Hypselodoris sagamiensis from Indonesia

October 17, 2007
From: F. & P. Pellet

Hi Bill,
After some hesitation, we have identified this nudibranch as Hypselodoris sagamiensis. We found it feeding on a black sponge (middle right photo). We would like to know if you agree with our ID.

Locality: Lembeh Straits, 12m, Indonesia, Celebes Sea, 26 09 2007, Sandy bottom . Length: 25 mm. Photographer: Francis Pellet.

We enclose also a picture of a 5 mm juvenile specimen (pic 3: depth 17m, Mawali Wreck, 28-Sept-2007) Could this be a juvenile of H.sagamiensis?

Thank you for your help once again.

Best Wishes
Francis & Pirjo


Pellet, F. & P., 2007 (Oct 17) Hypselodoris sagamiensis from Indonesia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/20976

Dear Francis & Pirjo,

This is a nice find. Yes I agree its H. sagamiensis which is very interesting because it provides a link between what we thought was the "home range" of this species in the Sino-Japanese region of the north Pacific and the large populations Gary Cobb [#19421] has reported from southern Queensland in eastern Australia. It looks like this species, rather than being endemic to the north-eastern Pacific has a wider distribution at least in the tropical western Pacific. As I discuss in Gary Cobb's message, this has an interesting similarity to the way the distribution of H. maritima , which was initially considered a Japanese endemic, was extended firstly to eastern Australia and then the intervening region was gradually filled in.

Concerning the juvenile. With the usual hesitation in identifying juveniles, I am pretty sure this is also H. maritima.

Thanks also for the sponge photo. Dark coloured sponges are always a problem to interpret from photos as much of the detail is lost in the shadows. It certainly could be a species of Euryspongia but I can't be sure. While concentrating on the detail, I almost missed the whitish mass on the right side of your feeding photo. As you can see in the close-up, it is the fibrous skeleton of a dysideid sponge - probably the same as the one the Hypselodoris is eating. Although I can't be sure, it seems reasonable to assume that this slug has eaten the first bit and has now moved on to the next bit - they may both be parts of the same colony. I think we can make a tentative determination that this species feeds on a dysideid sponge, possibly Euryspongia sp. This is the first indication we have of the feeding choice of this species.

I have also ringed a white spot on the edge of the mantle [middle photo]. This is one of the mantle glands which store distasteful chemicals from their sponge prey. In species of Hypselodoris and closely related genera the mantle glands are like this - discrete spherical or ovate sacs, quite different from the dendritic glands found in species of Chromodoris.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Oct 17). Comment on Hypselodoris sagamiensis from Indonesia by F. & P. Pellet. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/20976

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