Dear Sylvain,

If those two species are different, then the diagonal purple lines on the mantle would suggest it is H. nigrostriata. In the other species the lines are said to be parallel. Your photo is another nice record of this species feeding. Although we have earlier records of it , and H. zephyra, feeding on this purple species of Dysidea, the more records we accumulate help to confirm its feeding preference.

Best wishes,
Bill Rudman

Dear Art,

The main difference between Hypselodoris nigrostriata and H. zephyra is that the former has dark lines which cross diagonally, while in H. zephyra the lines are mainly parallel. Although in the Indian Ocean the rhinophores of H. nigrostriata don't seem to have a white tip, in the Indonesian region we have quite a few examples on the Forum with a white tip. As I have discussed before, the difference between these two species is debatable.

I would call your animal H. nigrostriata. We don't have much information on feeding in that species but both species seem to feed exclusively on a bluish sponge of the genus Dysidea. One of your animals has its oral tube everted and is clearly feeding on the same sponge. Compare it with message #21093 showing H. zephyra feeding. This is a nice additional bit of information on its natural history.

Best wishes,
Bill Rudman

Dear Will,

Thanks for clearing the blue colour up - the hull is a good colour match for the sponge they usually eat. In this photo I can see the other nudibranchs and they certainly look as though they are all feeding. While I am happy to accept the blue in the top half of the photo is the hull, I am pretty sure the bluish objects I have circled are small parts of a sponge colony. Unfortunately I can't poke around in the photo to check - and even if I could, it is often very difficult to find or identify these sponges as they can be covered or tangled up in other animal and plant growths.

Best wishes,
Bill Rudman

Dear Will,

Thanks or the photo. I can only see one animal in your photo, were the others you mention nearby? One point of interest are the blue patches in the background. I suspect they are parts of a large colony of the sponge Dysidea sp. which this Hypselodoris feeds on. If there were other H. nigrostriata nearby, I guess they were all attracted to the sponge. Have a look at Yahia Mokhtar Hafez's message [#21264] showing the sponge in more detail. It also shows similar soft corals as well, but I preseume that is just a co-incidence.

Best wishes,
Bill Rudman

Dear Yahia,

Thanks for the extra photos of the Dysidea. The Hypselodoris has certainly found a little patch of its favourite food.

Best wishes,
Bill Rudman

Dear Yahia,

This is Hypselodoris nigrostriata. Of particular interest to me is the bluish sponge with the whitish network of fibres in the bottom right of your photos. This is the remains of a sponge colony [Dysidea sp] which this species is known to eat, so it is a useful confirmation of this nusibranch's food choice.

Best wishes,
Bill Rudman

Dear David,
The first time I found this species, I found a single animal with a single specimen of Hypselodoris kanga. By some amazing chance their larvae had found the same colony of sponge growing on a small concrete pipe in the middle of a sandy beach. The pipe was an outlet pipe from the University of Dar es Salaam's marine station in Tanzania, where I was working at the time. It is Hypselodoris nigrostriata and as one animal was an unnamed species and the other hadn't been seen since its original description almost 70 years before, I too wasn't sure if I had two species or two variations of one species.

Both have the same basic markings and both have gills which are triangular in cross-section but in H. nigrostriata the dark blue lines are long and often diagonal, the yellow patches are large and irregular in size and shape, and the gills are lined with red. In H. kanga, the dark blue marks are usually spots or very rarely, short lines, the yellow spots are small and regular in shape and the gills are lined with red and blue, and there are usually yellow spots along the outer face of each gill. Your animal is what I would call a 'typical' H. nigrostriata. I often comment on the difficulty I have at times separating this species from H. zephyra, a species which is even more similar in colour than H. kanga. In H. zephyra the dark blue lines usually run parallel to each other rather than crossing diagonally, and the gills appear to be simple in shape rather than triangular in cross-section. Unfortunately often in photos the gills are slightly unfocussed and its not possible to determine whether they are simple or triangular so H. zephyra and H. nigrostriata often cause me trouble in photo identifications.

In both these photos and those of  Hypselodoris regina [message #21141 ] your animals are crawling in an area with many colonies of an orange sponge which I doubt is their food.  Supporting that idea is the fact that in all the photos the slugs seem to be avoiding the orange-red colonies.

Best wishes,
Bill Rudman

Dear Francois,

I am pretty sure this is Hypselodoris nigrostriata, but I find it pretty difficult to distinguish it from H. zephyra.  As you will see from comments I have made in messages concerning both species I have some doubts about whether we are dealing with one or two species here.

Of more interest is that these two animals are feeding on the dark blue sponge. The oral tube of the animal on the right of your photo is clearly visible. The sponge is almost certainly a species of Dysidea, and probbaly the same species as H. kanga is eating in your message #20778.

Best wishes,
Bill Rudman

Dear Fabrice,
Yes this is a chromodorid. It is Hypselodoris nigrostriata, and like other animals of this species from the western Indian Ocean it has much more prominent yellow markings than found in specimens from further east. It also appears to be feeding on, or at least interested in, the grey-blue sponge which seems to cover quite a bit of the substrate, and be partly overgrown by branching coralline algae. The sponge appears to be a dysideid sponge which this species has been reported on before [#9500, #6017 ]

Best wishes,
Bill Rudman

Dear Colin,
Yes this is H. nigrostriata. As often occurs, the sponge it is obviously feeding on his hidden under a layer of sand and detritus. Most nudibranchs develop their colour pattern as they grow. When they first become small crawling slugs they are a pigmentless and translucent, but grdually they begin to develop the pigmentation characteristic of their species. For this reason it is often impossible to confidently identify juveniles to species level
Best wishes,
Bill Rudman

