October 13, 2000
From: Jeff Goddard
Here are photographs of three species of chromodorids not yet pictured in the Forum. I found the Glossodoris sedna and G. dalli in the shallow subtidal off Isla Luz, Bahia de Concepcion in the Sea of Cortez, and the Chromodoris norrisi in shallow water off Izla Danzante, also in the Sea of Cortez. All were found in February, 1992.
I have not studied any aspect of the biology of these species, but could not help but notice how actively G. sedna wiggled its gill plumes. This was striking to someone used to observing temperate water dorids. I assume this activity facilitates gas exchange in warmer waters. Is it common in shallow water, tropical chromodorids?
Goddard, J., 2000 (Oct 13) Three eastern Pacific chromodorids. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/3142
Thanks for the photos. I have moved the photos of Glossodoris sedna and Chromodoris norrisi to separate pages. Your question about wriggling gills is interesting. Many species of Glossodoris wriggle their gills as you have observed for G. sedna. I thought at first that it could be linked to physiology, but I was thinking more that in many of these species the body wall had become thick and muscular and so was less useful as a 'secondary gill'. This argument was hard to sustain when I realised how most species of Thorunna also wriggle their gills. There are also a few species of Noumea that do likewise. It is certainly a good character to note in the field, as it is not exactly obvious in preserved animals or photographs.
An interesting point about gills though is that in many species of Glossodoris the ends of the gill arch form an internal spiral, so greatly increasing the number of gills. I suspect that this is related to the thickening of the body wall.