it is wormadam and can be found on route 214 in a trainer's party.
According to the serebii.net pokedex you can get it in the safari game. (If you are talking about National Pokedex number 46, which is Paras).
45=burmy 46=wormadam
on the sinnoh pokedex its the Pokemon wormadam
Paras
Wormadon. Wormadon Is the number 46 on Pokemon diamon
45 is Burmy and you can get it by putting honey onto a honey tree.
Number 46 is a WORMADAM. If you want to find one I'm afraid i don't know where to get one.
Wormadam It can be found in Route 214 A Trainer that's a girl with blonde hair (Behind a fence Easy to avoid Her)
Pokemon #46 is Wormadam. If you need any other help go to www.pokemon.marriland.com On the side in the diamond and pearl section it has a pokedex option, click there and you will see all the pokemon.
Its Wormadan... And in the pokedex doesnt appears... I guess you'll find a trainer later on who has ir.... unless you catch a burmy... it evolves into a Wormadan
wormadam
wormadam