Photo: Bridget Bradshaw, Heron Island, 2013.

Nervous and Sensory System

All bryozoans posses a central ganglionic mass located on the dorsal side of their lophophore.  From the ganglion runs a set of nerves—one per tentacle—forming a nerve ring around the pharynx, as well as a nerve net around the body wall.  While there are no specific sensory organs, though there are individual sensory cilia on the tentacles used to detect particles worthy of proactive consumption (Ruppert et al. 2004)).  While not observed directly in R. graeffei, in some genera the individual zooids of a colony are connected by nerves that run through the interzooidal pores (Ryland 1970).  Understandably, the coordination of feeding activity and response to predation (or other disturbance) within the colony would be advantageous in order to more efficiently feed or retract protruding lophophores at the first touch of abrowsing nudibranch.