This is called a Mermaid's Purse:
The cords you see attached to barnacles is actually the umbilical cord.
Mermaids purses are the eggs of select species of shark.
They come in many forms and are very unusual. The below is from a ghost shark:
Named after its ghostly appearance, lacking vision and living far too deep to be reached by sunlight.
Sharks typically drop their mermaid purses in pairs in secure areas on the ocean floor, in kelp or in rocky crevices to avoid notice of predators.
Catshark egg:
And cat shark embryo- later in development: