Re: Strange lunch for Navanax

December 18, 2003
From: Ernie Hartt

Following on from your earlier comments I agree that Navanax don't seem to have any way of judging the size of their potential prey. In my master's research, I had one pair, both about 50 grams, in which one animal got the second about half-way down its gut, but could get it no further. At the end of my 3-hour observation period they were in the same position, so I "observed" them for another hour before returning them, still together, to a holding enclosure as I had to go to work, and my experimental protocol had been followed (they were observed in a 1 m square water tank, with flow through sea water about 10 cm deep, with natural bay sand substrate). I returned to the lab on my way home from work about 6 hours later to find the pair as I had left them. So I forcibly separated them, and put them in separate enclosures, even though the one that was being eaten did not look to be in good shape. But the next day, it was zipping around its enclosure, looking none the worse for wear.

I also had an attempt at cannibalism by an individual of less than 5 g on an individual if more than 100 g. Needless to say, the bigger Navanax reacted poorly, turned around, and gulped down the little guy, only to spit him back out for some reason.

Perhaps the strangest incidents were attempts at self cannibalism, which occurred while individuals were turning around; they at least demonstrate that Navanax can successfully follow slime trails to find prey, even if the prey is one's own tail!

Oh, and by the way, the gills on Navanax are posterior.

Ernie Hartt

Lumikko@snail-mail.net

Hartt, E., 2003 (Dec 18) Re: Strange lunch for Navanax. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11711

Dear Ernie,
Thanks for sharing these observations with us. Observations like this are often made by students in the course of their research but often are never published. Although in themselves they don't seem to be important, if we are able to accumulate enough of them they could provide us with useful background information which might just provide a missing link in someone's research or suggest a valuable line of inquiry.

Concerning its gills. In aglajids, such as Navanax, the shell is very reduced in size and lies internally at the posterior end of the body. The shell and the mantle cavity are of course closely linked, and in aglajids the gill, anus and female reproductive openings are all situated in a very reduced mantle cavity, opening ventrally at the posterior end of the body, beneath the shell.
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Dec 18). Comment on Re: Strange lunch for Navanax by Ernie Hartt. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11711

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