It is kind of hard to tell bet once you see it you will understand.
Shelmet is a knight's helmet combined with a snail.
![Shelmet](https://cdn.bulbagarden.net/upload/thumb/f/f6/616Shelmet.png/250px-616Shelmet.png)
![Helmet](/pokebase/qa-plugin/https-img-proxy/image.php?key=ebe7538293509c24&url=http%3A%2F%2Fwww.swordsandarmor.com%2Fimages%2FH002203_White_Knight_Helmet.JPG)
Karrablast is based off of the Japanese Snail-eating Beetle.
![Karrablast](https://cdn.bulbagarden.net/upload/thumb/6/60/588Karrablast.png/250px-588Karrablast.png)
![Beetle](https://myrmecos.files.wordpress.com/2008/02/scaphinotus5.jpg)
Accelgor is rather hard to explain but Bulbapedia explains it perfectly.
>Accelgor appears to be based on an auto racer or a ninja, combined with a giant tube worm. Its cloth-like "clothing" and Bug type suggest it may also be based on the bagworm pupa.
![Accelgor](https://cdn.bulbagarden.net/upload/thumb/3/34/617Accelgor.png/250px-617Accelgor.png)
![Giant Tube Worm](https://40.media.tumblr.com/tumblr_lyupmyOfej1qaj00vo1_500.jpg)
Escavalier is also based off of the Japanese Snail-eating Beetle but it is combined with a jousting knight.
![Escavalier](https://cdn.bulbagarden.net/upload/thumb/6/63/589Escavalier.png/250px-589Escavalier.png)
![Knight](https://slm-assets2.secondlife.com/assets/1539883/lightbox/874e911e6cd802e21e7d67412af443ae.jpg?1277246595)
Hope I helped!
Sources:
Source1
Source2
Source3
Source4
And knowledge
(Sorry for the big pictures.)