Pokémon that evolve into different Body Styles

http://bulbapedia.bulbagarden.net/wiki/List_of_Pok%C3%A9mon_by_body_style#Pok.C3.A9mon_with_an_insectoid_body

Pokémon consisting of only a body:

1. Gastly->Haunter(Pokémon consisting of a head and arms)->Gengar(Pokémon with a bipedal, tailed form)
2. Koffing->Weezing(Pokémon consisting of multiple bodies)
3. Sunkern->Sunflora(Pokémon with a bipedal, tailless form)
4. Silcoon->Beautifly(Pokémon with two or more pairs of wings)
5. Cascoon->Dustox(Pokémon with two or more pairs of wings)
6. Shuppet->Banette(Pokémon with a bipedal, tailed form)
7. Clamperl->Huntail/Gorebyss(Pokémon with serpentine bodies)
8. Bronzor->Bronzong(Pokémon consisting of a head and arms)
9. Whirlipede->Scolipede(Pokémon with an insectoid body)
10. Cottonee->Whimsicott(Pokémon with a bipedal, tailless form)
11. Solosis-Duosion->Reuniclus(Pokémon consisting of a head and arms)
12. Pumpkaboo->Gourgeist(Pokémon consisting of a head and a base)
13. Cosmog->Cosmoem->Solgaleo(Pokémon with a quadruped body)/Lunala(Pokémon with a single pair of wings)

Pokémon with serpentine bodies:

1. Metapod->Butterfree(Pokémon with two or more pairs of wings)
2. Kakuna->Beedrill(Pokémon with two or more pairs of wings)
3. Dratini->Dragonair->Dragonite(Pokémon with a bipedal, tailed form)
4. Goomy->Sliggoo->Goodra(Pokémon with a bipedal, tailed form)

Pokémon with fins:

1. Magikarp->Gyarados(Pokémon with serpentine bodies)
2. Remoraid->Octillery(Pokémon with tentacles or a multiped body)
3. Feebas->Milotic(Pokémon with serpentine bodies)
4. Sealeo->Spheal->Walrein( Pokémon with a quadruped body)
5. Tympole->Palpitoad(Pokémon with a bipedal, tailed form)->Seismitoad(Pokémon with a bipedal, tailless form)

Pokémon consisting of a head and arms:

1. Geodude->Graveler(Pokémon with a bipedal, tailless form)->Golem(Pokémon with a bipedal, tailless form)
2. Magnemite->Magneton(Pokémon consisting of multiple bodies)->Magnezone(Pokémon consisting of a head and arms)
3. Spoink->Grumpig(Pokémon with a bipedal, tailed form)
4. Duskull->Dusclops(Pokémon with a bipedal, tailless form)->Dusknoir(Pokémon consisting of a head and arms)
5. Yamask->Cofagrigus(Pokémon consisting of a head and a base)
6. Spritzee->Aromatisse(Pokémon with a bipedal, tailless form)
7. Phantump->Trevenant(Pokémon with tentacles or a multiped body)

Pokémon consisting of a head and a base:

1. Diglett->Dugtrio(Pokémon consisting of multiple bodies)
2. Beldum->Metang(Pokémon consisting of a head and arms)->Metagross(Pokémon consisting of multiple bodies)
3. Vanillite->Vanillish->Vanilluxe(Pokémon consisting of multiple bodies)
4. Litwick->Lampent(Pokémon consisting of a head and arms)->Chandelure(Pokémon consisting of a head and arms)
5. Honedge->Doublade(Pokémon consisting of multiple bodies)->Aegislash(Pokémon consisting of a head and a base)
6. Mareanie->Toxapex(Pokémon with tentacles or a multiped body)
7. Morelull->Shiinotic(Pokémon with a bipedal, tailless form)

Pokémon with a bipedal, tailed form:

1. Abra->Kadabra->Alakazam(Pokémon with a bipedal, tailless form)
2. Machop->Machoke(Pokémon with a bipedal, tailless form)->Machamp(Pokémon with a bipedal, tailless form)
3. Lickitung->Lickilicky(Pokémon with a bipedal, tailless form)
4. Larvitar->Pupitar(Pokémon with serpentine bodies)->Tyranitar(Pokémon with a bipedal, tailed form)
5. Wynaut->Wobbuffet(Pokémon consisting of a head and a base)
6. Snivy->Servine->Serperior(Pokémon with serpentine bodies)
7. Oshawott->Dewott->Samurott(Pokémon with a quadruped body)
8. Drilbur->Excadrill(Pokémon with a bipedal, tailless form)
9. Elgyem->Beheeyem(Pokémon with a bipedal, tailless form)
10. Cubchoo->Beartic(Pokémon with a quadruped body)
11. Pancham->Pangoro(Pokémon with a bipedal, tailless form)
12. Fomantis->Lurantis(Pokémon with a bipedal, tailless form)

