Sits on the hydroids it eats, and is shaped enough like them to be swum past.
A dendronotid to about 6 cm, cream to pale orange, the body overlaid with a network of orange-brown to red lines and carrying several pairs of branched processes down the back. At the base of each process is a cluster of finely divided gills arranged in a radiating rosette, which is the feature the name refers to. The rhinophores rise from tall sheaths that are themselves branched at the rim. Against Bornella anguilla, the other one regularly seen here: at the same length anguilla is narrower and more eel-like, with a finer and more even network of lines and smaller gill clusters at the bases of the processes.
Feeds on hydroids and is found on them, most often at night, occasionally in daylight on the same colonies. The whole animal is more three-dimensional than a dorid and at rest on a hydroid it reads as part of the colony, so it is usually found by working along hydroid growth on rubble, wreckage and jetty pilings rather than by scanning open ground. Recorded from about 3 to 25 m.
The genus swims by flexing the whole body from side to side, and this species will do it if it is knocked off the colony. That is worth knowing mainly as a reason to be careful with fin wash near a hydroid: a slug that leaves the colony has to find its way back. The shape also means depth of field is the limiting factor in a photograph — the processes and the gill rosettes sit at different distances from the lens, and a frame taken square to the side keeps more of them sharp than one taken at an angle.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
