Nudibranchs - Cinderella of the Salish Sea


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White tendrils are nerves and are connective tissue surrounding dozens or hundreds of single neuron fibers (axons) Brain is in two parts, but right side controls right side, left controls left

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Nudibranchs, the Cinderella of the Salish Sea Presentation for the SeaDoc Society October 12, 2011 By Karin Fletcher Miller

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Copper rockfish swimming away Ling cod swimming away…but what’s in the background? One of the joys of scuba diving is taking pictures of fish  One of the disappointments of scuba diving is taking pictures of fish tails 

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Red sponge nudibranch But there are some things that sit still – Nudibranchs! Yellow margin dorid

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What are nudibranchs?

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Land slugs

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Sea slugs or Nudibranchs = “naked gill”

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Basic land slug anatomy Basic sea slug anatomy Both are a subclass of gastropod molluscs (chitons, bivalves, univalves, octopus, squid) Sea slugs are adapted to a marine environment gills or cerata (instead of lungs) a reduced or non-existent shell , except in larval stage

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White –and-orange-tipped nudibranch heartbeat open circulatory system copper-based blood (hemocyanin) Double-click the image to start the video

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Aeolid anatomy Dorid anatomy

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About 3,000 known species worldwide About 86 species in the Salish Sea Dorid Aeolid Other Dendronotus Armina

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Dorid body type – non-branching digestive system Gills in the back No cerata, but can have toxin-filled glands around the mantle margin to deter predators Can have needle-like spines in their mantle called spicules to deter predators Often have dorsal bumps called papillae or tubercules

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Sandalwood dorid nudibranch with papillae

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Close-up of tubercules and spicules on a Fuzzy onchidoris

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Aeolid body type – branching digestive system Each blood-filled ceras has a duct of the digestive gland Can store stinging cells called nematocysts from the corals, hydroids, bryozoans or anemones they eat in the tips of their cerata for their own defense Red Flabellina

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Diamondback nudibranch Orange doto Dendronotus Orange-peel nudibranch Hooded nudibranch

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Neurologists study nudibranchs at the University of Washington’s Friday Harbor Laboratories on San Juan Island One study involved comparing how a neuron in the Pink tritonia and the same one in the Hooded nudibranch is used for different forms of movement Pink tritonia Hooded nudibranch

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LP & RP = Left and Right pedal ganglia control the foot and lateral body wall CG = Cerebral ganglia control the head PG = Pleural ganglia control the gut and dorsal body wall Photo of Tritonia diomedea brain courtesy of Dr. James Alan Murray, California State University East Bay Pink Tritonia brain

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Striped nudibranch Armina Golden dirona White-and-orange-tipped nudibranch Frosty-tipped nudibranch Armina with cereta have the anus on a papilla on the rear third of the right side

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Other marine gastropods related to nudibranchs Headshield slugs Spotted aglajid Sea hares Taylor’s sea hare Sap-sucking sea slugs Enteromorpha-eating sapsucker Side-gill marine slugs California berthella

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How big (or small) are they?

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Grains of rice Rustic aeolid nudibranch Some nudibranchs are small

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Pink Tritonia Pink Tritonia and fin Other nudibranchs are huge

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How do nudibranchs get around?

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White-and-orange-tipped nudibranch Double-click the image to start the video Giant nudibranch swimming Primarily crawl using cilia on the underside of their foot which beat and move it along the mucus secreted by its foot Able to crawl on the surface tension of water Some can swim – giant nudibranch, hooded nudibranch, pink tritonia

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How do nudibranchs eat?

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Nudibranchs, like all molluscs except bivalves, have a tongue-like chitonous toothed ribbon called a radula which they use to grasp, scrape or shred the sponges, corals, anemones, hydroids, bryozoans, tunicates, barnacles, algae, and sometimes other nudibranchs that they eat. These are the “teeth” of a coral-eating nudibranch.

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Another type of mollusc – a chiton - with a path that its radula made

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An Opalescent nudibranch is a voracious eater

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Nudibranch life cycle

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San Diego or Leopard dorid with egg ribbon Red sponge nudibranch pair with egg ribbon Have both male and female reproductive organs, generally not self-fertilizing Lay up to 2 million eggs at a time Can store sperm and lay eggs at a later time Lifespan – some less than a month, others up to one year

Slide 31 Eggs take 10-20 days to hatch Direct – eggs hatch as tiny nudibranchs Indirect – eggs hatch as free-swimming veligers with a shell that only settle and lose their shell when they have found a suitable food source Lecithotrophic – indirect but with a yolk that sustains veligers until they metomorphose

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White-lined dirona larva after hatching Notice the shell Photo by Cameron Hirtle Hirano, Y.J., 1999 (June 21) Flabellina amabilis Larval metamorphosis. [In] Sea Slug Forum. Australian Museum, Sydney. Available from Charming aeolid larval metamorphosis - Settling on food - Casting off shell - Dinner!