Pokémon consisting of a head and legs:

1. Oddish->Gloom(Pokémon with a bipedal, tailless form)->Vileplume(Pokémon with a bipedal, tailless form)/Bellossom(Pokémon with a bipedal, tailless form)
2. Poliwag->Poliwhirl(Pokémon with a bipedal, tailless form)->Poliwrath(Pokémon with a bipedal, tailless form)/Politoed(Pokémon with a bipedal, tailless form)
3. Tangela->Tangrowth(Pokémon with a bipedal, tailless form)s
4. Porygon->Porygon2->Porygon-Z(Pokémon consisting of a head and arms)
5. Wooper->Quagsire(Pokémon with a bipedal, tailed form)
6. Torchic->Combusken(Pokémon with a bipedal, tailed form)->Blaziken(Pokémon with a bipedal, tailed form)
7. Seedot->Nuzleaf(Pokémon with a bipedal, tailless form)->Shiftry(Pokémon with a bipedal, tailless form)
8. Shroomish->Breloom(Pokémon with a bipedal, tailed form)
9. Azurill->Marill(Pokémon with a bipedal, tailed form)->Azumarill(Pokémon with a bipedal, tailed form)
10. Bonsly->Sudowoodo(Pokémon with a bipedal, tailless form)
11. Roggenrola->Boldore(Pokémon with tentacles or a multiped body)->Gigalith(Pokémon with tentacles or a multiped body)
12. Swirlix->Slurpuff(Pokémon with a bipedal, tailless form)
13. Dewpider->Araquanid(Pokémon with insectiod bodies)
14. Bounsweet->Steenee(Pokémon with a bipedal, tailless form)->Tsareena(Pokémon with a bipedal, tailless form)

Pokémon with a quadruped body:

1. Pichu->Pikachu->Raichu(Pokémon with a bipedal, tailed form)
2. Nidoran♀->Nidorina->Nidoqueen(Pokémon with a bipedal, tailed form)
3. Nidoran♂->Nidorino->Nidoking(Pokémon with a bipedal, tailed form)
4. Slowpoke->Slowbro/Slowking(Pokémon with a bipedal, tailed form)
5. Rhyhorn->Rhydon(Pokémon with a bipedal, tailed form)->Rhyperior(Pokémon with a bipedal, tailed form)
6. Mareep->Flaaffy(Pokémon with a bipedal, tailed form)->Ampharos(Pokémon with a bipedal, tailed form)
7. Slakoth->Vigoroth(Pokémon with a bipedal, tailed form)->Slaking(Pokémon with a bipedal, tailless form)
8. Aron->Lairon->Aggron(Pokémon with a bipedal, tailed form)
9. Bidoof->Bibarel(Pokémon with a bipedal, tailed form)
10. Tepig->Pignite(Pokémon with a bipedal, tailed form)->Emboar(Pokémon with a bipedal, tailed form)
11. Patrat->Watchog(Pokémon with a bipedal, tailed form)
12. Munna->Musharna(Pokémon with a bipedal, tailless form)
13. Sandile->Krokorok->Krookodile(Pokémon with a bipedal, tailed form)
14. Tirtouga->Carracosta(Pokémon with a bipedal, tailed form)
15. Zorua->Zoroark(Pokémon with a bipedal, tailed form)
16. Deino->Zweilous->Hydreigon(Pokémon with a bipedal, tailed form)
17. Fennekin->Braixen(Pokémon with a bipedal, tailed form)->Delphox(Pokémon with a bipedal, tailed form)
18. Froakie->Frogadier(Pokémon with a bipedal, tailless form)->Greninja(Pokémon with a bipedal, tailless form)
19. Litten->Torracat->Incineroar(Pokémon with a bipedal, tailed form) 
20. Rockruff->Lycanroc Midnight Form(Pokémon with a bipedal, tailed form)
21. Stufful->Bewear(Pokémon with a bipedal, tailed form)
22. Jangmo-o->Hakamo-o(Pokémon with a bipedal, tailed form)->Kommo-o(Pokémon with a bipedal, tailed form)

Pokémon with a single pair of wings:

1. Zubat->Golbat->Crobat(Pokémon with two or more pairs of wings)

Pokémon with tentacles or a multiped body:

1. Inkay->Malamar(Pokémon consisting of a head and a base)
2. Wimpod->Golisopod(Pokémon with a bipedal, tailless form)

Pokémon consisting of multiple bodies:

1. Exeggcute->Exeggutor(Pokémon consisting of a head and legs)
2. Combee->Vespiquen(Pokémon with two or more pairs of wings)
3. Cherubi->Cherrim(Pokémon consisting of a head and legs)

Pokémon with a bipedal, tailless form:

