A comparative study of gut mucous cells in thirty-seven species of the class Echinoidea (Echinodermata).

Abstract

The gut of echinoids is lined by an epithelium which includes some mucous cells ; the structure and function of echinoid guts in general has recently been reviewed by Anderson ( 1966) . The term mucous cell is restricted in the present paper to denote only those epithelial cells containing a conspicuous accumulation of mucus intracellularly. In addition, the lining epithelium of echinoid guts may include the following two kinds of cells associated with mucus, yet not considered here to be mucous cells : ( 1) mucus-containing coelomocytes wandering in the gut wall and (2) epithelial cells lacking intracellular mucus, but having a thin glyco calyx of mucus associated with the distal cell membrane. Mucous cells in echinoid guts were first mentioned explicitly by Koehler in 1883; unfortunately, his report is hard to evaluate, because it came long before the advent of histo chemistry. Since the development of histochemical methods for mucopolysac charides, gut mucous cells have been studied in some detail for the following echinoid species: Echinus esculentus (Stott, 1955; Buchanan, 1969), Strongylo centrotus intermedius (Fuji, 1961), Strongylocentrotus purpuratus (Holland and Nimitz, 1964), and Psammechinus miliaris (Buchanan, 1969). Less detailed studies have been made of the gut mucous cells in Diadema antillarism (Lewis, 1964) and Dendraster excentricus (Reisman, 1965). The species mentioned above represent but a few of the extant orders and families of echinoids. The lack of information about mucous cells in the class Echinoidea as a whole prompted the present investigation of the patterns of dis tribution and the histochemical properties of mucous cells in the guts of thirty seven species of echinoids, both regular and irregular. The same set of histo chemical methods was applied to each species in order to facilitate comparisons. The results have been interpreted phylogenetically in the context of a widely accepted scheme of macroevolution in the class Echinoidea (Durham and Melville, 1957). The echinoid taxonomy of Mortensen (1928, 1935, 1940, 1943a, 1943b, 1948, 1950, 1951) has been followed here because it is more suitable at the ordinal level than the newer echinoid taxonomy (summarized by McCormick and Moore, 1966) for condensing and summarizing the results of the present investi gation. During the course of the present study, some new facts about the gross anatomy of the echinoid siphon unexpectedly came to light and have necessarily been reported here. To date, the terminology for echinoid gut regions has not been standardized. Therefore, the terms used in this paper must be defined at the outset. In the