It’s eel-shaped and leopard-spotted, and it has no hind-limbs. It grows to two feet long. And yet until recently, hardly anyone had ever seen it.

A team of researchers has discovered of new species of salamander in the pine forests of northern Florida and southern Alabama. The so-called reticulated siren is the largest vertebrate found in the United States in decades, and the first new member of its family since 1944.

“It’s a really cool animal,” said David Steen, a conservation biologist at the Georgia Sea Turtle Center and an author of a genetic analysis of the salamander published in PLOS One. The salamander’s distinctive patterning “jumps out immediately,” he said.

Known for their size and bushy gills, sirens are a fixture in Southeastern swamps and watery ditches. Previously, Dr. Steen said, the genus was assumed to contain only two species: the lesser siren and greater siren, which can grow to three feet in length, one of the longest American salamanders.