Giant Nudibranch, Dendronotus iris
Giant Nudibranch, Dendronotus iris. Underwater photographs taken in the coastal waters off Monterey, California, February 2022. Photographs and identification courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The Giant Nudibranch, Dendronotus iris (J. G. Cooper, 1863), is a member of the Dendronotidae Family of Nudibranchs. The genus Dendronotus is one of three genera in the Dendronotidae Family, and there are thirty-seven species in the Dendronotus genus. They are also known as the Barber Nudibranch, the Giant Dendronotus, the Giant-frond Aaeolis, and the Rainbow Nudibranch. In Mexico they are called Dedronotus de Arco Iris. The specific name iris comes from the mythological Greek goddess of the rainbow.
Morphology: Giant Nudibranchs appear to be shaggy nudibranchs because of their branched gills and cerata. The bushy cerata are arranged into two longitudinal dorsal rows. The oral veil has four pairs of papillae. The rear edge of the rhinophores have 3 to 6 branched processes. They vary in color from translucent white or gray, to orange or red. They generally have a white edge around the foot, though this may be absent. The branched gills may be tipped with orange, yellow, white, or purple. These are large nudibranchs, reaching 20 cm (7.9 inches) in length, but most specimens are about half that size.
Habitat and Distribution: Giant Nudibranchs are found on mud or sand bottoms from the lower intertidal zone to depths of 200 m (660 feet). They are a temperate to subtropical Eastern Pacific species. In Mexican waters the Giant Nudibranch has a limited distribution. It is found only along the west coast of the entire Baja Peninsula.
Diet: Giant Nudibranchs are predators, feeding on the Tube-dwelling Anemone Pachycerianthus fimbriatus. They graze over the tentacles of the anemone, leaving the anemone alive. This “tentacle haircut” is what gives them the common name Barber Nudibranch. On occasion, they are so committed to feeding on the tentacles that they are pulled down into the anemone’s tube, as the anemone retracts. The nudibranchs retain the toxin of the anemones, incorporating it for their own defense. Giant Nudibranchs are also known to eat hydroids, nemateran worms, and scyphistomae jellyfish.
Predators: The Giant Nudibranchs possess toxic tipped cerata and they can rapidly swim through the water by quickly bending and straightening their body to avoid predation. They are preyed upon by crabs, polychaetes, sea spiders and sea stars including the Sunflower Star, Pycnopodia helianthoides.
Reproduction: Giant Nudibranchs are simultaneous hermaphrodites (having both male and female reproductive organs). They reproduce sexually. Copulation requires two individuals to face opposite directions, with their right sides touching. They pass sperm packets through a tube called the copulatory apparatus. After being fertilized internally, the eggs are laid in white, gelatinous, strings, often on the tubes of their prey. These egg masses can contain millions of eggs. After four to seven weeks, the eggs hatch into planktonic larva.
Ecosystem Interactions: The commensal and parasitic relationships of the Giant Nudibranch has not been documented.
Human Interactions: Giant Nudibranchs 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: None