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October 2020

Rock pool cruiser

My grandchildren found this little creature amongst the rocks on the headland at Caloundra yesterday. Would it be possible to identify the creature from this video?

An Indo-Pacific Black-ringed Sea Hare forages in a Sunshine Coast rock pool. Video courtesy of Kevin Price.

Answer

Our curator of molluscs has identified the animal in the video as an Indo-Pacific Black-ringed Sea Hare (Aplysia argus). Until recently this species was known as Aplysia dactylomela, which is actually an extremely similar, but genetically distinct, Atlantic species. Sea hares are large (commonly 20-30 cm long, but can grow to 45 cm) sea slugs that graze on algae in shallow coastal waters. All sea slugs are gastropods (the largest class of molluscs that also includes snails and land slugs), and are distinguished by having a reduced or absent shell, gills positioned on the rear of the body, two tentacles above the mouth, a pair of small eyes, and two tubular tentacles behind the eyes. Aside from these features, sea slugs display a great variety of forms and lifestyles, from microscopic algal grazers to large free-swimming predators. Sea hares are among the largest sea slugs, with two pairs of tubular antennae and two lateral body flaps (called ‘parapodia’) that are held over the body. While many species of sea slugs are famous for their bright colours, sea hares tend to have colour patterns suited to camouflage. This isn’t their only defence against predators, however, as many species can also release a cloud of ink (produced by the appropriately-named ‘repugnatorial glands’), just as many cephalopods do. Some species of sea hare are also able to use their parapodia as fins, allowing them to swim away from danger, or perhaps take advantage of tidal currents to relocate.

Sea hares are hermaphrodites (each individual is both male and female), and during the breeding season they can congregate in large numbers. They famously produce an incredible number of eggs; one individual may lay tens of millions of eggs in long gelatinous strands.

Want to know more? Our Discovery Centre is a free service open seven days per week, with experts ready to answer your questions. You can phone, write, or contact us via our website. If we don’t know the answer we will try to find out for you.

 
Indo-Pacific Black-ringed Sea Hare, brandishing its four tubular antennae. Photo: Gary Cranitch, QM.

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