Gymnodoris nigricolor Is a tiny nudibranch that attaches to the fins of gobies. It is found in the winter months and then it seems to completely disappear when the water warms up. This nudibranch is by far the hardest to photograph because of its size and it stays attached to it’s host. When the goby feels threatened, it retreats into its burrow taking the tiny slug down the hole with it.

In order to photograph sand-dwelling gobies you will generally need a 50mm-100mm macro lens.

Be patience and move slowly. If your lucky the goby will accept your presence without retreating.

February 2018, I was fortunate to find Gymnodoris nigricolor crawling on the sand in search of a host

When the slug finds a host it will attach onto the closest fin.

Look close and you can see the buccal apparatus of the slug clamping down.

Once its locked down, the goby cannot shake the slug off.

No one really knows what happens next. Why does the nudibranch attach to the fins of its host？ Does this specialist feed on only the fins of gobies or is there another reason？

If you would like see stunning photographs of more sea slugs check out my post on nudibranchs

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