Models of flow through sponges must consider the sponge tissue

In their Article, Falcucci et al.1 examined the hydrodynamics of the deep-sea glass sponge Euplectella aspergillum using a model of just the skeleton of the sponge. The authors present simulations showing flow lines and vortices crossing the sponge skeleton from the upstream to the downstream side of the tube in crossflow and conclude that the skeletal motifs give rise to internal recirculation patterns favouring the sponge’s feeding and sexual reproduction. Unfortunately, in their
model, Falcucci et al.1 neglect the sponge’s tissue that, with its complex labyrinth of feeding canals, forms a complete barrier with low permeability over the sponge wall2–5 (Fig. 1). The implication of this omission is that the flow simulations are not informative regarding the actual flow through and around live E. aspergillum and thus speculations about the effect of the flow patterns they observed on sponge biology (feeding, reproduction and hydrodynamic stress) are unfounded.