Dear Thad,

Thanks for the photo. From other photos I have seen, it looks as though this species loses the white band around the edge of the mantle at it grows larger. Your colour form has many similarities to the west Atlantic form of H. picta.

I referred to Tom Thompson's paper in an earlier message [#622]. We can only hope that someone will consider the reproductive biology of the west Atlantic chromodorids to be worthy of study sometimes soon. Although some direct developers and lecithotrophic developers have restricted geographical distributions there are always examples which break the rules. As far as the local clustering you describe, I suspect this is in response to the presence of their preferred food sponge(s). Since veliger larvae settle and metamorphose on their food sponges, and the eggs of direct developers are usually laid on or near their food sponges, this sems to be the most likely cause of clustering, which is found in species of all development types.

Which brings me to the close-up I have included alongside. I am intersted in accumulating more data on the feeding specificity of the chromodorids so I always look carefully at photos for signs of potential food sponges. Most species of Hypselodoris feed on dysideid sponges. I am not sure if their is a ravaged dysideid colony in your photo or not. If you can see more in the original photo or have another photo which shows signs of such a sponge I would very much like a higher resolution scan to add to the Forum as a possibe feeding record.

Best wishes,
Bill Rudman

Dear Daniel,
Thanks very much. The egg ribbon, looks like it was laid on an aquarium air stone, which I have found to be quite a favourite place for nudibranchs to lay their eggs. I have added an inset of a magnified section of the ribbon to show the spiral string of eggs within the egg coil. The relatively large eggs are typical of a species with non-feeding lecithotrophic larvae. I have also used the photos of the adults at the top of the page. It's nice to be able to put a picture with such an interesting animal.
Best wishes,
Bill Rudman.

I have just noticed that Tom Thompson (1977) when discussing the limited distribution of Hypselodoris zebra says "it can be forecast that H.zebra will prove to have direct, non-pelagic development".

Austin's observations suggest that although its development is not direct, it is not very pelagic either, with non-feeding larvae quickly settling from the plankton.
Bill Rudman.

Reference: Thompson, T.E. (1977). The taxonomic status of two Bermudan Opisthobranchs. Journal of Molluscan Studies, 43: 218-222.

Dear Austin,
Thanks again for the photos. First your question about larval shells. Gastropod larval shells have essentially the same makeup as adult shells, but the are normally smooth and unsculptured. There is an outer proteinaceous layer of a chitin-like substance called conchiolin and an inner layer of calcium carbonate. One very distinctive difference between opisthobranch larval shells and "prosobranch" larval shells is that in opisthobranchs the shell coils sinistrally not dextrally. To explain what that means - if you hold a snail shell, spire pointing up and the aperture facing you, the aperture will normally be on the right hand side (dextral coiling). In opisthobranch larvae the shell aperture is on the left hand side. This means that when the animal metamorphoses, the shell has to change its direction of coiling from sinistral to dextral. The larval shell (protoconch) sits very awkwardly on top of the adult shell and is described as "heterostrophic". All "heterobranch" gastropods (opisthobranchs, pulmonates, etc) have heterostrophic protoconchs.

One other distinction between opisthobranch and "prosobranch" larvae is that opisthobranchs only have one larval kidney rather than the pair found in "prosobranchs". Even though it is called a kidney I think its function is not really understood.

Cilia, like those you can see around the edge of the foot, also occur all over the sole of the foot, and are for locomotion. The much larger cilia on the velum, occur in a large band at the edge of the velar lobes and are for swimming. In feeding veligers there are also fields of cilia on the face of the velar lobes which direct feeding currents to the mouth.

I think the large golden-brown globules present in all the photos are lipid-filled globules, most probably the remnants of the food stores present in the yolk.
Best wishes,
Bill Rudman.

