They are treats that are made for amoebas and come in a pale brown paper bag that depicts the word "amoeba" in dark red text and the word "treats" in bluish-purple text bordered by a red outline. Below the text is an illustration of the food inside, which are those white bone-shaped treats.
Role in episode
After Plankton examines his pet amoeba, Spot, with an X-ray, he is shocked to find out that Spot is pregnant, assuming he was a boy. Karen points out that it does not matter since the provision of food-rich environments causes amoebas to reproduce. The scene then pans to all of the food Plankton has been feeding to Spot, one of them being the Amoeba Treats.
Towards the end, after Plankton's attempt to steal the Krabby Pattysecret formula by using Spot's children to gain possession of it fails, SpongeBob pours a bag of Amoeba Treats on Plankton as revenge for trapping him in a cage, which attracts several of the children and increases their size.