Dear Bruce,
This certainly appears to be H. nigrostriata to me. In Hypselodoris zephyra, the black lines are said to be parallel rather than oblique.
Best wishes,
Bill Rudman

Dear Danny,
I think this is Hypselodoris nigrostriata. See my comment on your earlier message as it is diffiult to distinguish from Hypselodoris zephyra. It looks as though it is eating a brown-yellow sponge in the lower photos.
Best wishes,
Bill Rudman

Dear Sarah,
Some species of Hypselodoris do look quite like a species of Nembrotha, but they feed on ascidians, and happily your photo shows the animal feeding on a sponge. The brightly coloured cone sticking out the front of the animal is the oral tube which usually lies inside the 'mouth'. Only when feeding is it pushed out so the feeding apparatus - the jaws and radula - can make contact with the sponge food. This animal is Hypselodoris nigrostriata, and as far as I know this is the first information we have on which sponge it eats.
Best wishes,
Bill Rudman

Dear Danny,
This is the eastrn Indian Ocean form of Hypselodoris nigrostriata. It differs from the similarly coloured H. zephyra in that some of the purple lines are diagonal, and the gills are triangular in cross section. In your two lower photos you can see the two orange lines along the outer edge of the gills.
Best wishes,
Bill Rudman

Dear Sabine,
Yes I would call these Hypselodoris nigrostriata.
Best wishes,
Bill Rudman

Dear Mary Jane,
I would certainly consider this to be Hypselodoris nigrostriata.
Best wishes,
Bill Rudman

Dear Stuart,
I am pretty sure these are Hypselodoris nigrostriata. Have a look at my comments on other messages on this page. Form them you will see that I have some difficulty separating this species and to see Hypselodoris zephyra.
Best wishes,
Bill Rudman

Dear John,
Thanks for these photos. Both the colour variation and the food are very interesting. I have included an enlargement of the head (lower left) showing the multicoloured oral tube extended on to the surface of the sponge - a sure sign of feeding. I am afraid I find it more difficult to differentiate between H. nigrostriata and H. zephyra everytime I see some photos of another specimen.
Cheers,
Bill Rudman

Note added 21 March 2003: The triangular gills make me think this is probably H. nigrostriata. See message.

Dear Rie,
I think this is H. zephyra but as I have discussed before, I am having difficulty separating that species from H. nigrostriata. I thought H. zephrya had simple gills while H. nigrostriata has gills which were triangular in cross-section. Mr Tanaka's photo shows triangular gills which would make this animal H. nigrostriata. Howvere I need to check whether the gills of H. zephyra are indeed 'simple' or are also triangular. I have discussed this problem in an earlier message but am still not clear how to separate these two species from photos. Sorry I can't give you a definite answer at this time

Best wishes,
Bill Rudman

Dear Valda,
This is indeed Hypselodoris nigrostriata.
Best wishes,
Bill Rudman

Dear Gordon,
Another interesting find. There are a group of similarly species in the Indian and Pacific Oceans and until we have a better idea of colour variation in different parts of the world it is difficult to decide whether different colour patterns are restricted to different geographic areas.
Best wishes,
Bill Rudman

Dear Clinton,
Erwin is right. It is what I'm calling H. nigrostriata. It is quite similar to the recently described Hypselodoris zephyra but in that species the gills are a uniform orange, and the lines on the mantle are usually parallel not diagonal as in H. nigrostriata.

[Clinton has a website called Metridium Fields which is well worth a look. It includes photos of a number of nudibranchs from Monterey, California.]

Best wishes,
Bill Rudman.

Dear Wayne,
Good question. The short answer is I don't think so. Hypselodoris zephyra, which was described after your message, is certainly very similar but there is one major point of difference, and that is the shape and colour of the gills. The gills of H. zephyra are described as 'simply pinnate' and uniformly orange, whereas the gills in H. nigrostriata are triangular in cross section. This can be clearly seen in your photo because the two outer corners of each gill are lined with orange (as of course is the inner edge). The rest of the gills are white or faintly translucent orange.

When I looked at your photos again just now, I thought that your animal was H. zephyra, and it is certainly very similar to Vinka Stenhouse's photo of H. zephyra from Vanuatu, but if you look at the gills of her animal they are simple and uniformly orange. The white spots or glands? up the outer edge of the gills in your photo are not present in specimens from East Africa but overall I would say your animals are H. nigrostriata.

One other difference between the two species is that in H. nigrostriata the mantle glands are small and are found all around the mantle edge except for a small region midway down each side. In H. zephyra there are a few large posterior glands and a few small anterolateral glands - none laterally. I can't be 100% sure but it seems to me that in your photo, the way the mantle sits would suggest small glands along the left edge of the mantle, typical of H. nigrostriata - though that may just be wishful thinking on my part.

It would certainly be interesting if both species co-existed along the boundary of the Indian and Pacific Oceans. Any views welcome.

Bill Rudman.

Dear Mike,
I've put the Hypselodoris kanga photo on the appropriate page. They fill a gap in the known distribution.
Thanks,
Bill Rudman.

Dear Wayne,
I looked through my files and found another photo of yours which seem to be of the same animals. If I said Nembrotha I must have been having a bad day, as your animal is Hypselodoris nigrostriata. It is one of a group of species of Hypselodoris in which the body has indeed taken on the look of a nembrothid, with a narrowing of the mantle skirt and a heightening of the body. With further study we may decide that the Indian Ocean and Pacific colour forms are consistently different enough to consider separate species but more material from the Indonesian Archipelago and up to Thailand will need to be studied.
Bill Rudman.