External anatomy of sea squirt. It is secreted by the epidermis of the body wall. The larva and adult have a mucus-secreting gland, the endostyle, that is…. It is connected to the digestive system at one end and to the inhalant siphon at the other, this is effectively the animal's mouth. The cloaca opens to the exterior through atrial siphon and trial aperture. Red sea squirt. You've done a great job! It is single layer of flat cells. Although all adults are simultaneous hermaphrodites possessing both male and female functional reproductive organseggs shed into the water are fertilized by sperm from other individuals. The biochemical function of hemovanadin, a strong reducing agent, is unknown. Red sea squirt.