How to tell seguro-ryugu-umiushi and kurosuji-ryugu-umiushi apart

Jun 15, 2026 ·

Someone asked me how to separate seguro-ryugu-umiushi and kurosuji-ryugu-umiushi, so writing it down here.

seguro-ryugu (Nembrotha sp.)
seguro-ryugu (Nembrotha sp.)
kurosuji-ryugu (Nembrotha sp.)
kurosuji-ryugu (Nembrotha sp.)

Look at the red-circled area (face and gill base):

  • Face and gill base are the same body colour (cream?) → kurosuji-ryugu-umiushi
  • Face and gill base are pigmented → seguro-ryugu-umiushi

Caveat 1

I'm writing this without consulting the papers, so this is approximate. It's the convention from a certain field guide.

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