Ultrastructural Features of Gut Regeneration in Five-Month-Old Pentactulae of the Holothurian Eupentacta fraudatrix

Posterior regeneration of the digestive system after bisection was investigated in the anterior halves of the five-month-old pentactulae of the holothurian Eupentacta fraudatrix using electron microscopy. Three stages of gut restoration were distinguished. The first stage is characterized by degradation of the damaged part of the gut followed by wound healing. Active morphogenetic processes (cell proliferation, dedifferentiation, cell migration, and redifferentiation) are observed at the second stage. During the third (final) stage, the ablated parts differentiate in the posterior portion of the intestine. The cells of the gut remnant tissues were shown to be the cell sources of regeneration. Based on both the data available from the literature and the results of our study, the conclusion was drawn that the mechanisms of gut restoration differ significantly in the pentactulae and adults of E. fraudatrix.