FORMATION OF THE TEST IN THE SWIMMING LARVA OF CIONA-INTESTINALIS - AN ULTRASTRUCTURAL-STUDY

  • 1 January 1984
    • journal article
    • research article
    • Vol. 16  (2) , 289-297
Abstract
The test of the C. intestinalis larva, before hatching, presents a single outer cuticular layer, C1. Ultrastructural observations of swimming larvae, kept in culture at 18.degree. C, show that the test is enriched by a 2nd inner cuticular layer C2. The C2 layer begins to form in the larva immediately after hatching (about 1 h) and is a process caused by the activity of the cells of the ectodermal layer. During this phase of larval development, these cells assume the typical ultrastructure of cells with secretory activity, presenting a well developed rer [rough endoplasmic reticulum] and a Golgi in the form of dictyosomes in active synthesis phase in the apical zone of their cytoplasm. The formation of C2 layer is complete in the larva 3 h after hatching and in this period it can be seen parallel to, and a short distance from, the plasmalemma of the ectodermal cells. In the cephalenteron region, the C2 layer progressively rises towards the C1 layer and, in the larva 8 h after hatching, these 2 layers are very close together, about 1000 .ANG. apart. The C2 layer in the tail remains close to the plasmalemma of the ectodermal cells and can only be detected by ultrastructural observations.

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