Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007, Katowice, Poland.
Protoplasma. 2012 Oct;249(4):1037-47. doi: 10.1007/s00709-011-0337-7. Epub 2011 Oct 21.
This paper presents information on the organization of the midgut and its epithelium ultrastructure in juvenile and adult specimens of Piscicola geometra (Annelida, Hirudinea), a species which is a widespread ectoparasite found on the body and gills and in the mouth of many types of fish. The analysis of juvenile nonfeeding specimens helped in the explanation of all alterations in the midgut epithelium which are connected with digestion. The endodermal portion (midgut) of the digestive system is composed of four regions: the esophagus, the crop, the posterior crop caecum, and the intestine. Their epithelia are formed by flat, cuboidal, or columnar digestive cells; however, single small cells which do not contact the midgut lumen were also observed. The ultrastructure of all of the regions of the midgut are described and discussed with a special emphasis on their functions in the digestion of blood. In P. geometra, the part of the midgut that is devoid of microvilli is responsible for the accumulation of blood, while the epithelium of the remaining part of the midgut, which has a distinct regionalization in the distribution of organelles, plays a role in its absorption and secretion. Glycogen granules in the intestinal epithelium indicate its role in the accumulation of sugar. The comparison of the ultrastructure of midgut epithelium in juvenile and adult specimens suggests that electron-dense granules observed in the apical cytoplasm of digestive cells take part in enzyme accumulation. Numerous microorganisms were observed in the mycetome, which is composed of two large oval diverticles that connect with the esophagus via thin ducts. Similar microorganisms also occurred in the cytoplasm of the epithelium in the esophagus, the crop, the intestine, and in their lumen. Microorganisms were observed both in fed adult and unfed juvenile specimens of P. geometra, which strongly suggests that vertical transmission occurs from parent to offspring.
本文介绍了广泛分布于多种鱼类体表、鳃部和口腔的寄生性蛭类鱼蛭属（环节动物门，蛭纲）幼体和成体的中肠组织和上皮超微结构。对非摄食幼体的分析有助于解释与消化有关的中肠上皮的所有变化。消化系统的内胚层部分（中肠）由四个区域组成：食管、嗉囊、后嗉囊盲囊和肠。它们的上皮由扁平的、立方的或柱状的消化细胞组成；然而，也观察到了不与中肠腔接触的单个小细胞。描述并讨论了所有中肠区域的超微结构，并特别强调了它们在血液消化中的功能。在鱼蛭属中，无微绒毛的中肠部分负责血液的积累，而其余部分的中肠上皮具有明显的细胞器分布区域化，在其吸收和分泌中起作用。肠上皮中的糖原颗粒表明其在糖积累中的作用。幼体和成体鱼蛭中肠上皮超微结构的比较表明，观察到的顶细胞质中电子致密颗粒参与了酶的积累。在由两个大的椭圆形憩室组成的真菌体中观察到大量微生物，它们通过细管与食管相连。类似的微生物也存在于食管、嗉囊、肠及其腔中的上皮细胞质中。在摄食的成年和未摄食的幼体鱼蛭中都观察到了微生物，这强烈表明垂直传播是从亲代到子代的。
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