his hedgehog's name is Sebastian, is not related to Sonic the Hedgehog,
more on hedgehogs in literature.
No, hedgehogs are not related to porcupines or echidnas.
Then there are the hedgehog genes
The first two discovered, desert hedgehog and Indian hedgehog, were named for species of hedgehogs, while sonic hedgehog was named after Sega's video game character Sonic the Hedgehog. In zebrafish, the orthologues of the three mammalian hh genes are: shh a, shh b, (formerly described as tiggywinkle hedgehog named for Mrs. Tiggy-Winkle, a character from Beatrix Potter's books for children), and indian hedgehog b (formerly described as echidna hedgehog, named for the spiny anteater, though this may have also been a playful reference to Knuckles the Echidna, another character from the Sonic the Hedgehog series of video games).
Sebastian is the name of the Teddy Bear in Brideshead...
Best line in the film:
“Those are Gundobad Wargs. They’ll catch and eat you.”
“These are Rhosgobel Rabbits. I’d like to see them try.”