Ultrastructure of the foregut and associated glands in the lung fluke,Paragonimus miyazakii (Digenea: Troglotrematidae), with particular reference to their functional roles

Abstract

The foregut and associated glands of a digenetic trematode, Paragonimus miyazakii, were examined in the forebody by transmission and scanning electron microscopy as well as by light microscopy, and their functional roles were discussed. The foregut is lined with a general tegument without spines and sensory receptors throughout its length, although it consists of the mouth, pharynx, and esophagus. This foregut tegument is regionally and intraregionally modified in appearance, suggesting the performance of auxiliary functions in digestion. This appearance is characterized by long, frequent cytoplasmic extensions of the apical tegument around the middle portion of the mouth and the anterior esophagus. Electron‐dense granules and multimembranous and multilamellar bodies are developed in the tegument to various degrees, and elaborately in the apical layer of the prepharynx. A single type of unicellular gland is embedded in the antero‐middle part of the worm in small groups. The gland cells synthesize clear secretory granules as a chief product, each granule with a pleomorphic, dense, core‐like inclusion. Mature granules are elliptical in shape, approximately 500 nm in diameter, and are subsequently discharged into the prepharyngeal foregut lumen after passing through the elongated cytoplasm of the gland cell. In the prepharynx and pharynx, host blood cells are apparently processed for digestion. In the wide lumen of the esophagus, foodstuff could undergo sufficient digestion prior to absorption by the cecal epithelium. J. Morphol. 237:43–52, 1998. © 1998 Wiley‐Liss, Inc.

Ultrastructure of the digestive tract of Gyliauchen nahaensis (Platyhelminthes, Digenea), an inhabitant of the hindgut of herbivorous fishes

“…This form of polarization is observed in other neodermatans, particularly the cestodes (Jones, 1993(Jones, , 1998. Other authors have observed forms of regional specialization in the foregut of other digeneans (Halton and McCrae, 1985;McMichael-Phillips et al, 1994a,b;Orido et al, 1998), but rarely do the regions differ as markedly . Gyliauchen nahaensis, middle esophagus, TEM.…”

“…In some digeneans the foregut can be complex (Halton and McCrae, 1985;McMichael-Phillips et al, 1994a,b;Orido et al, 1998). The foregut functions in food assimilation and initiates digestion, the latter function arising from secreted components derived from the tegument foregut (Dunn et al, 1987;Mattison et al, 1992) or from distinct unicellular glands that open directly into the esophageal lumen (Orido et al, 1998). The lining and insunken cell bodies of the anterior and middle esophagus of Gyliauchen nahaensis are rich in spherical vesicles resembling the T3 bodies described for other digeneans (Mattison et al, 1992).…”

Ultrastructure of the digestive tract ofGyliauchen nahaensis (Platyhelminthes, Digenea), an inhabitant of the hindgut of herbivorous fishes

“…The foregut functions in food assimilation and initiates digestion, the latter function arising from secreted components derived from the tegument foregut (Dunn et al, 1987;Mattison et al, 1992) or from distinct unicellular glands that open directly into the esophageal lumen (Orido et al, 1998). The lining and insunken cell bodies of the anterior and middle esophagus of Gyliauchen nahaensis are rich in spherical vesicles resembling the T3 bodies described for other digeneans (Mattison et al, 1992).…”

“…In some digeneans the foregut can be complex (Halton and McCrae, 1985;McMichael-Phillips et al, 1994a,b;Orido et al, 1998). The foregut functions in food assimilation and initiates digestion, the latter function arising from secreted components derived from the tegument foregut (Dunn et al, 1987;Mattison et al, 1992) or from distinct unicellular glands that open directly into the esophageal lumen (Orido et al, 1998).…”