Last week I gave you this largely amorphous blob to have a go at identifying:

Perhaps unsurprisingly it proved quite tricky, with most people opting for a brain, heart or gland of some kind. However, believe it or not, this is actually a whole animal.

In the comments a close suggestion came from palfreyman1414 who said:

“…invasive crab lip parasitical crustacean isolated…”

Tony Irwin clearly knew the actual answer with a nicely crafted cryptic link to the two common sequential hosts of this animal, the Flounder and the Cod. Meanwhile, on Twitter there were another couple of suggestions – one was a good general biological principle:

Every time I see such weird stuff, I now apply a new biology rule I discovered : “If it doesn’t look like any living organism you know, if you even doubt it’s a real organism, then it must be a parasitic copepod”.

I’m struggling to accept it though. THOSE THINGS ARE ABSURD.

— Le Crabe-Fantôme (@Crabe_Fantome) August 24, 2018

The other was a straight-up correct answer from Dr Ross Piper, an old zoological buddy from postgrad days and an aficionado of odd animals:

You’ve outstripped yourself with succulence this time. It’s Lernaeocera branchialis – one of the remarkable parasitic copepods.

— Ross Piper (@DrRossPiper) August 24, 2018

This is indeed a Codworm or Lernaeocera branchialis (Linnaeus, 1767) a type of copepod parasite that has a life history in which they spend part of their mobile larval stage parasitising flounders (and similar fish that sit around a lot) until they’re able to mate, at which point the fertilised female seeks out one of the mobile gadoid fish (the Cod family), where she gets into the gills and plumbs herself in to the Cod’s blood supply right at the heart, with her egg sacs at the gills and protected by the operculum (gill covers). She then spends the rest of her life sustained by fish blood, releasing eggs into the water and looking like a black pudding being eaten by maggots. Now those are life goals.

Adult female Codworm in Whiting gills. Image by Hans Hillewaert, 2006