Journal of Phylogenetics & Evolutionary Biology

Histological and Scanning Electron Microscopic Examination of the Digestive Tract in Whitespotted Conger, Conger Myriaster (Anguilliformes)

Abstract

Shunpei Takiue and Hideo Akiyoshi

The morphology of the digestive tract of Whitespotted conger, Conger myriaster (Elopomorpha: Anguilliformes) was examined by light and scanning electron microscopy. The digestive tracts consist of esophagus, stomach, and intestine; no pyloric caeca were observed. The stomach was divided into cardiac, body, terminal and pyloric region. The esophagus was composed of two layers of striated muscularis; inner longitudinal layer and outer circular layer. The former was extended to the body region of the stomach. In contrast, the latter was terminated to the esophagus, and became coincident to the boundary of the outer longitudinal layer consisting of smooth muscle in the cardiac region of the stomach. The terminal region of the stomach was characterized by the thick longitudinal muscularis and subserosa, and the gastric glands were absent. Ciliated cells were distributed in the intestinal wall. The digestive tract secreted both acidic and neutral mucus throughout all regions. We found that the terminal region of the stomach is characteristic of Anguilliformes. On the other hand, the striated muscle within the body region of the stomach was unique among the Anguilliformes. These differences in stomach suggested the possible existence of morphological differences that originate from phylogenetic position among the orders in Elopomorpha.