Snap just threw shade at Instagram in its IPO filing

Three years after rejecting an acquisition offer from , Snap CEO Evan Spiegel is tossing some insults at the company's Instagram unit.

"Instagram, a subsidiary of Facebook, recently introduced a 'stories' feature that largely mimics our Stories feature and may be directly competitive," Snap said on Thursday in the "Risk Factors" section of its IPO filing.

Stories are groups of snaps that are collected by users and can be viewed by friends. They started as tools for consumers and are now also used by advertisers. While Instagram Stories has grown fast, it hasn't cut into Snapchat's popularity, according to research firm AppAnnie, and ad buyers told CNBC they're still enthusiastic about Snapchat, which has some features for advertisers that Instagram still lacks.

Additionally, Snap referenced an advertising report from September 2016, that ranked the top online ad platforms. The company said that in a comparison to Facebook, Instagram and other competitors like and , "we ranked first in overall satisfaction," even if advertisers had plans to spend more money elsewhere.

Overall, Snap is still way behind Facebook. According to eMarketer, Facebook will command 15 percent of the digital ad market this year, second to Google, which controls 32 percent. Snap is tied for 14th globally at 0.4 percent.

While Facebook, Google and Twitter are obvious competitors to Snap, the company included a more surprising rival in its risks section: . Snap said it competes with iPhone maker's social media offerings, though as Snap moves deeper into hardware with Spectacles glasses, it seems more likely that it will be turn into a wearables battle.