Если серьёзно, то конечно, просто hippo. Нет у них родовых суффиксов-окончаний, ну что поделать. И не надо, имя на себя возьмёт нужные функции.

Но чтоб вот так запросто на ужин в кухню бегемот являлся - такого не видел раньше никогда.

The Hippopotamus Song
http://www.youtube.com/watch?v=AjnOj9O16_I

A bold hippopotamus was standing one day
On the banks of the cool Shalimar
He gazed at the bottom as he peacefully lay
By the light of the evening star
Away on the hilltop sat combing her hair
His fair hippopotami maid
The hippopotamus was no ignoramus
And sang her this sweet serenade

Chorus:
Mud, mud, glorious mud
Nothing quite like it for cooling the blood
So follow me follow, down to the hollow
And there let me wallow in glorious mud
The fair hippopotama he aimed to entice
From her seat on that hilltop above
As she hadn't got a ma to give her advice
Came tiptoeing down to her love
Like thunder the forest re-echoed the sound
Of the song that they sang when they met
His inamorata adjusted her garter
And lifted her voice in duet