Dear Austin,
What great photos! It was certainly worthwhile you taking up my idea of seeing if you could get the eggs to develop. Your photos show that Hypselodoris zebra has lecithotrophic larvae. Lecithotrophic larvae are relatively short-lived non-feeding swimming veligers which metamorphose into crawling juveniles after a period in the plankton. In some cases the lecithotrophic veliger can spend only a few minutes or hours before settling, in other species they last for a few days before settling. Have you any idea how long the veligers spent swimming before settling?

Your photos show (bottom left) a veliger which apparently has cast its shell and is about to settle down to benthic living. The black-edged lobes you can see are the reduced lobes of the velum - which with a band of beating cilia along the edge, are the veliger's swimming organ. In the photo (bottom right) of a metamorphosed juvenile, I have labelled some of the organs. I have never seen larvae with the brightly coloured pigmentation these ones do. The bluish purple region seems to include the buccal bulb and the nerve ganglia which cluster around the oesophagus just behind the buccal bulb and form its "brain".

The network of "spicules" form a structural network in the mantle tissue which is maintained in many dorid adults but is lost in most chromodorids. You have caught the larvae at such an early stage in their development that there does not seem to be any sign of rhinophore buds, and the larval kidney is still present. The otocysts are balance organs.

I am interested in the purple colouration. Did these animals have access to the sponge, Dysidea, on which the adults feed? If they did not, it suggests they carry pigment through from the egg - an interesting thought.

Thanks again Austin for sharing this interesting observation with us. It only goes to show that there are lots of valuable observations that can be made quite easily. One of the aims of the Forum is to publish such information. To me, and I presume to other researchers, such observations help to fill the many gaps in our knowledge. In themselves such observations usually are never published because they are too insignificant for a journal editor to bother with, or not "rigorous" enough for a scientific reviewer. To me they are all important pieces in a puzzle and I am happy to share them via the Forum.

Best wishes,
Bill Rudman.

Dear Austin,
Sorry to hear you were affected by "Mitch". I don't think I can really help with advice on possible research places in London. There are certainly no nudibranch workers there. John Taylor at the Natural History Museum might be able to give you advice.

Good luck with the egg raising and please keep us in mind if you find or photograph anything interesting.

Best wishes,
Bill Rudman

I think the "little purple nodules beneath the side flaps of tissue" you describe are mantle glands, which are characteristic of chromodorids. Each genus has a different arrangement of these glands. Have a look at the photosof Chromodoris woodwardae and Mexichromis macropus.

As luck would have it I have just discovered a student review The Sequestering of Secondary Compounds from Sponges by Nudibranchs by Tim Judd, Colorado State University ,which has been recently posted. He refers to a fairly recent study (Grode, S. H., J. H. Cardellina II. 1984) on H. zebra and food sponge chemicals.

You ask what you can do with six specimens. I presume you mean while they are still alive? It seems they feed on the sponge Dysidea so food choice experiments would seem a bit of a waste of time. What we really need is some good behavioural experiments to show that fish find them distasteful, and associate the bad taste with particular colour patterns. What you need on hand is a good behavioural scientist who can help you set up a proper experimental regime.

Going from the sublime to the ridiculous. I am not sure whether Hypselodoris zebra has planktotrophic larvae, lecithotrophic larvae or direct development.
Perhaps if you have access to clean sea water you could keep some egg-masses alive and see whether the young hatch as veliger larvae or as crawling young. Without the proper equipment actually measuring egg and embryo diameter to get some idea of development type may be too difficult.

What would be nice, and this goes for many species is to get a better idea of the range of colour variation is found within a population. If you can find more specimens and a range of size, it would be useful to record the colour patterns, and which parts of the pattern seem to be constant in all specimens etc.

The last part of your question about Rudman 1984. That is the chromodorid generic review paper in which I describe the the mantle glands.

References: Grode, S. H., J. H. Cardellina II. 1984. Sesquiterpenes from the sponge Dysidea etheria and the nudibranch Hypselodoris zebra. Journal of Natural Products 47(1):76-83.

Rudman,W.B.,1984. The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society, 81: 115-273.

Best wishes.... Bill Rudman