THE METHOD OF FEEDING OF TUNICATES

¹ From the William G. Kerckhoff Marine Laboratory of the California Institute of Technology

1. The feeding method of Ciona intestinalis and Ascidia californica (simple ascidians), and of Diplosoma pizoni (a colonial form) was investigated.

2. Tunicates feed by straining the solid material from a current of water as it passes through a thin film of mucus lining the branchial basket.

3. The mucus is constantly secreted at the endostyle and is continually moved to the dorsal groove in two sheets which line the interior of the basket. The dorsal groove forms the edges of the food-laden sheets into a thread which is passed posteriorly to the esophagus and enters it in an unbroken string. The peripharyngeal grooves serve to hold the anterior ends of the mucous sheets and move them around to the dorsal groove.

4. When a tunicate is not feeding, the inside of the branchial basket is not lined with mucus, and the solid materials pass out with the atrial current.

5. Some sorting is carried out by the cilia of the dorsal ridges. The cilia which line the openings of the stigmata, and whose vibration creates the current of water passing through the basket, may be stopped without stopping the cilia lining the basket or without closure of the oral aperture and atriopore.

6. After the cilia lining the stigmata have been stopped they commence to beat in what appears to be a ring at the center of the opening. The cilia of one side of a stigmata are in perfect synchronism with those of the opposite side of the opening, and, by the continual inclusion of other cilia, all finally vibrate and resemble somewhat an elongated wheel organ of a rotifer.

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