Sedna, Glossodoris sedna

Sedna, Glossodoris sedna.  Nudibranch collected from under tidal pool rocks in the low surge zone in the Greater Los Cabos area, Baja California Sur, January 2016. Length: 2.5 cm 1.0 inch).

Sedna, Glossodoris sedna.  Underwater photograph taken in coastal waters of the greater Los Cabos area, Baja California Sur, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.

Sedna, Glossodoris sedna.  Underwater photographs taken in Zihuantanejo Bay, Guerrero, December 2019. Photographs and identification courtesy of Maude Jette, Dive Zihuantanejo, www.Divezihuatanejo.com.

Phylogeny:   The Sedna, Chromolaichma sedna (Ev. Marcus & Er. Marcus, 1967), is a member of the Chromodorididae family of Nudibranchs. The genus Chromolaichma is one of sixteen genera in this family, and there are four species in this genus. Sednas are also called the Red-tipped Sea Goddess.  This species is also called Sedna in Mexico. The name Sedna comes from the Inuit goddess who created the sea creatures of the Arctic. The name Sedna is shared by a planetoid, located 8 billion miles from Earth, where the temperature never exceeds minus 400 degrees Fahrenheit! It is the most distant object in our solar system.

Morphology:  Sednas are soft-bodied gastropods that lose their shell during their larval phase. They have a thick mantle on their back (dorsal surface) that extends over the foot. Their gills are retractable, and consist of feathery plumes that encircle the anus. They have rhinophores (horn-like projections) on their heads. Rhinophores are chemosensory organs help them to locate food and potential mates. They lack complex eyes, but have photoreceptors that sense light and dark. Sednas have an elongate oval outline, with a long, tapering tail. They are white in color. The margins of the mantle and tail are red and yellow. The tips of the rhinophores and gills are dark red. The gills are usually moving, to increase oxygenation. The mantle is often frilly in appearance. Sednas reach a maximum of 6.3 cm (2.5 inches) in length.

Habitat and Distribution:  Sednas are found on and under rocks and sponges intertidally and to depths up to 20 m (66 feet). They are a tropical Eastern Pacific species and are found in Mexican waters of the Pacific Ocean throughout the Sea of Cortez and south along the mainland coast to Guatemala. They are absent from the west coast of the Baja Peninsula. Sednas have been introduced to, and are now established in, the tropical Western Atlantic. They may soon be arriving along Mexico’s east coast.

Diet:  Sednas are spongivores, which feed exclusively on spiculated demosponges. They are known to feed on at least seventeen different species of demosponges.

Predators: Sednas are a poorly studied and understood species. It is known that they incorporate toxins from their prey to produce chemical compounds that make them dis-tasteful or poisonous. There is no documentation of predators for this species. Other species in this family are usually prey for other nudibranch species.

Reproduction:  Sednas are simultaneous hermaphrodites. They reproduce sexually by hypodermic insemination. This occurs when both mating partners dart their penis toward each other to induce one to act as a male and the other as the female. The victorious one to penetrate the body wall is the dominant male. The eggs are laid as a mass on the bottom stratum. The eggs hatch into veliger larva and later metamorphose into adults.

Ecosystem Interactions:  Sednas are a poorly studied and understood species. There are no documented commensal, parasitic or symbiotic relationships between Sednas and other species.

Human Interactions:  Sednas have been introduced to the tropical Western Atlantic, where they are considered to be an invasive species. It is thought that they were transported in ship ballast water. It is unknown how much impact they have had or will have on the Atlantic/Caribbean ecosystems. Otherwise, have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms: Casella sedna, Chromodoris fayae, Chromodoris sedna, Doriprismatica sedna, and Glossodoris sedna.