off elephants coming to drink by gripping the trunk in their teeth. - [Rackham translation]

Gaius Julius Solinus [3rd century CE] (De mirabilibus mundi / Polyhistor, Chapter 52.41): Statius Sebosus says, among especial marvels, that this same river [Ganges] abounds in worms, blue in both name and color. They have two arms, not less than six cubits in length, of such great strength that they drag elephants who come to drink into the depths, seizing their trunks by biting. - [Arwen Apps translation, 2011]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Marine monsters 6.14): Ceruleus, as Solinus says, is a sea monster in name and color, which the river Ganges brings up. This beast has two arms, the length of a cubit; it is no less than six cubits long. This monster is so robustly strong, that it drags huge beasts that come to the shore with its arms into the depths, seizing them with its bite. - [Badke translation/paraphrase]