West Indian Manatee - Trichechus manatus, is divided into two subspecies based on skull anatomical differences, Trichechus manatus latirostrus (Florida manatee) andTrichechus manatus manatus (Antillean manatee). Each possessing 48 chromosomes.
- Florida manatee - Trichechus manatus latirostrus, reaches a possible length of 3.9 meters and weight of 1,500 kilograms. They are generally gray to dark-brown in color, with rough, bumpy skin.
- Antillean manatee - Trichechus manatus manatus, is very close to the Florida manatee in appearance, with a maximum length of 3.5 meters and weight of 1,000 kilograms. Externally, the subspecies are indistinguishable.
Amazonian Manatee - Trichechus inunguis, the smallest of the living manatees in length with the longest recorded measurement only 2.8 meters, lives in the Amazon basin in South America. It typically bears small white or pink patches on its smooth skin. Less obvious differences include: a lack of nails on the pectoral flippers, longer flippers, smaller teeth, and a longer, narrower rostrum (anterior skull) relative to other manatee species. This species is also the only one confined to fresh water. Its total number of chromosomes is 56.
West African Manatee - Trichechus senegalensis, is roughly the same size as a West Indian manatee, but has more protruding eyes, a blunter snout, a less robust body, and a more downward-pointing rostrum. The chromosomal compliment is unknown.
Dugong - Dugong dugon, with a maximum length of 3.3 meters and weight of 400 kilograms, is remarkably different from the manatee in many ways. Dugongs have smooth skin, a split tail fluke, and tusks which erupt in post-pubescent males only. They are the most marine genus of Sirenians in habitat preference, and are the only indo-pacific sirenians alive today, due to the human-caused extinction of the Stellar’s sea cow during the late 1700’s.