Digestive system of the marine blood fluke, Aporocotyle simplex (Odhner, 1900) (Digenea: Aporocotylidae) with consideration of the digenean digestive morphology Author Poddubnaya, Larisa G. Author Hemmingsen, Willy Author MacKenzie, Ken text Zoologischer Anzeiger 2023 2023-07-31 305 11 22 http://dx.doi.org/10.1016/j.jcz.2023.05.003 journal article 281827 10.1016/j.jcz.2023.05.003 fef84de4-8e9b-4218-84b9-1c3a3c507240 1873-2674 10376067 3.1. The anterior foregut of A. simplex With SEM, the anterior extremity of the A. simplex body has an anterior depression opening into the mouth cavity ( Fig. 1A ). In LM Fig. 1B and C the long esophagus surrounded by the compact cellular masses, which extend up to the bifurcation of the H-shaped caecum, may be clearly seen, with shorter right and left anterior caeca and longer right and left posterior caeca, which end near the posterior extremity ( Fig. 1B ). In TEM longitudinal sections, the mouth cavity is funnelshaped ( Fig. 1D–F ), and the ciliated sensory endings are located around the mouth cavity ( Fig. 1E ). The syncytial lining of the anterior foregut is continuous with the distal syncytial tegumental cytoplasm of the body and both have similar cytoplasmic inclusions, electron-dense tegumental bodies and vesicular inclusions ( Fig. 1E and H ). The syncytial lining of the body and anterior foregut is surrounded by thin basal lamina and a thick extracellular basal matrix separates the syncytial cytoplasm from the underlying muscle fibres; their luminal surface bears irregular knob-like outgrowths ( Fig. 1E and H ). Behind the mouth cavity, the foregut syncytial lining (about 15–22 μm in the length) is surrounded by circular and radial muscle fibres ( Fig. 1D, F, G ). Directly beneath the extracellular matrix surrounding this foregut region (muscular anterior foregut), circular muscle fibres are arranged into 8–10 isolated bands on each canal side ( Fig. 1D–G ). Radial muscle fibres appear to run between the circular bands ( Fig. 1E, F, I ). These radial fibres represent the branchings of two powerful radial bands of antero-lateral orientation situated on both sides of this foregut region ( Fig. 1D F, G ). The distal margins of the radial muscles are attached by hemidesmosomes to the canal extracellular matrix ( Fig. 1I ). The muscle fibres of the anterior foregut are supplied with nerve fibres ( Fig. 1F ). Some deep lateral folds of the distal epithelial layer may be observed along the anterior foregut ( Fig. 1E, F, G ).