Appearance
''Hypselodoris tryoni'' has a brown body and white foot. The body and upper dorsum are covered in purple spots ringed with white or light-brown. The gills are typically translucent white or light-brown and the rhinophores are brown to dark-brown and covered in circular white lines. It has a thin blue or purple line on the mantle edge. There is some colour variation between individuals.''Hypselodoris tryoni'' is similar in appearance to ''Goniobranchus geminus'', ''Goniobranchus kuniei'' and ''Goniobranchus leopardus'', although it lacks the wide purple mantle edge line present in those species.
Sea slugs such as ''Hypselodoris tryoni'', are known to exhibit trailing behaviour where up to four animals will follow one another very closely, often touching. It is not known what causes this behaviour.
''Hypselodoris tryoni'' reaches at least 60 mm in length.
Distribution
This species was described from the Society Islands. It is reported to occur widely in the tropical Western Pacific Ocean from Australia to the Philippines.
Habitat
Like many slugs in the family Chromodorididae, ''Risbecia tryoni'' feeds on sponges and have been seen feeding on sponges from the genus ''Dysidea''. When feeding they are sometimes accompanied by a species of shrimp, ''Periclimenes imperator'', in an apparent form of commensalism.
Evolution
The decision to include ''Risbecia'' species within the genus ''Hypselodoris'' was made on the basis of a molecular study which showed that ''Risbecia'' species are a clade inside the genus ''Hypselodoris'' as currently constituted.References:
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