Ventilation in respiratory tree of the Japanese common sea cucumber, Apostichopus japonicus

Ventilation in the respiratory tree of the Japanese common sea cucumber, Apostichopus japonicus was analyzed by modeling the movements of the aloaca and the coelom as the double-pumping system based on the continuous records of the ventilation volume and the inner pressures of the cloaca and coelom. The sequence of ventilation phases is regarded as follows: 1) The boundary between the respiratory tree and the cloaca is closed. The anus is opened and the sea-water is inhaled into the enlarged cloaca. 2) The cloaca is expanded and the inner pressure of the coelom is elevated. The volume of the coelom is increased by the increasing inner pressure of the coelom. 3) The anus is closed and the boundary is opened. The sea-water is injected from the cloaca into the respiratory tree by contracting the cloaca. The inner pressure of the coelom does not change because the sea-water is simply moved in the coelom. 4) The volume of the coelom is increased with repeating the sequence of ventilation from phase 1 to phase 3 (inhalation) and subsequently the ventilation is temporarily stopped. 5) The inner pressure of the coelom is elevated with increasing the volume of the respiratory tree by repeating inhalation. The anus and the boundary are opened and the sea-water in the respiratory tree and the cloaca is once exhaled by the elastic force of the body wall without the contraction force of the body wall and/or the cloaca.