What is the "Sea Cow" Mentioned in Numbers 4:6?

What is a “sea cow” (Numbers 4:6)?

Sea cows are dugongs, marine animals abounding on the coral banks of the Red Sea and in other tropical waters. A dugong grows to 11 feet long, with a round head, fish-like tail and flippers for forelimbs. Their appearance is similar to seals. Because the Red Sea borders ancient Egypt, it’s not surprising that Israel used their hides for various purposes.

–The Quest Study Bible