Dear Jeffrey,

I suspect this is the wrong time of year for A. bullata.

If anyone can help please contact Jeffrey directly.

Best wishes,
Bill Rudman

Dear Clare & Dick,

Thanks for the information. Like their relatives, the sea hares, when Akera is present it usually occurs in large numbers. Unfortunately it can never be guarateed to be present when 'needed'. So if there is anyone in southern England who would like a specimen or two for DNA this might be a good time for a visit to Eastbourne.

Best wishes,
Bill Rudman

Thanks Barry,
Bill Rudman

Dear Grey,
Your video has caused a flurry of correspondence. I have had 6 people alert me to it from various parts of the world and have included a frame from the video with your message. It is definitely Akera bullata.

Best wishes,
Bill Rudman

Dear Sylvie,
I have split you message in two so we have a better look at this photo of two animals mating.

As I discussed before, Akera, although a primitive sea hare, has many features in common with the cephalaspidean bubble shells, with a large external shell and a hermaphrodite reproductive system in which the female opening is at the opening of the mantle cavity on the right side,  within the shell opening, and the penis is at the front of the body on the right of the head. As I described in your last message [#20044], there is an external groove to carry the sperm from the female genital opening forward to the penis. When mating takes place these animals do not sit right side to right side like nudibranchs, but the animal acting as the male must have its head up on the right side of its partner so the penis can be in contact with the female genital opening. That is what we can see in the close-up photo alongside - the head of the animal in the foreground is acting as the male and has the front of its head squeezed in between the right parapodia and the shell of the animal behind which is acting as the female. 

Best wishes,
Bill Rudman

Dear Sylvie,
Thanks for the wonderful photos and information on this mysterious species. I guess the short period when it is seen is one of the reasons few people have studied it. Your description of it apparently arriving fully grown, breeding and then dying could be a description of what we know about many sea hares [see mass mortality page ]

Your mention of the Hancocks Organ reinforces the idea that many have had that Akera was actually a cephalaspidean 'bubble-shell' right up to Thompson in (1976). I remember discussing this with him but was unable to convince him that Akera was a proto-sea hare rather than a strange cephalaspidean. The Hancock's Organ is essentially a chemosdensoty organ found in cephalaspideans and consists of a sensory pad on each side of the head. I must make a point in preparing a page showing this organ. Umbraculum has a similar organ, also called a Hancock's Organ [see 3967], but its difficult to know if they are tthe same structure or not.

As I have said before, we don't know much about Akera, but one of the earliest studies (Guiart, 1901) is often ignored although it is extremely thorough and valuable. Guiart clearly realised the close relationship between Akera and the sea hares, In his anatomical account he describes a Hancock's Organ on each side of the head, in the groove between the head shiled and the foot. In your photo alongside it is the greyish brown band. It certainly is in the same place as in cephalaspideans and Guiart does describe some nerve branching to it, but I think we will need further work to see if it a chemosensory structure. Guiart calls the ear-like structures behind each eye as 'rudimentary rhinophores' and I would agree that they are the fore-runners of the sea hare rhinophore [see aplysiid head page]. In the aplysiids it is the rhinophores which have a chemosensory function, so it is possible there are chemosensory receptors on the ear-like flaps in Akera. If so, it would suggest the bands we are calling 'Hancocks Organs' in Akera are not these organs at all.

The other thing you can see in the close-up of the head is a whitish groove along the top of greyish band we are calling the Hancocks Organ. This is the sperm groove which carries the sperm from the female genital opening in the mantle cavity [which is back in the shell opening] forward to the penis which opens on the right side of the head. A similar groove can be seen in sea hares. I will talk more about mating in Akera in a separate message [#20050 ].

Concerning feeding, it is possible it does not normally feed on red macroalgae. I should have said in reponse to Helen Marshall's message [#19999] that there are a few exceptions to the red algae rule and they are Bursatella leachii and Stylocheilus striatus which feed on layers of 'blue-green algae' or cyanobacteria forming a layer of the sandy mud surfaces. This 'food' contains the chemicals needed to produce their red ink. Perhaps Akera also feeds on this layer. In my comments on Helen Marshall's message I said that Thompson & Seaward did not observe what Akera fed on, but I missed a couple of sentences where they say that in summer it fed on rafts of the green alga Enteromorpha and during the remainder of the year the brown gritty faeces suggested they fed directly on the sediment. [I have corrected my earlier comment].

• Guiart, J. (1901) Contribution à l'étude des Gastéropodes opisthobranches et en particulier des céphalaspides. Mémoires de la Société Zoologique de France 14: 1-219, pls. 1-7.

Thanks so much for these interesting photos,
Best wishes,
Bill Rudman

Dear Helen,
Thanks for these very welcome photos. Apart from D.P.Wilson's photos in Thompson (1976) of swimming animals I don't think I have seen photos of them crawling like this. Although externally they look nothing like a sea hare, their anatomy [see Fact Sheet] shows their close relationship. Their large external, thinly calcified shell, like those in many cephalasideans and sacoglossans, suggests that all these opisthobranch groups arose from ancestors in which the calcified external shell of a snail was gradually lost as they evolved into 'slugs'.

 I am very interested to hear that it will eat the red alga Chondrus as I can find no information on its diet. Thompson & Seaward (1989) observed that in summer Akera fed on rafts of the green alga Enteromorpha and during the remainder of the year the brown gritty faeces suggested they fed directly on the sediment.  Certainly aplysiids tend to prefer red algae and are facultatively 'de-inked' if they have no red algae in their diet. I would be interested to hear of any other information you have on its diet, because we have no information on the Indo-West Pacific species A. soluta.

• Thompson, T. E. (1976) Biology of opisthobranch molluscs. London, Ray Society no. 151.  1-207.

Best wishes,
Bill Rudman

Thanks Andrej,
Best wishes,
Bill Rudman

Dear Ian,
Good luck. If you get a chance, it would be nice to get some photos of it crawling as well.

Best wishes,
Bill Rudman

Dear Ian,
This is an interesting observation which has rarely been reported. The animal is Akera bullata, which is a very primitive Sea Hare rather than a nudibranch [see Akeroidea Fact Sheet]. They have a bubble-shaped external shell and although they spend most of their time crawling or burrowing in fine mud on sheltered shores and bays, they can at time form swimming swarms, often in quite large numbers. Some say swarming is involved with breeding, while others say it is the juveniles that usually swarm, but basically this 'swarming - swimming' behaviour has not been studied in detail and only reported in the scientific literature 3 or 4 times, so it is not possible to say anything very sensible about it.  The drawing alongside is from Morton & Holme (1955) who report spawning and swimming from April-July in the English Channel coast. Theanimals swim rather awkwardly with their heavy (shelled) end hanging down, more like large heavy flying beetles, than bees. I haven't any photos of living Akera bullata, but it is quite similar in shape to Akera soluta from the Pacific.

• Morton, J. E. and Holme, N. A. (1955) The occurrence at Plymouth of the marine opisthobranch Akera bullata, with notes on its habits and relationships. Journal of the Marine Biological Association, United Kingdom 34: 101-112

Best wishes,
Bill Rudman