Autotomy and regeneration of the visceral mass in feather stars

Abstract

The morphology of the visceral mass and the ability to eviscerate and regenerate internal organs were studied in 15 species of feather stars belonging to the superfamilies Himerometroidea and Comatuloidea. It was shown that members of various families differ in the structure of the visceral mass, mode and strength of its attachment to the calyx, presence or absence of autotomy, and rate of regeneration. In all the studied species of Himerometroidea, the secondary body cavity is divided into subintestinal and aboral coeloms. The gut is separated from the calyx by a connective tissue layer that forms the aboral wall of the subintestinal coelom. The Himerometroidea exhibit the ability to autotomise and rapidly regenerate the visceral mass. They form a new digestive system, including mouth and anal cone, within 4 days after damage. All the studied species of Comatuloidea have a different visceral mass structure and lack the ability to autotomise internal organs. In this superfamily, species differ in tegmen thickness, which probably affects the ease of visceral mass removal. New gut formation in Comatuloidea is slower than in Himerometroidea and takes from 10 to 25 days depending on species. This can probably be explained by the greater damage to the calyx surface during removal of the visceral mass and by differences in regeneration mechanisms. In all the studied species of feather stars, juxtaligamental cells were found in the septa of the intestinal coelom and tegmen. The morphology and distribution pattern of these cells are species specific. It is suggested that the differences in the number, localization, and innervation of the juxtaligamental cells correlate with the presence or absence of the ability to autotomise the visceral mass and the means of regeneration.