Small, striped lengthwise in fine brown lines, sprinkled with blue spots in dark rings and covered in branched papillae that blur its outline into the mat it sits on. Rarely more than 6 cm (2.4 in), and almost never alone: where there is one there are usually dozens.
The food explains the crowds. This sea hare specializes in cyanobacterial mats, the slick dark films that spread over sand and dead coral in warm still water, and a bloom of the mat is followed by a bloom of the animal. Reefs with a cyanobacteria problem often have a temporary population of these grazing it back.
That diet has consequences. The cyanobacteria are loaded with defensive toxins, and the sea hare stores them rather than breaking them down, which makes it distasteful and makes it a well-studied source of interesting molecules. Eating the inedible and wearing it as armor is a strategy this whole group has committed to.
- small slug striped lengthwise in brown, with blue spots ringed dark
- body covered in fine branched papillae
- often in dense aggregations on mats of cyanobacteria
- length up to 6 cm
