Morphology and ultrastructure of the midgut in Piscicola geometra (Annelida, Hirudinea)

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

Ultrastructural changes in the midgut epithelium of Hypsibius dujardini (Doyère, 1840) (Tardigrada, Eutardigrada, Hypsibiidae) in relation to oogenesis

Hyra, Marta, Poprawa, Izabela, Włodarczyk, Agnieszka, Student, Sebastian, Sonakowska, Lidia, Kszuk-Jendrysik, Michalina, Rost-Roszkowska, Magdalena Maria (2016): Ultrastructural changes in the midgut epithelium of Hypsibius dujardini (Doyère, 1840) (Tardigrada, Eutardigrada, Hypsibiidae) in relation to oogenesis. Zoological Journal of the Linnean Society 178 (4): 897-906, DOI: 10.1111/zoj.12467, URL: http://dx.doi.org/10.1111/zoj.1246

Structure and Ultrastructure of the Endodermal Region of the Alimentary Tract in the Freshwater Shrimp <i>Neocaridina heteropoda</i> (Crustacea, Malacostraca)

<div><p>The freshwater shrimp <i>Neocaridina heteropoda</i> (Crustacea, Malacostraca, Decapoda) originates from Asia and is one of the species that is widely available all over the world because it is the most popular shrimp that is bred in aquaria. The structure and the ultrastructure of the midgut have been described using X-ray microtomography, transmission electron microscopy, light and fluorescence microscopes. The endodermal region of the alimentary system in <i>N</i>. <i>heteropoda</i> consists of an intestine and a hepatopancreas. No differences were observed in the structure and ultrastructure of males and females of the shrimp that were examined. The intestine is a tube-shaped organ and the hepatopancreas is composed of two large diverticles that are divided into the blind-end tubules. Hepatopancreatic tubules have three distinct zones – proximal, medial and distal. Among the epithelial cells of the intestine, two types of cells were distinguished – D and E-cells, while three types of cells were observed in the epithelium of the hepatopancreas – F, B and E-cells. Our studies showed that the regionalization in the activity of cells occurs along the length of the hepatopancreatic tubules. The role and ultrastructure of all types of epithelial cells are discussed, with the special emphasis on the function of the E-cells, which are the midgut regenerative cells. Additionally, we present the first report on the existence of an intercellular junction that is connected with the E-cells of Crustacea.</p></div

Secretion in the midgut epithelium.

<p>(A-B) Apocrine secretion in the intestine. Digestive cells (dc) with distinct evaginations of the apical membrane (arrows). (A) TEM. Bar = 1.7 µm. (B) TEM. Bar = 1.3 µm. (C) Microapocrine secretion: small bulges of microvilli (arrows) of the digestive cells (dc). TEM. Bar = 0.33 µm. Autophagosome (au), midgut lumen (l), microvilli (mv), nucleus (n), cortical layer of the apical cytoplasm (star), smooth septate junction (arrowhead).</p

The scanning parameters used during the tests using X-ray microtomography.

<p>The scanning parameters used during the tests using X-ray microtomography.</p

Changes in the fibrillar (fc) and storage (sc) cells according to their distance from the differentiation region of the tubule in <i>N</i>. <i>heteropoda</i>.

<p>TEM. (A) Bar = 1.7 µm. (B) Bar = 1.14 µm. (C) Bar = 1 µm. (D) Bar = 5.4 µm. (E) Bar = 6.5 µm. (F) Bar = 1.44 µm. (G) Bar = 1.32 µm. Hepatopancreatic lumen (l), microvilli (mv), basal lamina (bl), nucleus (n), reserve material (rm), vacuole (v), mitochondria (m), cisterns of the rough endoplasmic reticulum (RER), Golgi complexes (d), residual bodies (rb).</p

Differentiation region of hepatopancreatic tubules in <i>N</i>. <i>heteropoda</i>.

<p>(A) Cross section through the differentiation region. Light microscopy. Bar = 26 µm. (B) Longitudinal section through the differentiating region of tubule. TEM. Bar = 2.2 µm. (C) Cytoplasm of undifferentiated cells. TEM. Bar = 1.7 µm. (D) A higher magnification of (B). Apical membrane without any folds or microvilli (arrowhead) and distinct smooth septate junctions (arrows) between adjacent cells. TEM. Bar = 0.9 µm. (E) Cytoplasm rich in organelles. Gap junctions (arrows) between adjacent cells. TEM. Bar = 0.7 µm. (F) Sporadic regenerative cells (rc) with cytoplasm that was poor in organelles. TEM. Bar = 1 µm. Undifferentiated cells (uc), hepatopancreatic lumen (l), basal lamina (bl), nucleus (n), cisterns of the rough (RER) and smooth (SER) endoplasmic reticulum, mitochondria (m), Golgi complexes (d).</p

The epithelium of the intestine.

<p>(A) Two types of cells—digestive (dc) and regenerative cells (rc). Light microscopy. Bar = 21 µm. (B) Anterior fragment of the intestine with regenerative cells (rc) distributed among the basal regions of the digestive cells (dc). TEM. Bar = 2 µm. (C) The intestine epithelium (e) composed of only digestive cells (dc). TEM. Bar = 3 µm. (D) The apical cytoplasm of the digestive cells. TEM. Bar = 0.87 µm. (E) The apical cytoplasm in the digestive cells (dc) with actin filaments stained in red. Nuclei stained in blue. Fluorescent microscopy. Bar = 24.5 µm. (F-G) The perinuclear region of the cytoplasm. (F) TEM. Bar = 0.65 µm. (G) TEM. Bar = 0.75 µm. (H) Basal cytoplasm of the digestive cells with distinct folds of the basal membrane (arrows). TEM. Bar = 1.46 µm. (I) Gap junction (arrow). TEM. Bar = 0.93 µm. Intestine lumen (l), basal lamina (bl), visceral muscles (mc), nucleus (n), microvilli (mv), regions of the cytoplasm: 1—apical, 2—perinuclear, 3—basal, cisterns of the rough (RER) and smooth (SER) endoplasmic reticulum, autophagosomes (au), electron-dense vesicles (black arrows), electron-lucent vesicles (white arrows), smooth septate junction (arrowheads), mitochondria (m), Golgi complexes (d), septate junction (arrowheads).</p

Distal region of hepatopancreatic tubules in <i>N</i>. <i>heteropoda</i>.

<p>(A) Longitudinal section through the distal (arrows) and differentiating (arrowheads) regions of tubule with regenerative cells (rc). Light microscopy. Bar = 26 µm. (B) Cross section through the distal region with regenerative cells (rc). Light microscopy. Bar = 19 µm. (C) Regenerative cells (rc). TEM. Bar = 3.15 µm. (D) Regenerative cells (rc). TEM. Bar = 2.43 µm. (E) Septate junctions (arrow) between regenerative cells. TEM. Bar = 1 µm. Hepatopancreatic lumen (l), visceral muscles (mc), intestine (in), basal lamina (bl), nucleus (n), mitochondria (m), cisterns of the rough endoplasmic reticulum (RER).</p

The role and the localization of epithelial cells in endodermal region of the digestive system in Crustacea.

<p>The role and the localization of epithelial cells in endodermal region of the digestive system in Crustacea.</p