Melibe leonina (Gould, 1853) Common name(s): Lion nudibranch
Synonyms:  Chioraera leonina, Chioraera dalli
Phylum Mollusca  Class Gastropoda   Subclass Opisthobranchia    Order Nudibranchia     Suborder Dendronotacea      Family Tethyidae
	Melibe leonina about 10 cm long.  Collected from eelgrass at Padilla Bay.  The head and oral hood is to the right.  Some of the tentacles from the opening in the oral hood can be seen.
	(Photo by: Dave Cowles July 2006)

How to Distinguish from Similar Species:  This is the only local Dendronotacean with a huge oral hood

Geographical Range:  Kodiak Island, Alaska to Gulf of California, Mexico.  Mostly offshore in kelp beds south of Puget Sound

Depth Range:  Low intertidal to 37 m

Habitat:  Eelgrass beds, kelp (especially Macrocystis) beds, harbors

Biology/Natural History:  This nudibranch is unusual in several ways.  It lacks a radula, but its oral veil is expanded hugely into a hood which it extends ahead of itself and uses to trap small crustaceans and other prey.  Its diet includes copepods, amphipods, and ostracods, as well as small post-larval mollusks.  The animal stands attached to the substrate (often a blade of eelgrass) and expands the oral hood.  It then sweeps the hood left and right or downward (photo).  When the ventral surface of the hood contacts a small animal the hood rapidly closes and the fringing tentacles overlap, holding the prey in.  The whole animal is then forced into the nudibranch's mouth.  Predators include the kelp crab Pugettia producta.  Pycnopodia helianthoides is repelled from contact.  The polychaete scaleworm Halosydna brevisetosa is sometimes a symbiont, feeding on fecal pellets.  Some may have symbiotic algae.

Branches of the gut extend out into the cerata.  The name is due to the large hood which may look like a lion's mane.

This species hunts mainly attached, but is a good swimmer (movie).  When swimming it is usually upside-down, and thrashes or undulates back and forth.  It is often seen swimming near the water's surface in the summer (movie), or after fall and winter storms disturb the eelgrass.  Eggs are laid in long, wide yellow or cream-colored ribbons in the summer, which are attached to kelp and eelgrass. The ribbons form tight coils or wavy folds.  Eggs can be found in the Washington area at any season.  They appear to live about one year, reciprocally fertilize one another (as with most nudibranchs they are hermaphrodites), lay their eggs and die.  This species has been used for neurological research.

According to Baltzley et al., (2011), many gastropods, including this species, have a special network of pedal ganglia in their foot which assists in crawling.  The two main neurons involved produce pedal peptides which elicit an increase in the rate of beating of cilia on the foot, resulting in crawling.

References:

General References:
  Behrens, 1991
  Harbo, 1999
  Johnson and Snook, 1955
  Kozloff, 1993
  Morris et al., 1980
  Niesen, 1997
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Wrobel and Mills, 1998

Scientific Articles:
 Baltzley, Michael J., Allison Serman, Shaun D. Cain, and Kenneth J. Lohmann, 2011.  Conservation of a Tritonia pedal peptides network in gastropods.  Invertebrate Biology 130: 4 pp. 313-324

Web sites:
 

Click here for a short closeup video of this species swimming in a tank

 
Melibe leonina swimming near surface, about 3 m from the bottom, in a harbor.  Length about 8 cm  Click the photo for a short video of this individual swimming

Click here for a movie of another individual swimming in a planktonkreisel (Dave Cowles, 2018)

This is a top left view of a swimming individual, who has been swimming away but is making a strong turn to the left.  The head and oral hood are visible to the right.
The flaplike extensions of the oral hood are the rhinophores.
The large dorsal cerata with an internal network of vessels (hepatic diverticula?) are visible at the top and right.  The foot is facing down and away from view.
The oral hood is closed in this view.

In this nearly head-on view the open oral hood with its filiform tentacles can be seen.

This cluster of eggs, about 2.5 cm across, was laid attached to a wall of a planktonkreisel by Melibe leonina. Photo by Dave Cowles, July 2018