Stenopodidean shrimp of the genus Spongicola settle inside the sponge's hollow central cavity while small. The lattice openings admit larvae and juveniles but not full-grown adults, so the pair that remains inside is enclosed by the growing skeleton. They feed on particles carried through by the sponge's feeding current and, in turn, their movement and waste may benefit the host, though the balance of the relationship is not fully quantified.
The skeleton itself is the more studied feature. Its spicules are silica laid down in concentric layers with thin organic interlayers, and the whole tube uses a square lattice reinforced by diagonal struts, a geometry that engineers have analysed for its buckling resistance. Individual spicules also transmit light along their length in a manner comparable to optical fibre.
The wedding-gift tradition is real and gives the sponge the name of a lifelong bond. The claim sometimes attached to it, that the shrimp mate for life out of devotion, misstates a physical constraint as a behavioural one.