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What do nudibranchs eat?

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Hydroids Related to anemones; tentacles have stinging cells Individuals are connected to each other; food is shared throughout colony Embedded sea fir hydroid Pink-mouthed hydroid Hedgehog hydroid

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Hydroid close-up

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Bryozoans – “moss animals” More complex than hydroids and worms Tentacles have horseshoe-shaped cilia around mouth Encrusting bryozoans develop spicules in response to predation Spiral bryozoan Fluted bryozoan Kelp-encrusting bryozoan

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Sponges, anemones and sea pens Sponges contain toxins for defense Anemones and sea pens contain stinging cells to immobilize their prey Red sponge Tube-dwelling anemone Orange sea pen

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White-lined dirona before eating After a meal Nudibranchs are what they eat

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Nudibranch defense and coloration

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Bright color denotes a toxic or unpleasant taste (aposematic) Cryptic colors blend in with the environment – especially for some nocturnal species Opalescent nudibranch Red dendronotus

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Pink-mouthed hydroid and anemone Fernald’s aeolid on pink-mouthed hydroid

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Fernald’s aeolid close-up

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Hedgehog hydroid Pink cuthona in hedgehog hydroid

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Pink cuthona in the open

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Giant nudibranch Tube-dwelling anemone

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Giant nudibranch

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Red sponge Red sponge nudibranch

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Red sponge nudibranch is easier to see when it’s not on a red sponge

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A number of toxic chemicals have been isolated from nudibranchs but most are too toxic to be used on humans. More than 300 chemicals have been described from only a fraction of the total nudibranch species Cooper’s dorids change metabolites they eat into more toxic chemicals Monterey dorids have toxic chemicals in them that are not present in the food they eat Marine Opisthobranch Molluscs: Chemistry and Ecology in Sacoglossans and Dorids Neville Coleman’s World of Water

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How do aeolids ingest the stinging cells of cnidarians to use for their own defense? A hard cuticle covers the mouth (buccal cavity) and throat (esophagus) Stomach cells have spindles that form a physical barrier to nematocysts Nudibranch mucus can inhibit nematocyst firing Verrucose aeolid

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What eats nudibranchs?

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Decorator crab with nudibranch egg ribbon – caviar for crabs? Sea stars Mosshead warbonnet has been seen bending a nudibranch in half to eat it* *

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Maybe this Blackeye Goby had indigestion later, but he or she sure didn’t hesitate to try to swallow this clown dorid* *Thanks to Gene Coronetz for this info and to Talon for the photo

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Double-click image to start video Pink tritonia escaping from a sunflower seastar Video of Tritonia diomedea courtesy of Dr. James Alan Murray, California State University East Bay

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Looks like something tried to take a bite out of this nudibranch Its cereta will grow back in just a few days

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You don’t have to scuba dive to find nudibranchs

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Shaggy mouse nudibranch at low tide Monterey dorid on piling Giant nudibranch on a dock

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You could even discover new ones!

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Researchers at the California Academy of Sciences are studying the DNA of the Onchidoris family because coloration alone isn’t enough for positive ID

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Photograph courtesy Terry Gosliner, California Academy of Sciences June 28, 2011 - New Nudibranch The Philippines expedition discovered at least 50 new species of nudibranch, including this one in the Armina genus. The area surrounding Luzon is renowned for its nudibranch diversity, with more than 800 species known. This makes the discovery of 50 new species even more remarkable, Burke said— especially because expedition leader Gosliner, a nudibranch expert, has been diving around Luzon since 1992.

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Thank you! Questions?

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References Marine Life of the Pacific Northwest – Andy Lamb and Bernard P. Hanby Biology of Opisthobranch Molluscs – T. E. Thompson Eastern Pacific Nudibranchs – David W. Behrens and Alicia Hermosillo Nudibranch Behavior – David W. Behrens Sea Slug Forum ( Nudi Pixel ( The Slug Site ( Nudibranch food ( Bibliographia Nudibranchia ( Encyclopedia of Life – online ( Nudibranchs of Florida ( Dive-OZ ( A Snail’s Odyssey – a journey through the research done on west-coast marine invertebrates ( Facts and Details: Nudibranchs (

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