Friday, March 5, 2010

How to tell if it is a Janolus.

Our species list now contains two Janolus.

With a profusion of cerata on their dorsum Janolus could easily be mistaken for an aeolid, but in belonging to the Zephyrinidae family the Janolus are armininans not aeolids. Although having an aeolid-like form the most readily observable feature of distinction is that in the Janolus the cerata continue uninterrupted around the anterior margin of the head, a feature no aeolid possesses (refer pic above, from The Collection). A further helpful attribute of distinction is the location of the anal papilla. In Janolus it is located on the dorsal midline posteriorly (see Erik Schlogl's message at ), whereas in the aeolids it opens to the right anterior quarter usually on the side. Whilst the rhinophores are non-retractile in both the Janolus and the aeolids, the Janolus possess a distinctive ridge between the rhinophores at their bases. This longitudinal ridge is called a caruncle and its purpose is unknown, although some have variously suggested it performs a sensory or defensive purpose.