Aporocotyle simplex (Odhner, 1900)

Poddubnaya, Larisa G., Hemmingsen, Willy & MacKenzie, Ken, 2023, Digestive system of the marine blood fluke, Aporocotyle simplex (Odhner, 1900) (Digenea: Aporocotylidae) with consideration of the digenean digestive morphology, Zoologischer Anzeiger 305, pp. 11-22 : 12

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 ).

Figures

Fig. 1. Anterior foregut of Aporocotyle simplex (A) SEM view of anterior body region, note mouth opening (B, C) LM view of mouth opening, anterior and posterior esophagus, two anterior. and two posterior caeca and caecum bifurcation, note compact cell mass around esophageal portion (D, G) TEM view of anterior foregut portion showing mouth cavity, behind which there is a foregut portion with developed circular and radial muscles and the following anterior esophageal portion, note longitudinal muscle fibres surrounded anterior esophagus (E) Continuation of syncytial tegumental lining of the body into mouth cavity and anterior foregut, note sensory ending around mouth cavity and surface knob-like outgrowths (F) Anterior foregut side showing lateral fold and bunds of circular and radial muscles surrounding foregut syncytial cytoplasm, note well developed nerve plexus (H) Portion of body tegumental cytoplasm, note dense tegumental bodies within cytoplasm and knob-like outgrowths on the surface (I) Anterior foregut syncytial cytoplasm surrounded by circular and radial muscles. Abbreviations: ac, anterior caecum; aes, anterior esophagus; bl, basal lamina; cb, caecum bifurcation; cm, circular muscles; db, dense tegumental bodies; dtc, distal tegumental cytoplasm of the body; elm, esophageal longitudinal muscle fibres; em, extracellular matrix; fsc, foregut syncytial cytoplasm; hd, hemidesmosomes; lf, lateral fold; ko, knob-like outgrowths; maf, muscular portion of anterior foregut; mo, mouth opening; nf, nerve fibers; pc, posterior caecum; pes, posterior esophagus; rm, radial muscles; se, sensory ending; sm, surrounding cell masses; vi, vesicular inclusions. Scale bars: A = 50 μm; B = 200 μm; С = 100 μm; D = 5 μm; E, H, I = 1 μm; F, G = 2 μm.