The periesophageal celom of the articulate brachiopod Hemithyris psittacea (Rhynchonelliformea, Brachiopoda)

Abstract

The celomic system of the articulate brachiopod Hemithyris psittacea is composed of the perivisceral cavity, the canal system of the lophophore, and the periesophageal celom. We study the microscopic anatomy and ultrastructure of the periesophageal celom using scanning and transmission electron microscopy. The periesophageal celom surrounds the esophagus, is isolated from the perivisceral cavity, and is divided by septa. The lining of the periesophageal celom includes two types of cells, epithelial cells and myoepithelial cells, both are monociliary. Some epithelial cells have long processes extending along the basal lamina, suggesting that these cells might function as podocytes. The myoepithelial cells have basal myofilaments and may be overlapped by the apical processes of the adjacent epithelial cells. The periesophageal celom forms protrusions that penetrate the extracellular matrix (ECM) of the body wall above the mouth and the ECM that surrounds the esophagus. The canals of the esophageal ECM form a complicated system. The celomic lining of the external circumferential canals consists of the epithelial cells and the podocyte-like cells. The deepest canals lack a lumen; they are filled with the muscle cells surrounded by basal lamina. These branched canals might perform dual functions. First, they increase the surface area and might therefore facilitate ultrafiltration through the podocyte-like cells. Second, the deepest canals form the thickened muscle wall of the esophagus and could be necessary for antiperistalsis of the gut.

Ultrastructure of the coelom in the brachiopodLingula anatina

“…Most adult brachiopods have two coelomic compartments: the lophophore coelom and the trunk coelom (Hancock, 1859; Lüter, 2007). At the same time, additional cavities in the brachiopod lophophore are described (Blochmann, 1892; Kuzmina & Malakhov, ; Kuzmina, Malakhov, & Temereva, ; Pross, ). The presence of the true coelom in the brachial fold of Lingula anatina was recently demonstrated (Temereva et al, ).…”

“…In brachiopods, only the bipartite type of coelomic system was known until recently (Lüter, ). Some observations indicate, however, the presence of additional cavities in the brachiopod lophophore, but the nature of these cavities has not been clearly established (Kuzmina & Malakhov, ; Pross, ). The preoral coelom was recently described in the inarticulate brachiopod Lingula anatina (Temereva, Gebruk, & Malakhov, ).…”

Demonstration of the preoral coelom in the brachiopod Lingula anatina with consideration of its phylogenetic significance

“…On the other hand, in literature there are some data about presence of addition cavities in the brachiopod lophophore (Blochmann, 1892Blochmann, 1892Pross, 1980Kuzmina et al, 2006;Kuzmina and Malakhov, 2011). In some brachiopods, these cavities penetrate the connective tissue around Abbreviations: am, apical microvilli; bl, basal lamina; bp, basal projection; c, cilium; cc1, cells of lining of epistomal cavity; ct, connective tissue; d, desmosoma; ec, epistomal cavity; food groove; g, granule; hd, hemidesmosoma; lc, large canal of the lophophore; m, mitochondrion; mc, muscle cells; n, nucleus; sc, small canal of the lophophore; t, tentacle; tlj, tight junction.…”

“…In some brachiopods, these cavities penetrate the connective tissue around Abbreviations: am, apical microvilli; bl, basal lamina; bp, basal projection; c, cilium; cc1, cells of lining of epistomal cavity; ct, connective tissue; d, desmosoma; ec, epistomal cavity; food groove; g, granule; hd, hemidesmosoma; lc, large canal of the lophophore; m, mitochondrion; mc, muscle cells; n, nucleus; sc, small canal of the lophophore; t, tentacle; tlj, tight junction. the esophagus (Blochmann, 1892; Malakhov, 2011 Kuzmina andMalakhov, 2011), but in other brachiopods, these cavities are located at the base of the prosome-the brachial fold (Pross, 1980). Although the latter paper considered whether the brachiopod epistomal cavity is homologous with the phoronid protocoel, it did not clearly establish the nature of the epistomal cavity.…”

“…According to previous reports, they have only two coeloms: trunk and lophophoral (Williams et al, 2007). At the same time, some data indicate the presence of additional cavities in the brachiopod lophophore, but the nature of these cavities has not been clearly established (Pross, 1980;Kuzmina and Malakhov, 2011).…”