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A new flow-regulating cell type in the Demosponge Tethya wilhelma - functional cellular anatomy of a leuconoid canal system.

Hammel JU, Nickel M - PLoS ONE (2014)

Bottom Line: We found a hitherto undescribed cell type, the reticuloapopylocyte, which is involved in flow regulation in the choanocyte chambers.These states permit a gradual regulation of the total apopylar opening area.Our study provides insights into the local and global flow conditions in the sponge canal system and thus enhances current understanding of related physiological processes.

View Article: PubMed Central - PubMed

Affiliation: Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Erbertstr. 1, 07743, Jena, Germany.

ABSTRACT
Demosponges possess a leucon-type canal system which is characterized by a highly complex network of canal segments and choanocyte chambers. As sponges are sessile filter feeders, their aquiferous system plays an essential role in various fundamental physiological processes. Due to the morphological and architectural complexity of the canal system and the strong interdependence between flow conditions and anatomy, our understanding of fluid dynamics throughout leuconoid systems is patchy. This paper provides comprehensive morphometric data on the general architecture of the canal system, flow measurements and detailed cellular anatomical information to help fill in the gaps. We focus on the functional cellular anatomy of the aquiferous system and discuss all relevant cell types in the context of hydrodynamic and evolutionary constraints. Our analysis is based on the canal system of the tropical demosponge Tethya wilhelma, which we studied using scanning electron microscopy. We found a hitherto undescribed cell type, the reticuloapopylocyte, which is involved in flow regulation in the choanocyte chambers. It has a highly fenestrated, grid-like morphology and covers the apopylar opening. The minute opening of the reticuloapopylocyte occurs in an opened, intermediate and closed state. These states permit a gradual regulation of the total apopylar opening area. In this paper the three states are included in a theoretical study into flow conditions which aims to draw a link between functional cellular anatomy, the hydrodynamic situation and the regular body contractions seen in T. wilhelma. This provides a basis for new hypotheses regarding the function of bypass elements and the role of hydrostatic pressure in body contractions. Our study provides insights into the local and global flow conditions in the sponge canal system and thus enhances current understanding of related physiological processes.

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Scanning electron micrographs of reticuloapopylocytes.(A) View on reticuloapopylocytes from the excurrent canal with adjacent endopinacocytes and most of the pores open. (B) View on reticuloapopylocytes from the excurrent canal with one cell having most of the pores closed. (c) Overview of the position of reticuloapopylocytes in the apopyle (cross section through a choanocyte chamber). (D) Detailed view on pores of reticuloapopylocytes in an open and closed state. (E) Color coded and labeled ferret pore diameter of reticuloapopylocyte. (F) Distribution of ferret pore diameters in reticuloapopylocytes.
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pone-0113153-g005: Scanning electron micrographs of reticuloapopylocytes.(A) View on reticuloapopylocytes from the excurrent canal with adjacent endopinacocytes and most of the pores open. (B) View on reticuloapopylocytes from the excurrent canal with one cell having most of the pores closed. (c) Overview of the position of reticuloapopylocytes in the apopyle (cross section through a choanocyte chamber). (D) Detailed view on pores of reticuloapopylocytes in an open and closed state. (E) Color coded and labeled ferret pore diameter of reticuloapopylocyte. (F) Distribution of ferret pore diameters in reticuloapopylocytes.

Mentions: The choanocytic apopyle is formed by apopylar cells (Figure 4B–D), two to three of which (depending on the size of the choanocyte chamber) form a ring-like structure (Figure 4B). Each apopylar cell bears a single cilium 3.9 µm in length (Figure 4D). In a cross-sectional view the ring formed by apopylar cells around the apopylar opening displays a characteristic double cone shape [26] (Figure 4C). On the choanocytic face the apopylar cells come into contact with choanocytes by way of a thin velum which forms the edge of the inner part of the ring/pore structure. This velum comes into direct contact with the choanocyte microvilli collar. The single cilium of the apopylar cells projects into the apopylar opening (Figure 4B–D). Facing the apopyle the cells connect to an apopylar pore-forming apendopinacocyte, which in turn touches a hitherto undescribed cell type spanning the apopylar opening (Figure 4B, Figure 5).


A new flow-regulating cell type in the Demosponge Tethya wilhelma - functional cellular anatomy of a leuconoid canal system.

