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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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Schematic organization (A) and habitus (B) of T. wilhelma aquiferous system.(A) Potential flow directions in the canal system are indicated with arrows (after [15]). A color gradient from light to dark blue in the canals indicates the allocation of the corresponding elements to the incurrent and excurrent system. Due to the presence of bypasses in the canal system flow directions cannot be assigned with certainty to all sections. This might even cause backflows from the excurrent to the incurrent system. Main features/structures of the canal system are labeled in the scanning electron micrograph (B) as well as in the schematic drawing (A).
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pone-0113153-g002: Schematic organization (A) and habitus (B) of T. wilhelma aquiferous system.(A) Potential flow directions in the canal system are indicated with arrows (after [15]). A color gradient from light to dark blue in the canals indicates the allocation of the corresponding elements to the incurrent and excurrent system. Due to the presence of bypasses in the canal system flow directions cannot be assigned with certainty to all sections. This might even cause backflows from the excurrent to the incurrent system. Main features/structures of the canal system are labeled in the scanning electron micrograph (B) as well as in the schematic drawing (A).

Mentions: The canal system architecture in T. wilhelma is of the leucon type with some striking manifestations of specific canal system elements. The incurrent canal system features voluminous cortical lacunar sub-dermal cavities. This cortical lacunar network is connected to an underlying network of sub-lacunar cavities located at the choanosome/cortex boundary. Both lacunar systems consist of an extensive network of anastomosing oval-shaped/flat canals. Branching off from the lacunar- and sub-lacunar cavities, high numbers of ramifying canals lead into the choanosome. Due to the roughly globular shape of the body, the canals of the incurrent and excurrent canal systems are significantly intertwined in the choanosome region. Within the excurrent canal system the atrium region stands out by virtue of its volume and can be characterized as a larger sized canal resembling a vestibule which opens directly into the outflow opening (oscule) (Figure 2). Depending on the state of morphological (re-)organization and environmental flow conditions, varying numbers of oscules are present, from one in the majority of cases to several in more rare cases.


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)

Schematic organization (A) and habitus (B) of T. wilhelma aquiferous system.(A) Potential flow directions in the canal system are indicated with arrows (after [15]). A color gradient from light to dark blue in the canals indicates the allocation of the corresponding elements to the incurrent and excurrent system. Due to the presence of bypasses in the canal system flow directions cannot be assigned with certainty to all sections. This might even cause backflows from the excurrent to the incurrent system. Main features/structures of the canal system are labeled in the scanning electron micrograph (B) as well as in the schematic drawing (A).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0113153-g002: Schematic organization (A) and habitus (B) of T. wilhelma aquiferous system.(A) Potential flow directions in the canal system are indicated with arrows (after [15]). A color gradient from light to dark blue in the canals indicates the allocation of the corresponding elements to the incurrent and excurrent system. Due to the presence of bypasses in the canal system flow directions cannot be assigned with certainty to all sections. This might even cause backflows from the excurrent to the incurrent system. Main features/structures of the canal system are labeled in the scanning electron micrograph (B) as well as in the schematic drawing (A).
Mentions: The canal system architecture in T. wilhelma is of the leucon type with some striking manifestations of specific canal system elements. The incurrent canal system features voluminous cortical lacunar sub-dermal cavities. This cortical lacunar network is connected to an underlying network of sub-lacunar cavities located at the choanosome/cortex boundary. Both lacunar systems consist of an extensive network of anastomosing oval-shaped/flat canals. Branching off from the lacunar- and sub-lacunar cavities, high numbers of ramifying canals lead into the choanosome. Due to the roughly globular shape of the body, the canals of the incurrent and excurrent canal systems are significantly intertwined in the choanosome region. Within the excurrent canal system the atrium region stands out by virtue of its volume and can be characterized as a larger sized canal resembling a vestibule which opens directly into the outflow opening (oscule) (Figure 2). Depending on the state of morphological (re-)organization and environmental flow conditions, varying numbers of oscules are present, from one in the majority of cases to several in more rare cases.

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