Giant-mouthed shrimp-eating sea slug

November 14, 2007
From: Katie LeFevre

October 10, 2007
During a nighttime excursion, this little guy (~2 inches) "swam" (by turning on its side and bending back and forth) up in the water column after its large (2ft tall) clump of algae was moved around (we were looking for other things inside it). The area is a very calm intertidal zone (boat dock bay area), we were there at low tide and so the slug was about 1-2 feet underwater.
I've never seen one like before so I was able to take him back to our lab and get some close up photos under a scope before we took him back.

Locality: Kaneohe Bay Boat Docks, 2 feet, Oahu, HI, USA, Indo-Pacific, 10 October 2007, Sludgy/sandy Calm Intertidal. Length: 2 inches. Photographer: Katie LeFevre.

What struck me first as unique was his mouth... which made me think of a little kid's worst nightmare. It's wider than any other part of his body and he crawls around with it open. As he crawled along the algae, he would randomly put his mouth around an branch of it and close tightly. Then you could see a "throat" area just behind his mouth flex -- like it was swallowing. The inner 'tentacles' of his mouth ring could move independent of each other and seemed to be tasting the area. AND at one point I could have sworn I saw an amphipod struggling in his mouth.

Very curious now, I put a tiny mysis shrimp chunk in front of him and to my surprise, he closed his around it "grabbed" it with his "throat" and didn't open his mouth until it was engulfed inside him.
Is there a certain group of slugs that eat other things than coral/sponges?? There are lots of sponges in the area, yet.. he ate the shrimp?

His body was detailed, you can see the lattice patterns in his skin. He had 5-6 big, bulbous cerata that were randomly spaced, but actually were shed when he was bothered (noticed one of that when I poured him into a viewing dish) and that could be the cause of spacing. The translucence and spiked texture made him blend in with all the algae perfectly like a piece of sludge.

Previously found in the same area was a Polybranchia orientalis --which also exhibited cerata shedding behavior.

The attatched pictures show his head, eyes and "throat" (dark area in middle of mouth), mouth closed around algae (there's a baby swimming-anemone right in front of him), and his tail end.

I hope you can at least give me a lead on what group of slugs he belongs to, or how I might identify him.

Katie LeFevre
Brigham Young University-Hawaii
Marine Lab Manager

LeFevre, K. D., 2007 (Nov 14) Giant-mouthed shrimp-eating sea slug. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Katie,

'Giant-mouthed shrimp-eating sea slug' - now that's a descriptive name which well descibes this fascinating animal. It is Melibe engeli, one of a group of species which have lost their teeth - and all the associated structures - and feeds on small crustacea by using their fishing-net like mouth to 'feel' out prey and scoop them up. Have a look at the Fact Sheet for this species and associated messages for further information.

Dropping body parts, as you describe for this animal, is a defensive technique used by quite a number of unrelated opisthobranchs [see Autotomy page]. It's usually accompanied by sticky glandular secretions which cause the 'spare part' to stick to a predator's mouth long enough to distract it from eating the rest of the slug.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Nov 14). Comment on Giant-mouthed shrimp-eating sea slug by Katie LeFevre. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Melibe engeli

Related messages

  1. Melibe engeli and its oral hood
    From: Charles Raabe, October 27, 2008
  2. Melibe engeli - aquarium hitchhiker
    From: Can Tunali, May 2, 2008
  3. More on Melibe engeli
    From: Jung Eun Yoon, July 5, 2007
  4. Melibe engeli from the Philippines
    From: Jung Eun Yoon, May 25, 2007
  5. Melibe with eggs from East Timor
    From: Brian Francisco, December 7, 2006
  6. Melibe sp? in my aquarium
    From: Michael Biester, February 15, 2006
  7. Re: Hitch-hiking Melibe engeli
    From: Todd Gardner, February 1, 2004
  8. Hitch-hiking Melibe engeli
    From: Joe Yaiullo, January 30, 2004
  9. Melibe engeli - dextral egg spiral
    From: Bill Rudman, March 6, 2003
  10. Melibe engeli in aquarium
    From: Andrew Trevor-Jones, January 28, 2002
  11. Melibe engeli from Japan
    From: Atsushi Ono, March 5, 2000
  12. Re: Melibe sp. from S.E. Sulawesi
    From: Terry Gosliner, March 3, 2000
  13. Melibe from SE Sulawesi
    From: Lindsay Warren, February 29, 2000

Show factsheet and all related messages