Some other animals in Pokémon artworks (list taken from here - I’ve excluded the mentioned ‘shark’ in Super Rod, since that’s a Magikarp):
Bird on top of Weepinbell:
Bug in front of Bulbasaur’s toe:
Frog next to Oddish (never noticed this one myself before 
):
Wasp near Venonat (I also didn’t knew about this one prior):
Butterfly on top of Squirtle’s tail:
Butterflies around Eevee:
Worm-bait for Magikarp:
Worm underneath Spearow:
Crab next to Exeggutor:
Sea anemones next to Wooper:
Butterflies and fish around Slowpoke:
Fish/porpoise near Magikarp (a bit hard to see):
Coral next to Horsea:
Coral and sea anemone below Quagsire:
Coral behind Luvdisk:
I think there are more artworks with coral / sea anemones not in the list, though… Will see if I can find a few more later on.
Greetz,
Quuador