Bosellia mimetica
Trinchese, 1890

Superfamily: ELYSIOIDEA
Family: Elysiidae


Mediterranean, Atlantic coast of Spain. Also Caribbean and Atlantic coast of South America to Brazil.


L'Escala, Spain, 5m deep, September, 2000. <1cm long. Photo: Daco

Small (less than 8mm) sacoglossan, with a rounded and flattened body. Its mottled green colour matches the colour of the alga Halimeda tuna on which it lives and feeds. Its origins are unclear but it could be best described as an elysiid in which the parapodia are permanently opened. Thompson & Jacklin (1988) report finding it feeding on both Udotea petiolata and Halimeda tuna.

Compare with Elysiella pusilla from the Indo-West Pacific, another sacoglossan adapted for feeding and living on Halimeda.

• Marcus, Ev, (1973) On the genus Bosellia. Bull. Mar. Sci., 23(4): 811-823.
• Marcus, Ev. (1978) On a new species of Bosellia. Boletim de Zoologia da Universidade de Sao Paulo, 3: 1-6.
• Marin, A. & Ros, J.D. (1988) The Sacoglossa (Mollusca, Opisthobranchia) of the South East Iberian peninsula. A Catalogue of species and presence of algal chloroplasts in them. Iberus, 8(1): 25-49.
• Marin, A. & Ros, J.D. (1989): The chloroplast-animal association in four Iberian Sacoglossan Opisthobranchs: Elysia timida, Elysia translucens, Thuridilla hopei and Bosellia mimetica. Scientia Marina, 53(2-3): 429-440.
• Thompson, T.E, & Jaklin, A. (1988) Eastern Mediterranean opisthobranchia: Elysiidae (Sacoglossa = Ascoglossa). J. Moll. Stud., 54: 59-69.
• Trinchese, S. (1890) Descrizione del nuovo genere Bosellia. Memorie della Regio Accademia delle Scienze dell'Instituto di Bologna, 5: 773-778. figs. 1-12.

Authorship details
Rudman, W.B., 2000 (October 2) Bosellia mimetica Trinchese, 1890. [In] Sea Slug Forum. Australian Museum, Sydney. Available from

Related messages

Re: Two colors for Bosellia mimetica

March 26, 2008
From: Kathe R. Jensen

Concerning message #21045:

Dear Bill & Miquel,

When Bosellia mimetica feeds on Halimeda, it usually forms a white zig-zag trail on the Halimeda surface. The almost complete white surface on these pictures probably means that the animals have been feeding for a long time on the same spot. However, it may also indicate that Halimeda has "spawned" (released zoospores or gametes). Usually this involves terminal segments of Halimeda, and it looks like all contents of surface utricles leave the alga. Small clumps of very dark green material are seen towards the tip of these segments. This process often attracts sacoglossans, so finding 3 specimens of Bosellia close together could indicate this - though the brown specimen looks like it has not fed for a while.


Jensen, K.R., 2008 (Mar 26) Re: Two colors for Bosellia mimetica. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Kathe,

Bill Rudman

Two colors for Bosellia mimetica

March 25, 2008
From: Miquel Pontes

Dear Bill,

We found three Bosellia mimetica specimens in our last dive. One of them was curious because it was not colored green as they are normally found here, but instead it was colored brown.

I could not found color variability documented in the bibliography for this species, despite I have seen in the Forum that these variations do exist.

These animals were found on Halimeda tuna, but curiously these algae were almost white in color and showing their calcified structure. Maybe the Halimeda algae were dying because of some other reasons, but could the Bosellias be the reason for the "bleaching" ?

Locality: Platja de Caials, Cadaqués, Costa Brava, 15 metres, Spain, Mediterranean Sea, 27 october 2007, Precoraligen rocky bottom. Length: 6-7 mm.. Photographer: Miquel Pontes.