1. Venonat->Venomoth(Pokémon with two or more pairs of wings)
2. Bellsprout->Weepinbell(Pokémon consisting of a head and a base)->Victreebel(Pokémon consisting of a head and a base)
3. Cyndaquil->Quilava(Pokémon with a quadruped body)->Typhlosion(Pokémon with a quadruped body)
4. Snubbull->Granbull(Pokémon with a bipedal, tailed form)
5. Tyrogue->Hitmontop(Pokémon with a bipedal, tailed form)
6. Elekid->Electabuzz(Pokémon with a bipedal, tailed form)->Electivire(>Pokémon with a bipedal, tailed form)
7. Nosepass->Probopass(Pokémon consisting of multiple bodies)
8. Snorunt->Glalie(Pokémon consisting of only a head)/Froslass(Pokémon consisting of a head and arms)
9. Bagon->Shelgon(Pokémon with a quadruped body)->Salamence(Pokémon with a quadruped body)
10. Piplup->Prinplup(Pokémon with a bipedal, tailed form)->Empoleon(Pokémon with a bipedal, tailed form)
11. Kricketot->Kricketune(Pokémon with two or more pairs of wings)
12. Chingling->Chimecho(Pokémon consisting of a head and arms)
13. Darumaka->Darmanitan(Pokémon with a quadruped body)
14. Karrablast->Escavalier(Pokémon consisting of a head and arms)

Pokémon with an insectoid body:

1. Caterpie->Metapod(Pokémon with serpentine bodies)->Butterfree(Pokémon with two or more pairs of wings)
2. Weedle->Kakuna(Pokémon with serpentine bodies)->Beedrill(Pokémon with two or more pairs of wings)
3. Kabuto->Kabutops(Pokémon with a bipedal, tailed form)
4. Wurmple->Cascoon/Silcoon(Pokémon consisting of only a head)-Beautifly/Dustox(Pokémon with two or more pairs of wings)
5. Lotad-Lombre(Pokémon with a bipedal, tailless form)->Ludicolo(Pokémon with a bipedal, tailless form)
6. Surskit->Masquerain(Pokémon with two or more pairs of wings)
7. Nincada->Ninjask(Pokémon with two or more pairs of wings)/Shedinja(Pokémon consisting of a head and a base)
8. Trapinch->Vibrava(Pokémon with two or more pairs of wings)->Flygon(Pokémon with a single pair of wings)
9. Anorith->Armaldo( Pokémon with a bipedal, tailed form)
10. Sewaddle->Swadloon(Pokémon consisting of a head and arms)->Leavanny(Pokémon with a bipedal, tailless form)
11. Larvesta->Volcarona(Pokémon with two or more pairs of wings)
12. Scatterbug->Spewpa(Pokémon consisting of a head and a base)
13. Clauncher->Clawitzer(Pokémon with serpentine bodies)
14. Grubbin->Charjabug(Pokémon with serpentine bodies)->Vikavolt
15. Cutiefly->Ribombee(Pokémon with two or more pairs of wings)

Pokémon whose body styles remain the same:

Pokémon consisting of only a body:

1. Shellder-Cloyster
2. Voltorb-Electrode
3. Mismagius->Misdreavus
4. Pineco->Forretress

Pokémon with serpentine bodies

1. Ekans->Arbok
2. Onix->Steelix
3. Shellos-> Gastrodon
4. Sandygast->Pallosand

Pokémon with fins:

1. Seel->Dewgong
2. Goldeen->Seaking
3. Chinchou->Lanturn
4. Carvanha->Sharpedo
5. Wailmer->Wailord
6. Barboach->Whiscash
7. Finneon->Lumineon
8. Tynamo->Eelektrik->Eelektross
9. Popplio->Brionne->Primarina

Pokémon consisting of a head and arms:

1. Grimer->Muk
2. Gulpin->Swalot
3. Baltoy->Claydol
4. Drifloon->Drifblim
5. Foongus->Amoonguss
6. Flabébé->Floette->Florges

 Pokémon consisting of a head and a base:

1. Horsea->Seadra->Kingdra
2. Staryu->Starmie
3. Lileep->Cradily
4. Burmy->Wormadam
5. Petilil->Lilligant
6. Skrelp->Dragalge

Pokémon with a bipedal, tailed form:

1. Charmander->Charmeleon->Charizard
2. Squirtle->Wartortle->Blastoise
3. Sandshrew->Sandslash
4. Cleffa->Clefairy->Clefable
5. Psyduck->Golduck
6. Mankey->Primeape
7. Cubone->Marowak
8. Totodile->Croconaw->Feraligatr
9. Hoppip->Skiploom->Jumpluff
10. Aipom->Ambipom
11. Sneasel->Weavile
12. Teddiursa->Ursaring
13. Magby->Magmar->Magmortar
14. Treecko->Grovyle->Sceptile
15. Whismur->Loudred->Exploud
16. Chimchar->Monferno->Infernape
17. Cranidos->Rampardos
18. Buneary->Lopunny
19. Gible->Gabite->Garchomp
20. Riolu->Lucario
21. Snover->Abomasnow
22. Pansage->Simisage
23. Pansear->Simisear
24. Panpour->Simipour
25. Scraggy->Scrafty
26. Axew->Fraxure->Haxorus
27. Mienfoo->Mienshao
28. Chespin->Quilladin->Chesnaught
29. Bunnelby->Diggersby
30. Espurr->Meowstic
31. Helioptile->Heliolisk
32. Tyrunt->Tyrantrum

Pokémon consisting of a head and legs:

1. Doduo->Dodrio

Pokémon with a quadruped body:

1. Bulbasaur->Ivysaur->Venusaur
2. Rattata-> Raticate
3. Vulpix->Ninetales
4. Meowth->Persian
5. Growlithe->Arcanine
6. Ponyta-> Rapidash
7. Eevee->Vaporeon/Jolteon/Flareon/Espeon/Umbreon/Glaceon/Leafeon/Sylveon
8. Chikorita->Bayleef ->Meganium
9. Sentret->Furret
10. Swinub->Piloswine->Mamoswine
11. Houndour->Houndoom
12. Phanpy->Donphan
13. Poochyena->Mightyena
14. Zigzagoon->Linoone
15. Skitty->Delcatty
16. Electrike->Manectric
17. Numel->Camerupt
18. Turtwig->Grotle->Torterra
19. Shinx->Luxio->Luxray
20. Shieldon->Bastiodon
21. Buizel->Floatzel
22. Glameow->Purugly
23. Stunky->Skuntank
24. Hippopotas->Hippowdon
25. Lillipup->Herdier->Stoutland
26. Purrloin->Liepard
27. Blitzle->Zebstrika
28. Minccino->Cinccino
29. Deerling->Sawsbuck
30. Litleo->Pyroar
31. Skiddo->Gogoat
32. Amaura->Aurorus
33. Bergmite ->Avalugg
34. Yungoos->Gumshoos
35. Rockruff->Lycanroc Midday Form
36. Mudbray->Mudsdale
37. Salandit->Salazzle
38. Type: Null->Silvally

Pokémon with a single pair of wings:

1. Pidgey->Pidgeotto->Pidgeot
2. Spearow->Fearow
3. Zubat->Golbat
4. Hoothoot ->Noctowl
5. Ledyba->Ledian
6. Natu ->Xatu
7. Murkrow->Honchkrow
8. Gligar->Gliscor
9. Mantine->Mantyke
10. Taillow->Swellow
11. Wingull->Pelipper
12. Swablu->Altaria
13. Starly->Staravia->Staraptor
14. Pidove->Tranquill->Unfezant
15. Woobat->Swoobat
16. Archen->Archeops
17. Ducklett->Swanna
18. Rufflet->Braviary
19. Vullaby->Mandibuzz
20. Fletchling->Fletchinder->Talonflame
21. Noibat->Noivern
22. Rowlet->Dartrix->Decidueye
23. Pikipek->Trumbeak->Toucannon

Pokémon with tentacles or a multiped body:

1. Tentacool->Tentacruel
2. Omanyte->Omastar
3. Frillish->Jellicent

Pokémon consisting of multiple bodies:

1. Klink->Klang->Klinklang
2. Binacle->Barbaracle

Pokémon with a bipedal, tailless form:

1. Jigglypuff->Wigglytuff->Igglybuff
2. Drowzee->Hypno
3. Tyrogue->Hitmonlee
4. Tyrogue->Hitmonchan
5. Mime Jr.->Mr. Mime
6. Smoochum->Jynx
7. Munchlax->Snorlax
8. Ralts->Kirlia->Gardevoir/Gallade
9. Makuhita->Hariyama
10. Meditite->Medicham
11. Cacnea->Cacturne
12. Budew->Roselia->Roserade
13. Croagunk ->Toxicroak
14. Timburr->Gurdurr->Conkeldurr
15. Trubbish->Garbodor
16. Gothita->Gothorita->Gothitelle
17. Golett->Golurk
18. Pawniard->Bisharp

Pokémon with two or more pairs of wings:

1. Scyther->Scizor
2. Yanma->Yanmega

Pokémon with an insectoid body:

1. Paras->Parasect
2. Krabby->Kingler
3. Spinarak->Ariados
4. Corphish->Crawdaunt
5. Skorupi->Drapion
6. Dwebble->Crustle
7. Joltik->Galvantula 
8. Crabrawler->Crabominable

Edit(11.01.2017): Added Gen VII additions.
Edit (31.12.2019): Cleaned up. This category no longer exists in Gen 8 Pokédex, so no new additions are listed.