What is this black blob washing up on Australian beaches?

Earlier this year I was walking along the beach in Augusta, a tiny town in SW Australia, when I saw a frothy, smelly, gelatinous black blob washed up near by. Obviously I was intrigued.

My boyfriend’s father affectionately referred to it as a ‘sea fanny’, but I was suspicious as to whether this was it’s real name.

“Just don’t touch it.” said Dave. “They can kill dogs.”

Now I was definitely going to type sea fanny into Google later.

Can you guess what this black blob is? Photo: Anna Gardiner, Public Domain

Unsurprisingly ‘sea fanny’ did not turn up any lucrative results. So what was this black blob i’d happened across? Was it a jellyfish? A sea cucumber? A sea squirt? If you guessed any of these, soz but you are population wrongsville. And I will see you there, because these were my guesses too…

What it actually was, was Aplysia gigantea or the giant sea hare.

Err, what’s a sea hare?

Sea hares are marine molluscs. So, despite their jellyfish-like looking bods, they’re most closely related to other marine molluscs like sea snails, nudibranchs, squid, cuttlefish and octopuses.

They’ve got two flappy things called parapodial lobes which some can use to swim, and two little knobbly horns on their heads called rhinophores. These contain chemoreceptors that help them smell, taste, and because they look like tiny ears, also give them their sea hare name.

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Couple o’ traits to spot on the the giant sea hare. Photo: Anna Gardiner, Public Domain
A swimming giant sea hare! Photo: Stephen Clifford

Sea hares inhabit shallow marine waters right around the world and the giant sea hare is naturally, one of the largest. It can weigh up to 2kg and grow to the size of your bed pillow (60cm in length)! Imagine resting your face on a cold, squishy, giant sea hare… Found from Esperance right up to Shark Bay in Western Australia, these strange looking animals lead a life that’s just as odd as their appearance.

Sexy conga lines

When it’s time to mate the giant sea hare basically forms a sexy conga line. All sea hares are hermaphrodites, meaning they have both female and male reproductive organs. When mating, up to 10 individuals can commonly be found passing and recieving sperm along a line. The front sea hare will act only as a female, the last sea hare will act only as a male – and all those in between will act as both!

During the warmer months the sea hares will lay their eggs through their genital groove, a structure found in their neck. This means that yes, sea hares lay eggs from their neck. Consequently, by shaking their head a string of long cylindrical eggs can be deposited, with A. gigantea usually leaving them attached to seaweed.

A. gigantea, the giant sea hare, found washed up in Augusta. Photo: Anna Gardiner, Public Domain

Poisonous package

The giant sea hare typically lives for one year only, with masses washing up on beaches at the end of their lifecycle. The problem is that the giant sea hare is poisonous when ingested by dogs and one study, based in Geraldton, reported 72 dogs poisoned by the giant sea hare between 2001 and 2011. Seven of which died. The poisoning may be as a result of chemicals present in the digestive gland of the sea hare – so make sure if you do see this odd black blob, you don’t let your dog touch it!

So, while it may be an unfortunately poisonous package when washed up, the giant sea hare has a lot of good going for it too. It swims with wing-like lobes, mates in a line and lays eggs through it’s neck! This is one HARE raising odd organism. Yep. Went there.


Carefoot, T. H. (1987). Aplysia: its biology and ecology. Oceanogr Mar Biol, 25, 167-284.

Peacock, R. E., Hosgood, G., Swindells, K. L., & Smart, L. (2013). Aplysia gigantea toxicosis in 72 dogs in Western Australia. Australian veterinary journal, 91(7), 292-295.


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