Hammel JU, Nickel M - PLoS ONE (2014)

Scanning electron micrographs of reticuloapopylocytes.(A) View on reticuloapopylocytes from the excurrent canal with adjacent endopinacocytes and most of the pores open. (B) View on reticuloapopylocytes from the excurrent canal with one cell having most of the pores closed. (c) Overview of the position of reticuloapopylocytes in the apopyle (cross section through a choanocyte chamber). (D) Detailed view on pores of reticuloapopylocytes in an open and closed state. (E) Color coded and labeled ferret pore diameter of reticuloapopylocyte. (F) Distribution of ferret pore diameters in reticuloapopylocytes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4237394&req=5

pone-0113153-g005: Scanning electron micrographs of reticuloapopylocytes.(A) View on reticuloapopylocytes from the excurrent canal with adjacent endopinacocytes and most of the pores open. (B) View on reticuloapopylocytes from the excurrent canal with one cell having most of the pores closed. (c) Overview of the position of reticuloapopylocytes in the apopyle (cross section through a choanocyte chamber). (D) Detailed view on pores of reticuloapopylocytes in an open and closed state. (E) Color coded and labeled ferret pore diameter of reticuloapopylocyte. (F) Distribution of ferret pore diameters in reticuloapopylocytes.
Mentions: The choanocytic apopyle is formed by apopylar cells (Figure 4B–D), two to three of which (depending on the size of the choanocyte chamber) form a ring-like structure (Figure 4B). Each apopylar cell bears a single cilium 3.9 µm in length (Figure 4D). In a cross-sectional view the ring formed by apopylar cells around the apopylar opening displays a characteristic double cone shape [26] (Figure 4C). On the choanocytic face the apopylar cells come into contact with choanocytes by way of a thin velum which forms the edge of the inner part of the ring/pore structure. This velum comes into direct contact with the choanocyte microvilli collar. The single cilium of the apopylar cells projects into the apopylar opening (Figure 4B–D). Facing the apopyle the cells connect to an apopylar pore-forming apendopinacocyte, which in turn touches a hitherto undescribed cell type spanning the apopylar opening (Figure 4B, Figure 5).

Bottom Line: We found a hitherto undescribed cell type, the reticuloapopylocyte, which is involved in flow regulation in the choanocyte chambers.These states permit a gradual regulation of the total apopylar opening area.Our study provides insights into the local and global flow conditions in the sponge canal system and thus enhances current understanding of related physiological processes.

View Article: PubMed Central - PubMed

Affiliation: Institut für Spezielle Zoologie und Evolutionsbiologie mit Phyletischem Museum, Friedrich-Schiller-Universität Jena, Erbertstr. 1, 07743, Jena, Germany.

ABSTRACT
Demosponges possess a leucon-type canal system which is characterized by a highly complex network of canal segments and choanocyte chambers. As sponges are sessile filter feeders, their aquiferous system plays an essential role in various fundamental physiological processes. Due to the morphological and architectural complexity of the canal system and the strong interdependence between flow conditions and anatomy, our understanding of fluid dynamics throughout leuconoid systems is patchy. This paper provides comprehensive morphometric data on the general architecture of the canal system, flow measurements and detailed cellular anatomical information to help fill in the gaps. We focus on the functional cellular anatomy of the aquiferous system and discuss all relevant cell types in the context of hydrodynamic and evolutionary constraints. Our analysis is based on the canal system of the tropical demosponge Tethya wilhelma, which we studied using scanning electron microscopy. We found a hitherto undescribed cell type, the reticuloapopylocyte, which is involved in flow regulation in the choanocyte chambers. It has a highly fenestrated, grid-like morphology and covers the apopylar opening. The minute opening of the reticuloapopylocyte occurs in an opened, intermediate and closed state. These states permit a gradual regulation of the total apopylar opening area. In this paper the three states are included in a theoretical study into flow conditions which aims to draw a link between functional cellular anatomy, the hydrodynamic situation and the regular body contractions seen in T. wilhelma. This provides a basis for new hypotheses regarding the function of bypass elements and the role of hydrostatic pressure in body contractions. Our study provides insights into the local and global flow conditions in the sponge canal system and thus enhances current understanding of related physiological processes.

Show MeSH
Related in: MedlinePlus