21. The bivalve's two siphons are situated at the posterior edge of the mantle cavity . 22. There are no gills; the entire surface of the mantle cavity absorbs oxygen from the water. 23. The cilia of the lophophore generate a feeding and respiratory current through the lophophore and mantle cavity . 24. The outer palps send this rejected material into the mantle cavity as a mucus-bound mass. 25. Inside the mantle cavity the animal has a highly vascularized area of tissue that functions as a lung. 26. The mantle cavity acts as a lung cavity . The taenioglossan radula has seven elements per transverse row. 27. The mantle cavity is divided into two chambers by ctenidia that circulate water and waste through the chiton. 28. However, the ink is not released, instead it is retained inside the now spherical mantle cavity . 29. Water enters the mantle cavity through the apical aperture, and is wafted along the body surface by cilia. 30. Air enters through the pneumostome into the animal's single lung, the air-filled mantle cavity .
