Resemblance: a way in which two or more things are alike.
They look alike to me.
It is also possible that Blastoise is BASED off of Gamera.
According to Wikipedia, Gamera, the Giant Monster was released in Japan in 1965.
Pokemon was released in 1996 according to Bulbapedia, also in Japan.
This means that Gamera existed before Blastoise, and could have influenced its design.
Gamera was originally created as competition to Godzilla's success, and Gamera has won some fame for itself. Blastoise could very well be GameFreak's tribute to Gamera and popular culture.
This is all just speculation. There doesn't appear to be any proof for a link between Gamera and Blastoise.
On Bulbapedia, on the Talk:Blastoise (Pokémon) page under the Gamera heading they say:
For Blastoise's origin, isn't he based off Gamera (giant turtle in Japanese monster movies)too?
Response: Other than being a turtle, Blastoise and Gamera share NO similarities whatsoever.
I'm naming my next Blastoise Gamera.