Costasiella from Hawaii

November 16, 2003
From: Dan Barshis

Is this an aeolid [Berghia or Spurilla perhaps?

It was collected on the south shore of Oahu, Hawaii, at nearshore depths (<1m). The area was typically a sandy, mud bottom. The specimen is approximately 4-5mm long. We found it in our aquarium with our other collections from the site approximately 1 week later. We were actively collecting Plakobranchus ocellatus and some Chelidonura spp. along with some algae. As seen in the photo the orangish-golden color has a metallic, sparkle. The green color could be attributed to symbiotic algae in the cerata. Any information regarding this species would be much appreciated as we were unable to determine its identity from the guide on this website.
Thanks for the help,
Dan Barshis

Barshis, D., 2003 (Nov 16) Costasiella from Hawaii. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Note added 17 Nov 2003: this is Costasiella sp. 1. See Clay Carlson's message.

Dear Dan,
Although it certainly looks like an aeolid nudibranch it is in fact a sacoglossan that looks like an aeolid. Sacoglossans are all herbivores so the green aggregations in the cerata are likely to be clusters of chloroplasts they have obtained from their algal food. I am not sure if species of Costasiella retain the chloroplasts alive. The genus Costasiella is easily identified by the pair of eyes situated close together in the dorsal midline. No other opisthobranch has eyes like this, so even without knowing the differences between sacoglossans and aeolids, it is possible to confidently identify these animals to a genus. However we still have a lot of problems identifying individual species so unless Kathe Jensen can give us a species name I will call this Costasiella sp. 4
Best wishes
Bill Rudman

Rudman, W.B., 2003 (Nov 16). Comment on Costasiella from Hawaii by Dan Barshis. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Costasiella sp. 1.

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