Berthella medietas from New Zealand

September 7, 2005
From: Jeff Goddard

Hi Bill,
While in the Wellington area I found intertidally two specimens of Berthella that Richard Willan kindly identified from the accompanying images as B. medietas Burn 1962.

Locality: Tarakena Bay, Wellington, New Zealand. Intertidal. Length: 10 mm
21 August 2005. Rocky shore, low intertidal pool. Photographer: Jeff Goddard

One of the specimens was grazing on the sponge Oscarella sp., which was the most abundant sponge in the under-rock habitat I was searching in. This record, combined with the record of B. ocellata feeding on Plakina trilopha and Bernard Picton's report [message #5894] of B. plumula feeding on Oscarella in the British Isles, suggests that sponges of the family Plakinidae may be a common dietary component of species of Berthella. However, because Oscarella lacks skeletal elements, it would be missed in visual examinations of gut contents. With this in mind, I would like to make another attempt at determining the diet of B. californica from the NE Pacific Ocean. The diet of that species eluded me during my time in Oregon (the guts of the few specimens I examined never had anything recognizable in them), but I have since learned that one of the sponges I had found intertidally in Oregon is indeed an Oscarella.

Best wishes,

Goddard, J.H.R., 2005 (Sep 7) Berthella medietas from New Zealand. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Jeff,
Another valuable find - and another species to add to the Forum. We can also add Richard Willan's report (1984) of another New Zealand species, Berthella ornata, with it stomach full of the spicules of Plakina monolopha. As well as Picton's report of Berthella plumula feeding on Oscarella, there is also Delaloi & Tardy's study (1977) showing it fed only on Oscarella lobularis, excluding all other sponges it was tested with.

  • Delaloi, B. and Tardy, J. (1977) Regime alimentaire et ethologie predatrice de Berthella plumula (Montagu, 1803), mollusque opisthobranche. Haliotis, 6: 273-280. [for 1976].
  • Willan, R. C. (1984) A review of diets in the Notaspidea (Mollusca: Opisthobranchia). Journal of the malacological Society of Australia, 6: 125-142.

Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Sep 7). Comment on Berthella medietas from New Zealand by Jeff Goddard. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Berthella medietas