Join me in the cold, dark, life-sustaining NE Pacific Ocean to discover the great beauty, mystery and fragility hidden there.

Preoccupied with Parasites

Preoccupied with parasites!

That’s not usually a good conversation starter is it?

But, read on. It’s worth it! If you are fascinated by adaptations and the interconnectedness of species . . . even when it involves parasites.

These are Transparent Tunicates (aka Transparent Sea Squirts). They are not parasites. They are highly evolved animals with a primitive backbone. They take in food particles through one siphon in their strong “tunic” and expel waste through the other siphon. See the siphons?


The dark you see here is the waste inside their rectums. Yep, they are filter feeders and clearly take in some sand too. What’s this then about parasites?

This species gets invaded by a wicked parasite (as opposed to all those gentle and meek parasites out there) . . . the Spotted Flatworm! This species of flatworm curls up, sneaks in through the tunicate’s branchial siphon, unrolls, eats the tunicate’s internal organs over 3 to 7 days and then moves on, leaving behind the empty tunic.

They are species specific parasites, apparently specializing in invading Transparent Tunicates. The following photos clearly show you the Spotted Flatworm presence there and the tunicates are now mere shells of their former selves.

All the internal organs are gone in the heavily invested individual in the photo below.


In having the privilege of learning even from individual animals by diving the same areas frequently. I recently saw the progression for individual Transparent Tunicates and the Spotted Flatworms that had invested them. The following photo is from March 1st, 2020. I’ve now added arrows to show the parasites.

The following two photos show you reality  24 days later. The originally invested Transparent Tunicates are dead and the Spotted Flatworms have moved into their neighbours.

Below is another perspective on the same individuals.


I truly hope that in these times where our own species is facing extreme challenges, that this information still creates awe, connection and respect for the lives of others. Maybe it’s more important than ever.

Wishing you health, resilience, and strength of community.

Transparent Tunicate = Corella willmeriana to 7.5 cm.
Spotted Flatworm = Eurylepta leoparda to 2.5 m.

2 Responses to “Preoccupied with Parasites”

  1. Jody McConnan

    Thank you Jackie for this wonderful look at ‘parasites’ – I am in awe at how biologists ‘figure it all out’ with re who is who, who invades who, who is the host, the predator, the good guy, the not so good guy, and so on – it boggles my mind! I’m just so thankful that someone – like you – studies these incredible species – you are indeed fortunate to frequent a site often enough to observe, and blessed with living in this incredibly diverse place you call ‘home’. Just look at the list of all the ‘reading’ material & photos everyone can spend a little of their isolation time viewing and reading: who needs to go to school, it’s right here at our fingertips!


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    • The Marine Detective

      I really value this feedback Jody. It’s sometimes difficult to know the “worth” of posting the content (not that it would stop me). This provides a boost of affirmation.


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