Observations on Philinopsis taronga in NZ

June 3, 2003
From: Paul Furneaux

Hi Bill,
Thanks for all the information on Philinopsis taronga since my first message. Since I first came across Philinopsis (April 13th) I have been out on the mudflats in that same general area four times - 28th, 29th April, and 28th, 29th May. On all four occasions I counted several individuals of P. taronga; 11 individuals on April 28th, about 30 individuals on April 29th. The interesting thing about these individuals on both days is that they were mostly lighter in colour than the ones I photographed in mid April. The other interesting point was that they seemed to have been very busy reproducing and hopefully my photos will show this.
• 1. They seem to secrete a mucus wrap or envelope about themselves when they mate.
• 2. Their egg masses are large/long(4-6cm) and contain whitish coloured eggs.
• 3. The egg masses are anchored into the mud by "branches" of mucus at one end of the mass.
• 4. the egg masses are very often set out in pairs (one photo shows two animals depositing their egg masses) as though after mating they deposit their egg masses almost immediately.
• 5. I counted about 20 to 30 egg masses on April 28th and about 50 egg masses on April 29th. I found the egg masses over a much greater area than I did the animals themselves.
By May 28th and 29th the numbers of both the animals and the egg masses had fallen away to 4 and 7 animals and about 15 to 20 egg masses each day.

PHOTOS: Upper right: Showing 2 animals on left egg laying and another animal on right following mucus trail. Lower left: animal [on left] and egg mass [centre]. Lower right: Animals mating - upper 2 in mucus cocoons.

I must say that I never realized that "sea slugs" could be so interesting or exciting and I probably have to admit that I have "caught the bug". I spoke to a group of high school teachers recently about my work and extolled the virtues of the Sea Slug Forum, and as biology educators they are in a position to encourage young people to become involved in this sort of thing. Anyway I hope that the photos are useful, I'll send the other species over soon.
Regards,
Paul Furneaux.

P.Furneaux@xtra.co.nz

Furneaux, P., 2003 (Jun 3) Observations on Philinopsis taronga in NZ. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/10140

Thanks Paul,
P. taronga certainly seems a lot more abundant in Tauranga than it ever was in Auckland. Now that you have developed an 'eye' for seeing Philinopsis it will be interesting next year to see if you can find them at a much smaller size, perhaps a few months earlier in the year. The mucus 'cocoon' they form while mating is I think just a consequence of their design. There whole body is covered in microscopic hairs [cilia] which beat in rythym. At the front of the head are large mucus glands which secrete copious amounts of mucus most of the time. So when the slug is crawling along it is really being slid along through a tunnel of mucus ny these fine beating cilia. The mucus of course picks up the fine sand and silt particles which we can see in your photos makes the mucus 'tunnel' quite opaque. When the animal is not crawling along - such as when it is mating - the mucus is still being produced so the result is they mating pair end up in a big cocoon as you describe. As you desribe the egg masses are anchored in the sediment by long branched mucus filaments.

I am gad to hear than your later finds of Philinopsis have been lighter in colour. Seeing the yellow markings in the photo alongside certainly comfirms the identity of your animals. I look forward to further observations - and am glad you've 'caught the bug'.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Jun 3). Comment on Observations on Philinopsis taronga in NZ by Paul Furneaux. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/10140

Factsheet

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