Philinopsis cyanea hunting Stylocheilus

June 20, 2005
From: Mike Roberts

To accompany my message [#14074] on Stylocheilus swarming in Hawaii, here are some photos of one of the predators I observed eating them. 

Locality: Ulua Beach, Wailea, Hawaii (Maui). Depth: 40-50 ft. 05 and 06 May 2005. Sand. Photographer: Mike Roberts

There were literally thousands upon thousands of Stylocheilus forming rivers of slugs climbing on top of each other with a definite plan of going south.On an even closer inspection the individual slugs could be spotted in all sizes from large - for a sea hare anyway - to those that seem freshly hatched.Cute little guys but they were the hors deuvres of the day. Stripebelly puffer fish just rested next the line of food, looking like so many Jabas while gorging themselves well beyond capacity.

Then I saw a nudi I had never seen before. He was a mean machine with body lines that would make Fisher jealous. He was certainly built for speed! This efficient little machine was just zooming along in haphazard patterns until he caught the "scent" of a hare in his path. Then, without missing a beat, the hare would be sucked into his powerful manifold and he would move on to the next one.

Even though there were dozens of these sleek nudis driving around in circles and slurping up the little morsels, even though the puffers stationed along the rivers were too fat to swim, the hares didn't seem to understand they were lunch. But it didn't matter in the big scheme. They had numbers on their side. And they just kept marching south.

Mike Roberts

Roberts, M., 2005 (Jun 20) Philinopsis cyanea hunting Stylocheilus. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Mike,
Thanks for this great observation - and your graphic description of it. The white lines at the front of the head ar on a swelling on each side of the mouth which is covered in sensory bristles which sense the mucous in the trails of their prey. They have no teeth so they feed by partially everting their large muscular buccal bulb and by a combination of suction and envelopment drag their prey into their large sac like crop, where it is digested. Your description of the puffer fish and Philinopsis lurking around the edge of the mass of Sea Hares reminds me of the the lions and hyaenas picking off prey during the mass migrations of herbivores in the grasslands of East Africa - but I hasten to add that this isn't proof that what we are seeing is a migration.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Jun 20). Comment on Philinopsis cyanea hunting Stylocheilus by Mike Roberts. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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