Interesting, I watched a show on a seal manatee hybrid people in Florida claim to have seen.
I hope you didn't watch the whole thing. Seals are rather distant from manatees; seals are related to terrestrial bears and mustelids, and manatees' closest terrestrial relatives are elephants.
This would be like seeing a bobcat/raccoon hybrid.
From the taxonomic trivia desk:
The mnemonic
King Philip Came Over For Good Spaghetti describes seven taxonomic grades, but pedants have over 100 intermediate grades! For example, in between Class and Order no less than 23 intermediate grades are in use: Class, Subclass, Infraclass, Parvclass, Division, Subdivision, Section, Subsection, Group, Subgroup, Superlegion, Legion, Sublegion, Infralegion, Supercohort, Cohort, Subcohort, Magnorder, Superorder, Series, Subseries, Grandorder, Mirorder, Order.
The Silvery Langur (or Lutung) and Proboscis Monkey (Long-Nosed Monkey) are in the same Subfamily — Colobinae (Leaf-eating Monkeys) — but that Subfamily has about ten extant genera divided into three genus groups, and the two species are in different genus groups.
Hybrids of different genera in the same subfamily are rare and usually infertile. Sheep-Goat is a classic example:
Wikipedia said:
At the Botswana Ministry of Agriculture in 2000, a male sheep impregnated a female goat resulting in a live male offspring. This hybrid had 57 chromosomes, intermediate between sheep (54) and goats (60) and was intermediate between the two parent species in type. It had a coarse outer coat, a woolly inner coat, long goat-like legs and a heavy sheep-like body. Although infertile, the hybrid had a very active libido, mounting both ewes and does even when they were not in heat. He was castrated when he was 10 months old, as were the other kids and lambs in the herd.
A male sheep impregnated a female goat in New Zealand resulting in a mixed litter of kids and a female sheep–goat hybrid with 57 chromosomes. The hybrid was subsequently shown to be fertile when mated with a ram.
Chicken-Guineafowl hybrids are often cited as interbreeding between different families (though they are in the same Superfamily). I suppose different parts of the Tree of Life have different relationships between taxonomic grading and genetic distance.
Manatees and Seals, on the other hand, are in different Orders: As Elixir states, Manatees are in Order Sirenea, sibling to Order Proboscidea (elephants), while Seals are closely related to bears and wolves which, with Cats, form Order Carnivora. Sirenea and Carnivora are in different Legions (see list above). The earliest division in placental mammals may have been between two groups associated with Gondwana and Laurasia supercontinents; these groups include Sirenea and Carnivora respectively.