sea hares

  Bursatella leachi
De Blainville, 1817

Relevant Synonyms
Bursatella savignana Aouduin, 1826
Notarchus laciniatus Rüppell and Leuckart, 1828
Aclesia freeri Griffin, 1912
Bursatella leachii leachii [Palermo]
Bursatella leachii savignyana [Palermo]


 photo : L. Mizzan    

Slug like mollusc covered all over with simple and compound villi (papillae) of unequal size, giving it a ragged appearance. Head short and broad, with many branched median villi. Oral tentacles broad and projecting laterally. Foot broad, with a short acute tail. Parapodia short, not very mobile, their edges recurved and fused posteriorly high up, bearing a row of simple villi. A large arcuate ctenidium usually protudes through the dorsal slit.

color : dull brown or greenish brown, with reticulate markins, black spots and clear, brighter green areas, each with a peacok-blue ocellus (sometimes absent). Inner edges of the parapodia, mantle cavity and pedal sole paler.

common size : usually from 50 to 100 mm, up to 150 mm.

Eales and Engel (1935) reviewed the genus Bursatella and considered that there was a single species world-wide, B. leachii, which for convenience they divided into several geographical subspecies. Here we do not recognize this sub-division and treat the Mediterranean subspecies B. leachii leachii and B. leachii savignyana as synonyms.

The population numbers of this species fluctuate sporadically. Thousands of individuals can be present in a small area of a lagoon, in very dense aggregations, but may be entirely absent a few weeks later. Individuals seem to form a chain when copulation occurs (mainly in the late summer and autumn). Each specimen acts as a male (sperm donor) to the one in front, and as a female (sperm recipient) to the one behind. The egg masses consist of a tangled string, yellow-orange in color, adhered to the substratum. Each egg capsule within the jelly matrix of the string encloses from two to 20 embryos. The planktotrophic veligers hatch 7-8 days after ovoposition (at 25 °C) and they can delay the metamorphosis up to 2-3 month, until an adequate substratum for settlement is found. This extended time of the larvae in the plankton confers a high dispersal ability to the species. From gut contents, Bursatella leachi seems to be a deposit feeder with grazing habits (Russo, 1987).

habitat : in the Mediterranean usually found in soft bottoms covered by Caulerpa prolifera or by Cymodocea nodosa and Zostera noltii.

1st Mediterranean record
Palestine, 1940 [no collecting date].

Worldwide: circumtropical. Mediterranean: recorded first from Palestine (O'Donoghue and White, 1940); successively recorded in Turkey (Swennen, 1961); Malta (Bebbington, 1970); Israel (Eales, 1970); Sicily (Piani, 1980); Tunisia (several records from the Gulf of Gabès since 1982, Enzenross and Enzenross, 2001); Italy (Fasulo et al., 1984 as B. leachii and B. l. savignyana); Slovenia (Jaklin and Vio, 1989); Greece (Koutsoubas, 1992); Lebanon (collected by G. Bitar and H. Zibrowius, identification confirmed by J. Templado); Sardinia (collected by A. Olita, identification confirmed by J. Templado).

Very common from the eastern Levantine Sea to the Italian coasts; in the western Basin, only known from an area between Sicily, Naples and Sardinia.

speculated reasons for success :

Either by ships from the tropical Atlantic or via the Suez Canal.



  • Eales N.B., 1970. On the migration of Tectibranch molluscs from the Red Sea to the Eastern Mediterranean. Proceedings of the Malacological Society of London, 39: 217-220.
  • O'Donoghue C.H. and White K.M., 1940. A collection of marine molluscs, mainly opisthobranchs, from Palestina. Proceedings of the Malacological Society of London, 24: 92-96.
  • Russo G.F., 1987. Segnalazione di Bursatella leachi De Blainville, 1817 (Mollusca, Opisthobranchia, Aplysiomorpha) per le acque dell'isola d'Ischia e considerazioni sull'ecologia della specie. Bollettino della societa Naturalisti in Napoli, 94: 243-253, fig. 2, tav. 1.



Last update : December 2003

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