Hydrodynamics of sponge pumps and evolution of the sponge body plan

Abstract

Sponges are suspension feeders that filter vast amounts of water. Pumping is carried out by flagellated chambers that are connected to an inhalant and exhalant canal system. In 'leucon' sponges with relatively high-pressure resistance due to a complex and narrow canal system, pumping and filtering are only possible owing to the presence of a gasket-like structure (forming a canopy above the collar filters). Here we combine numerical and experimental work, and demonstrate how sponges that lack such sealing elements are able to efficiently pump and force the flagella driven flow through their collar filter, thanks to the formation of a 'hydrodynamic gasket' above the collar. Our findings link the architecture of flagellated chambers to that of the canal system, and lend support to the current view that the sponge aquiferous system evolved from an open-type filtration system, and that the first metazoans were filter feeders.

Fine details of the choanocyte filter apparatus in asconoid calcareous sponges (Porifera: Calcarea) revealed by ruthenium red fixation

“…The "hydrodynamic gasket" ensures high effective particle capture, preventing them from bypassing the collars in the absence of a glycocalyx strainer. At the same time, the "hydrodynamic gasket" is inefficient in preventing re-filtering of water, and a large portion of water is recirculated inside the chamber (Asadzadeh et al, 2020). The study by Asadzadeh et al (2020) confirms that choanocyte chambers without physical sealing elements could be effective pumping units in open aquiferous systems.…”

“…It is generally accepted that these glycocalyx structures are required for pumping only in sponges with the leuconoid aquiferous system as they have an extended and elaborated system of canals, which generate substantial resistance for the water flow (Asadzadeh et al, 2019(Asadzadeh et al, , 2020. In the case of open-type aquiferous systems of asconoid and syconoid sponges (characterized by rather short canals and voluminous cavities lined by the choanocytes), it is assumed that glycocalyx structures are redundant as there is no need for high pressure differences to pump water (Asadzadeh et al, 2019(Asadzadeh et al, , 2020.…”

“…It is generally accepted that these glycocalyx structures are required for pumping only in sponges with the leuconoid aquiferous system as they have an extended and elaborated system of canals, which generate substantial resistance for the water flow (Asadzadeh et al, 2019(Asadzadeh et al, , 2020. In the case of open-type aquiferous systems of asconoid and syconoid sponges (characterized by rather short canals and voluminous cavities lined by the choanocytes), it is assumed that glycocalyx structures are redundant as there is no need for high pressure differences to pump water (Asadzadeh et al, 2019(Asadzadeh et al, , 2020. A recent study on another sponge with open-type aquiferous system, the syconoid S. coactum, combining computational modeling and experimental approach shows that at least this species can substitute a physical strainer made of glycocalyx by creating a "hydrodynamic gasket" above choanocytes' collars (Asadzadeh et al, 2020).…”

“…In the case of open-type aquiferous systems of asconoid and syconoid sponges (characterized by rather short canals and voluminous cavities lined by the choanocytes), it is assumed that glycocalyx structures are redundant as there is no need for high pressure differences to pump water (Asadzadeh et al, 2019(Asadzadeh et al, , 2020. A recent study on another sponge with open-type aquiferous system, the syconoid S. coactum, combining computational modeling and experimental approach shows that at least this species can substitute a physical strainer made of glycocalyx by creating a "hydrodynamic gasket" above choanocytes' collars (Asadzadeh et al, 2020). The "hydrodynamic gasket" is a stagnation zone created by two opposite flows: by the inhalant flow from an ostium and the backflow generated by pressure drop above the ostium.…”

“…In contrast, asconoid and syconoid sponges possess simpler aquiferous system organization with relatively short canal systems and numerous choanocytes lining large cavities (Leys and Hill, 2012;Ereskovsky and Lavrov, 2021). It is thought that they do not need high pressure difference to pump water through their aquiferous system and, consequently, do not have the low-and highpressure zones and corresponding structural features in their choanocyte cavities (Leys and Eerkes-Medrano, 2006;Pozdnyakov and Karpov, 2013;Asadzadeh et al, 2019Asadzadeh et al, , 2020.…”