Phyllodesmium briareum - direct development?

February 18, 2000
From: Lindsay Warren

Dear Bill
I was wondering whether Phyllodesmium briareum skips the free-floating planktonic stage and develops in the egg case direct to a mini adult form.

In September 1999 [Tukang Besi, SE Sulawesi, Indonesia - Operation Wallacea] we repeatedly found large groups of P. briareum on Pachyclavularia violacea - two groups of 48, another of 67 and then smaller numbers together throughout October and November such as 21. On another occasion towards the end of September I found a group of over 107 in a 90cm x 54 cm area of what looked like Carijoa sp soft coral. Their size ranged from 10 mm - 35 mm. It just seemed a bit odd to think such large numbers of larvae had all been carried by currents to end up in such a small area.

Do you know the answer to this?
All the best
Lindsay Warren

100014.2112@compuserve.com

Warren, L., 2000 (Feb 18) Phyllodesmium briareum - direct development?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1919

Dear Lindsay,
I don't know of any studies on the life history of any species of Phyllodesmium. It would be a fascinating exercise and perhaps well worth thinking about as a project next season in Indonesia. If you have any aquarium facilities it may be possible to keep a small colony of the soft coral alive with 2 or 3 Phyllodesmium at least until they produced egg masses which could then be monitored.

Direct development is a possibility, but not necessary to ensure a concentration of young near the prey food. I looked at some species of coral-eating aeolids in fairly primitive conditions in Tanzania and found that they produced lecithotrophic larvae (non-feeding free-swimming larvae) some of which spent only a few minutes swimming before settling down. With one species, in a few weeks, from an original 6 adults I had 2 generations with thousands of eggs all on one small Porites colony. See pages on Phestilla lugubris, Phestilla minor and Cuthona poritophages.

That is not to say that veliger larvae, with a combination of luck and good chemo-sensory ability, are not extremely efficient at finding their preferred food. Another thing to realise as well is that different species of Phyllodesmium may have quite different life-history strategies. It is certainly worth following up if you get the chance.

Bill Rudman.

Rudman, W.B., 2000 (Feb 18). Comment on Phyllodesmium briareum - direct development? by Lindsay Warren. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/1919

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