Best regards,
Miquel Pontes

Pontes, M., 2008 (Mar 25) Two colors for Bosellia mimetica. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Miquel,

It is certainly interesting to find a brown colour form in the Mediterranean. It certainly accords with Colin Redfern's find of similarly coloured animals in the Caribbean. [see message #6121]

Concerning white patches on the Halimeda - I had always presumed they were from the activities of the sacoglossans, and as you can see in the close-up, the white regions are often patches on the green background, much like the scrape marks left by a grazing limpet. However these animals don't feed by scraping or grazing, they pierce a hole through the skin and suck out the cell contents. Perhaps in this example each patch represents an area of the plant that has had its cell contents sucked out.

Best wishes,
Bill Rudman

Rudman, W.B., 2008 (Mar 25). Comment on Two colors for Bosellia mimetica by Miquel Pontes. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Bosellia mimetica from French Mediterranean

July 31, 2002
From: Marina Poddubetskaia

Dear Bill,
There is a photo of Bosellia mimetica on the alga Halimeda tuna, and a close-up of the animal and its egg-ribbon.

Date: July 02, 2002
Location: Cerbere, France [Mediterranean coast]
Site: Cap Negre
Size: animal = 7-8mm / egg-ribbon = 3mm
Photos: Marina Poddubetskaia - Nembro website

Best wishes,

Poddubetskaia, M., 2002 (Jul 31) Bosellia mimetica from French Mediterranean. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Marina,
It certainly looks similar to its Indo-West Pacific counterpart, Elysiella pusilla, which also lives and feeds on a species of Halimeda. I don't recall having seen an egg ribbon of E. pusilla however.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Jul 31). Comment on Bosellia mimetica from French Mediterranean by Marina Poddubetskaia. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Bosellia mimetica in the Bahamas

February 3, 2002
From: Colin Redfern

Dear Bill,
I see that Bosellia mimetica is already on your Species List, but I thought you might like to have photos of two additional specimens. These are both from Abaco, Bahamas, where B. mimetica is occasionally found close to shore on Halimeda opuntia or on small rocks. As shown by these photos, the animal's shape can change considerably when in forward motion, and the shade of green is quite variable. The photographed 9 mm animal is the largest I've seen, but Clark (1984) recorded a 15 mm specimen from Bermuda.

UPPER: Two photos of a 9 mm specimen. On the underside of a rock in 0.3 m, shoreline 1 mile SE of Cooperstown, Abaco, Bahamas. June 12, 1995.
LOWER: Three photos of a 5 mm specimen. On Halimeda opuntia in 0.6 m at entrance to lagoon on No Name Cay, Abaco, Bahamas. June 30, 1995.

• Clark, K. B. 1984. New records and synonymies of Bermuda opisthobranchs (Gastropoda). The Nautilus, 98(2):85-97.

Best wishes,

Redfern, C., 2002 (Feb 3) Bosellia mimetica in the Bahamas. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Colin,
Thanks for the further information. I remember spending many hours searching for Bosellia in the Indo-Pacific, because as I mentiond in an earlier message Eveline Marcus was very keen to see specimens from the Indo-Pacific - but they don't seem to exist here.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Feb 3). Comment on Bosellia mimetica in the Bahamas by Colin Redfern. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Bosellia mimetica from Spain

October 5, 2000
From: Daco

I would like to send you an image of Bosellia mimetica.

size: <1cm
depth: 5 m
date: 16.9.2000
country: Spain
village: L'Escala
divesite: Illa Mateua; night dive


Daco, 2000 (Oct 5) Bosellia mimetica from Spain. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Daco,
Thanks very much for the photo. In general shape, Bosellia looks quite like Elysiella pusilla which also feeds on species of Halimeda. They both have a very flattened body, probably as a form of camouflage. The late Eveline Marcus told me she considered Bosellia to be her favourite genus. I suspect this was because Bosellia looks quite like the outline of a cat, with which she often used to decorate her letters. She was very disappointed that I could never send her species of Bosellia from the Indo-West Pacific, but apart from unverified reports from South Africa and the Red Sea, I don't think any species of Bosellia has been found outside the Atlantic.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Oct 5). Comment on Bosellia mimetica from Spain by Daco. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from