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Gregory R. Mann, Ph.D. {ret.}

Nudibranch

“Acanthodoris hudsoni”

The word Nudibranch pronounced “nooda-brank” which means “naked gills” and consist of soft-bodied Sea Slugs who are members of the class Gastropoda in the phylum Mollusca. The majority of the colorful opisthobranchs that are seen belong to the suborder Nudibranchia. Nudibranchs can be found anywhere from the depths of the ocean, to tidal pools, to coral reefs but are most diverse in tropical waters. Nudibranchs have an irregular shape that can be thick or flattened and long or short and can range anywhere from 0.635 centimeters to 60.96 centimeters. The average lifespan of a Nudibranch can vary anywhere from weeks to 1 year, based on the abundance of food available to them. Nudibranchs are carnivores and use their radula, a band of curved teeth, to scrape or tear food particles. They feed on species such as hydroids, sea anemones, corals, sponges & fish eggs. Each species of Nudibranch usually specializes on one specific sessile animal on which to feed. Nudibranchs move or “crawl” by ciliary action or the muscular action of its foot, a flat and broad muscle that clings to rocks, corals, sponges and other surfaces.

Although separated into four different groups, the two most common groups of Nudibranchs are the aeolidida (aeolids) and the doridoidea (dorids). Doridoidea is the largest group of Nudibranchs and is comprised of many different variations of body types. Aeolidida are the second largest subgroup of Nudibranchs and show a more consistent elongated shape. Nudibranchs have both male and female sex organs, making them hermaphrodites. Although hermaphroditic, self-fertilization does not occur. Only when the reproductive pores of two Nudibranchs line up neck to neck, can fertilization ensue. Nudibranchs have obtained different defenses in order to escape predation; chemical defenses are obtained from their prey by ingestion and are then incorporated into Nudibranch tissues. The bright colors & patterns of Nudibranchs serve as a warning signal to predators of their chemical defenses. Alternatively, the coloration of Nudibranchs could also be a camouflage mechanism, allowing them to blend in to various substrates. Some have developed poison that is injected as a defense which also includes human skin when handled.

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