Quarterly Journal of Microscopical Science, Vol s3-102, 107-117, Copyright © 1961 by Company of Biologists

The Test of the Ascidian, Phallusia mammillata

¹ Department of Zoology, University of Queensland

A mucopolysaccharide, readily removed by mild acid hydrolysis, is associated with cellulose in the test of Phallusia mammillata (Cuvier). The mucopolysaccharide is produced in the vacuolated cytoplasm of epidermal cells covering theblood-vessels of the test.

The cellulose of the test appears to be produced by vanadocytes which have migrated into the test matrix through the walls of the test blood-vessels. In the test, the vanadocytes lose their acid and intraglobular osmiophil material and produceprocesses which extend into the surroundin g test matrix. Minut e globules and submicroscopic vesicles are present in the cytoplasm surrounding the large polysaccharide-containing globules of such vanadocytes, and also in the processes arising from such cells. The small globules and vesicles appear to arise from the large globules and to be involved in the productio n of micro-fibrils observed in electron micrographs of the test. The micro-fibrils, which vary fro m 20 to 40 mµ indiameter and are arranged in the form of an open network, may constitute a cellulose framework within the test.

An area devoid of test matrix occurs usually near each disintegrating vanadocyte. The remnants of each vanadocyte often come to lie in such an area. Capsules--the so-called ‘bladder cells’ of the test are thereby formed.

Phagocytes occur throughout the test and melanin-containing pigment cells are aggregated around its periphery.