Contraction-Expansion and the Effects on the Aquiferous System in the Demosponge Halichondria panicea

Abstract

Contractile behavior is common among sponges despite their lack of nerves and muscles. As sessile filter-feeders, sponges rely on water with suspended food particles being pumped through their aquiferous system. During contractions, however, the water flow is being reduced and eventually shut down. Yet, purpose and underlying pathways of contractile behavior have remained largely unclear. Here, we document the external and internal morphology of contracted and expanded single-osculum explants of the demosponge Halichondria panicea. We show that contraction-expansion dynamics can occur spontaneously (in untreated explants) and can be induced by exposure to chemical messengers such as γ-aminobutyric acid (GABA, 1 mM) and L-glutamate (L-Glu, 1 mM), or to inedible ink particles (4 mg L −1). The neurotransmitter GABA triggered similar contraction-expansion dynamics in H. panicea as observed in untreated explants. The effects of GABA-induced contraction-expansion events on the aquiferous system were investigated using scanning electron microscopy (SEM) on cryofractured explants. Our findings suggest that contraction-expansion affects the entire aquiferous system of H. panicea, including osculum, ostia, in-and excurrent canals and apopyles.

Reafference and the origin of the self in early nervous system evolution

“…Some sponges can also actively change their body shape by contraction and extension [ 51 , 110 – 112 ]. A well-known case is the ‘sneeze’ of the freshwater sponge E. muelleri .…”

“…It remains unclear whether these shape changes induce any stretch-dependent monitoring of body shape. Some sponges can also actively change their body shape by contraction and extension [51,[110][111][112]. A well-known case is the 'sneeze' of the freshwater sponge E. muelleri.…”

Differences in the Structural Components Influence the Pumping Capacity of Marine Sponges

“…The internal and external surfaces of sponges are covered by pinacoderm which is made of flat cells called pinacocytes. Sponges are known to actively close and open the oscula and ostia present on the pinacoderm, thus effectively regulating the water flow (Nickel, 2004(Nickel, , 2010Ellwanger and Nickel, 2006;Elliott and Leys, 2007;Ludeman et al, 2014;Goldstein et al, 2020). Some species show a flow-regulating cell type "reticuloapopylocyte" at the apopylar opening of the CC, suggesting a possibility of flow control mechanism at the level of individual CC and their connecting canals (Hammel and Nickel, 2014;Ludeman et al, 2016).…”

“…Some species show a flow-regulating cell type "reticuloapopylocyte" at the apopylar opening of the CC, suggesting a possibility of flow control mechanism at the level of individual CC and their connecting canals (Hammel and Nickel, 2014;Ludeman et al, 2016). Several sponge species are capable of coordinated contractions (Nickel, 2010), and pinacoderm acts as a major conductive pathway during contraction processes which lead to the collapse of the internal void spaces in the form of in and excurrent canals and the subdermal cavities (Hammel et al, 2012;Goldstein et al, 2020). Thus, sponges control the surface pores, as well as the internal porosity, and effectively manage the volume of water pumped and filtered.…”

Reafference and the origin of the self in early nervous system evolution

“…It remains unclear whether these shape-changes induce any stretchdependent monitoring of body shape. Some sponges can also actively change their body shape by contraction and extension [110] [111][48] [112]. A well-known case is the 'sneeze' of the freshwater sponge E. muelleri.…”