A tubular structure in Velella velella, probably with a digestive function.

[Mollusca] The mantle structure through which water (rarely air) can flow in and out of the mantle cavity.

[Crustacea: Ostracoda] An inhalant respiratory flow of water enters through the gap between the carapace valves at the incisure, passes over the body and discharges through a siphon on the posterior margin (Ostracoda: diagram of respiratory flow).