Chromodoris petechialis still missing

January 21, 2002
From: John Hoover

Hi Bill,
In your reply you ask if any new information about Chromodoris petechialis has turned up. You can be sure that if I seen or hear anything more of these slugs you'll be the first to be notified.

In an earlier message, Scott Johnson suggested that they might live primarily in deep water -- an interesting idea. Related is the possibility that their population center lies in the uninhabited Northwest Hawaiian Islands. Animals found in deep water around the main Hawaiian Islands often occur shallower in the northwestern chain because the water there is cooler.

Unfortunately, almost no diving or collecting takes place in the Northwest Hawaiian Islands except around Midway Atoll. Midway has been surveyed for opisthobranchs several times, but suppose these particular slugs are nocturnal? That would greatly lower the chance of finding them because the northwest islands, especially Midway, are prime tiger shark territory. I'll bet NO ONE goes out diving or snorkeling there at night!

Another possibility is that C. petechialis was endemic to Kaneohe Bay and perhaps Pearl Harbor, both on Oahu. Believe it or not, these two are the only extensive, well-protected, lagoon-like bodies of water in the main Hawaiian Islands. Perhaps C. petechialis fed only on a sponge inhabiting Kaneohe and Pearl -- both these bodies of water appear to have a greater concentration on variety of sponges than most Hawaiian habitats. Since Gould's and even Zahl's day both have had their ecologies greatly disrupted. Among other things, exotic sponges from all over the world have been introduced by shipping. It's not inconceivable, therefore, that some native sponges preyed upon by C. petechialis were displaced and driven extinct by introduced sponges. And with them might have gone the beautiful red-spotted slug.

Since that's a depressing thought, let's hope the first scenario is the correct one! There is still much to be learned about the Northwest Hawaiian Islands.


Hoover, J., 2002 (Jan 21) Chromodoris petechialis still missing. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks John,
My thoughts were that Zahl probably photographed animals from Kaneohe Bay which was the focus of his article. I'm afraid the published photo in National Geographic Magazine seems to show green filamentous algae in the background behind the anchor chain which would suggest pretty shallow water. I guess we can only just keep our fingers crossed that it turns up somewhere
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Jan 21). Comment on Chromodoris petechialis still missing by John Hoover. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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