Bag cell peptides (BCPs) are a class of small neuropeptides secreted by the bag cell neurons in the marine mollusk Aplysia1. They trigger a series of reproductive behavior in this mollusk that finally culminates in egg-laying1.

BCPs were originally identified in the bag cell extracts of abdominal ganglion of mature Aplysia that were obtained in Venice, CA2. They were isolated based on their ability to cause bag cell excitation2.

Bag cell specific gene that encodes for the precursor form of the egg laying hormone also contains sequences that encode several small BCPs: a-BCP, b-BCP, g-BCP2, d-BCP3,4 and e-BCP5.