Hexabranchus sanguineus (Rüppell & Leuckart, 1828)

Hexabranchus sanguineus is a large, mostly red nudibranch. They tend to hide by day but will often come out of their holes at night to wander in the open. They are not commonly found in the Marshalls, but a few have been seen at Enewetak and Kwajalein Atolls. They have been found in lagoon and seaward reef habitats from the surface--one was found still alive, just washed in on the eastern seaward beach of Enewetak--to depths of more than 50 meters on the seaward reef slope.

The photo below shows the wavy oral tentacles that flank the mouth on the underside of the anterior end.

The individual below is the one that was washed in on the beach at Enewetak. When returned to the depths, it seemed to be fine and crawled away.

Hexabranchus sanguineus is one of the few nudibranchs with a well-known common name. It swims when disturbed, and it can flare out its normally rolled up margins to look like the flowing skirts of a dancer. Not surprisingly, it is known as the Spanish Dancer nudibranch. It swims by flexing its body up and down and paddling itself through the water.

This is by far the largest nudibranch found so far in the Marshalls. The individual below was one of four individuals observed one night (29 Sep 1989) on the leeward seaward reef slope at a depth of about 20 meters. They were not accurately measured, but by measuring them against camera gear it was obvious that each of the four exceeded 500mm in length. There were also several egg masses scattered about that night. In the 17 years since then, despite hundreds of dives in the same general area and under similar conditions, we have seen large Hexabranchus only a couple more times and never more than one at a time. You'd think something that large would not be able to hide that well.

Young specimens are very colorful, almost looking like a kind of chromodorid nudibranch.

At 8mm long, the individual directly below was one of the smallest we have found, beaten only by the following photo of a 6mm animal.

Created 15 December 2006
Updated 19 September 2008