Tuesday, 6 March 2012

The Spanish dancer (Hexabranchus sanguineus)

The Spanish dancer (Hexabranchus sanguineus) - Photo by/ Ahmed F.Gad
The Spanish dancer (Hexabranchus sanguineus) is typically red and it is one of the largest nudibranchs - many over 40cm in length.These brightly colored, undulating swimmers are found throughout the tropical Indo-Pacific and Red Sea.  They were given the name Spanish dancer because their swimming movement (often referred to as dancing) resembles the movement of a Spanish flamenco dancer's dress. The animal whirls, spins and undulates - its unfurled parapodia (the wide edges of the mantle) creating the ruffled-dress look that propels it though the water.

When the Spanish dancer is not dancing, it crawls.  It's parapodia are tightly curled around the edges of the mantle, and it moves quite slowly.
As an unusual member of the Superfamily Eudoridoideahe, the feather-like or soft, leaf-like gills on the mantle are exposed and do not have a pouch in which they can retract.  In fact, each gill is inserted separately into the body wall.

Unlike other nudibranchs that move by crawling, the Spanish Dancer gets its name from its ability to swim, in an undulating motion, using its red “skirt” which waves about and unfurls as it propels itself through the water. The motion looks very similar to an exotic flamboyant flamenco dancer.  While it mostly prefers to crawl along the reef like other nudies, the dancer will unfurl it “skirt” and propel itself into a swim usually when it feels threatened.

Most nudibrachs lay eggs in a ribbon shaped rose pattern on rocks and coral which are white or blue in color, however you can instantly recognize the eggs that belong to a Spanish dancer’s which will look like a red rose, lodged on a rocky outcrop. The eggs of this creature are crimson red and highly toxic, containing a greater concentration of poison than the adult of the species.

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