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Abstract
AbstractThe ultrastructure of the gut regions of the marine filter‐feeder Phoronis vancouverensis was correlated with enzyme activity as revealed histochemically. The oesophagus, proventriculus, and stomach epithlia showed intense esterase and acid and alkaline phosphatase activity. The staining reaction was confined primarily to small globules in the apical cytoplasm of the epithlial cells. Electron micrographs of the same regions showed a high incidence of zymogenlike granules, with a corresponding abundance of ribosomes and of rough endoplasmic reticulum. Also, the proventricular and to a lesser extent the stomach epithelia were found to contain a large number of lipid bodies. This was confirmed with positive Sudan IV staining for fats.The intestinal region of the gut was found devoid of esterase and phosphatase activity. The epithelial surface in this region was found elaborated into microvilli. The entire gut is ci iated. A new paired‐cilium apparatus is described in this phylum.From these findings Phoronis vancouverensis is concluded to be suitably adapted to its continuous filter‐feeding existence, with the anterior gut epithelia synthesizing hydrolytic enzymes for release into the lumina of the proventriculus and stomach. Subsequently, in the hindgut the products of initial extra‐cellular digestion are absorbed via the microvilli and treated intracellularly within the intestinal epithelium. The proventriculus is further thought to function in lipid absorption and storage. The presence of chromaffin‐like granules observed in some proventricular and intestinal epithelial cells suggests that digestion in this phylum may in part be under neurosecretory control.
Published Version
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