Re: Costasiella sp. 1 from Hawaii

February 7, 2002
From: Kathe R. Jensen

Dear Bill,
Every time I see messages about species of Indo-Pacific Costasiella on the Forum I get a bad conscience. I have 4 or 5 species of Costasiella from Singapore, which I was supposed to have described with Jon Sigurdsson, and I have 2 species from Guam and 2 from Phuket, one of which may be the same, and also one from India, which may be identical to one of the Singaporean species. The reason my Costasiella - paper never even got started is that this awful paper by Ichikawa appeared. In this paper she describes 6 species of Costasiella based on photos and serial sections. There are so many characters not mentioned in these descriptions that it is impossible to compare these species with others. I had hoped to have time in Vienna to look at the holotype sections, but I had to go back to Thailand for teaching. So Costasiella remains one of my bad consciences. But it is nice to see that apparently one species has a wide distribution. Judging from the pictures in Ichikawa's paper it is not one of her species.

Reference: Ichikawa, M. 1993. Saccoglossa (Opisthobranchia) from the Ryukyu Islands. : 119-139.


Jensen, K.R., 2002 (Feb 7) Re: Costasiella sp. 1 from Hawaii. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Kathe,
I mentioned the Ichikawa paper in the first message that was sent to the Forum on this species. It seems many species of Costasiella have quite a distinctive colour pattern so perhaps not all is lost. I guess the problem is that without using anatomical characters as well it is difficult to know whether Ichikawa's species are colour varieties or distinct species. For example the black 'collar' or 'spectacles' in Costasiella sp. 1 seems very distinctive but it is possible that Ichikawa's Costasiella iridophora is based on a specimen without these black markings.

I guess the only way forward is to describe your species as fully as possible and if necessary, name them as new species. If they are later shown to be synonyms of one of Ichikawa's species that is a small price to pay for having your information available to us all.
Bill Rudman

Rudman, W.B., 2002 (Feb 7). Comment on Re: Costasiella sp. 1 from Hawaii by Kathe R. Jensen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Costasiella sp. 1.

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