Blue Sea Slug

May 6th – 12th 2013

Well did you guess what this week’s creature was?  For those of you who had it just on the tips of your tongue … let me put you out of your misery… its a Blue Sea Slug, also known as a sea swallow or a sea dragon!

Image source: wikimedia commons
Image source: wikimedia commons

Blue sea slugs float on their backs on the top of the sea, so the beautiful blue colours we see are actually the underside (foot) of the creature.  Their backs, submerged in the water, are actually a silvery-grey colour.  They are able to float due to a large sac in their stomach which they fill with air.It’s official name is a Glaucus atlanticus and it is a nudibranch (a shell less* mollusck). These little creatures usually only reach about three to four cm in size but don’t let that fool you…. they have a mean sting!  The blue sea slug preys on larger toxic sea dwellers such as the Portuguese Man O’ War (Physalia physalis).  It is immune to the stinging cells (nematocytes) within these creatures and is also capable of storing these deadly toxins within its own body and using them for its own defense.   The more venom it accumulates the deadlier its sting!

*Nudibranches may have shells during early stages of development but are shell less when fully mature).


Science blogger and writer; Owner of Dr. How's Science Wows; Mother of three junior scientists who have taught me that to be a great scientist you need to look at life through the eyes of a child!

2 thoughts on “Blue Sea Slug

  • May 8, 2013 at 9:49 am

    It was the colours that attracted me to it too Kim, just to draw it out I don’t reveal the answer until Sunday (a cruel streak in me!!) but I will always tell someone if they have guessed it right! Here are some clues though…it likes to float on the top of the sea, it goes by many names but one of them refers to a naked part of a tree (he he); another name refers to a land dweller that we all would prefer not to have in our veg patch!

  • May 8, 2013 at 9:33 am

    I’ve no idea but I love the colours! What is it???

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