Tuesday, May 09, 2017

Shag-rug nudibranchs

It's egg-laying season. I disturbed a nudibranch busy gluing her strings of eggs to a rock.

Aeolida papillosa, with fresh eggs.

When I turned over her rock, she left the eggs and went down to join another nudi on the sand.

They twisted and turned together, facing first one way, then the other.

Shag-rugs are also known as shaggy mouse, or grey nudibranchs. The colour varies from brown, grey, orange, and even purple, depending, in part, on their diet.

The two brown "horns" are rhinopores, sensory organs that detect scent and taste in the water. At the very front of the foot (like a snail, the nudibranch is a monopod, travelling on one broad foot.) two more projections, called pedal tentacles. All the other waving spikes are cerata.

These nudibranchs eat various anemones. They collect the stinging nematocysts from the anemones' tentacles, without getting stung themselves, and move them into the tips of their own cerata, ready to sting anything that thinks a soft, fleshy slug would be good eating.

It is said to be a voracious predator, consuming enough anemone tissue to equal half or all its body weight per day. (Wallawalla.edu)

More shag-rug eggs, with clamshell and crab.


  1. Would a nudibranch pose a danger to your tank's anemones, if one came in with the seaweed? Or do they target specific species of anemones?

    1. Yes, one of these shag rugs, anyhow. They like anthopleura elegantissima, of which I have 5, and the big metridium that you caught for me. I think the burrowing anemone would be safe.

  2. Perfect name. Except for the colour it looks just like the shag rug I had in the first apartment after I got married in 71. - Margy


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