Another non-obligate symbiosis is known from encrusting bryozoans and hermit crabs that live in a close relationship. The bryozoan colony (Acanthodesia commensale) develops a cirumrotatory growth and offers the crab (Pseudopagurus granulimanus) a helicospiral-tubular extension of its living chamber that initially was situated within a gastropod shell.

What type of symbiosis seen between bryozoans and hermit crabs?