Figure 1.
Scheme of hydrodynamic conditions in different sections of the leuconoid canal system based on morphometric and anatomical data on the sponge canal system as well as on fundamental physical laws in hydrodynamics [3], [4], [6], [9]–[11], [46].
(A) Structural representation of the main canal system elements in the direction of flow. (B) Schematic diagram of the change of available total cross sectional area along the flow path. (C) Schematic diagram of flow velocities in the canal system. (D) Schematic diagram of the change of pressure drop along the flow path.
Figure 2.
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).
Figure 3.
Scanning electron micrograph of an ostia pore field (A), a single ostium (B) and details of ostia in an ostia pore field (C).
Figure 4.
Scanning electron micrograph of cellular structures in the choanocyte chamber.
(A) Overview of a choanocyte chamber connected to an incurrent- and excurrent canal with the relevant cellular prosopylar and apopylar elements and the location of the new cell type: reticuloapopylocyte. (B) Circular arrangement of apopylar cells and the position adjacent to reticuloapopylocyte. Hydrodynamic sealing of apopylar velum and microvilli collar. (C) Arrangement of cilium bearing apopylar cells, choanocytes and reticuloapopylocytes in the choanocytic apopyle. (D) Detailed view of an apopylar cell with its cilium directing into the flow at the apopyle. (E) Detailed view of the apopylar velum and microvilli collar contact side which results in a hydrodynamic sealing. (F) Overview of prosopylar openings in the incurrent canal system. (G) Pore cell forming a prosopylar opening. In the background microvilli collars of choanocytes are visible.
Figure 5.
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.
Figure 6.
Scanning electron micrographs of pinacocytes.
(A) Highly ordered apendopinacocytes in the atrium region. (B) Monociliated apendopinacocytes in the excurrent canal system. (C) Detailed view of a monociliated apendopinacocyte. (D) Prosendopinacocytes lining the walls of the incurrent canal system. (E) Detail of the cilium of an apendopinacocyte. (F) Cross section of an exopinacocyte lining the outer surface of T. wilhelma. Note the T-shaped umbrella like cross sectional morphology with the cell body of the pinacocyte sunk into the extra cellular matrix.
Figure 7.
Schematic drawing of a choanocyte chamber with indicated flow directions and hydrodynamically pivotal sites (stars): 1. prosopyle, 2. microvilli collar, 3. contact side between apopylar velum of monociliated apopylar cells and microvilli collar of choanocytes at the apopylar opening, 4. reticuloapopylocyte.