Olive Sea Hare

Elysia expansa

The olive sea hare is a sacoglossan, a sap sucking mollusc, and is one of 70 described species in the family Placobranchidae (once known as Elyssidae).  Species in the genus Elysid have an elongate, narrow body, and on either side of their body are large wing-like structures called parapodia which can be used for locomotion.  They have a discrete neck and a head with a pair of sensory tentacles, known as rhinophores.  It is these rhinophores that have given this animal their common name, as they resemble the ears of a hare.  The body of the olive sea hare is green in colouration, which is derived from ingested algal chloroplasts and a thin black line extends along the margin of the parapodia.  The parapodia have a ruffled appearance and are very large in comparison to those of other species in the family.   If threatened these animals can expel a cloud of deep purple ink that acts as a smoke screen, enabling them to escape from predators.

The olive sea hare lives in shallow water habitats, living in association with the green algae Caulerpa racemosa and Caulerpa cupressoides upon which they feed.  They occur commonly along the south west coast of Australia from the Houtman Abrolhos Islands south to Geographe Bay though often remain undetected in their habitat as they are very well camouflaged.  Sea hares live for approximately one year and form long chains when mating.  In late summer they lay egg masses resembling long, yellow, spaghetti-like strings.  The olive sea hares grow to a maximum length of 30 millimetres.

 

Occurrence at the Busselton Jetty:

The olive sea hare can occasionally be observed through the windows of the underwater observatory.  Due to their cryptic nature and excellent camouflage they can be difficult to spot amongst the invertebrates on the piles.  The olive sea hare has been observed, attached to the pile with its muscular foot, while the upper half of its body is unattached and swaying with the water current, appearing to mimic a mass of algae.

Image by: A.Brown