Glaucus atlanticus Forster, 1777
|Maximum size: 35 mm.
flattened aeolid is midnight blue on the ventral surface
(facing upward in the photo) and silvery blue on the dorsal surface.
Its cerata extend laterally from three distinct pairs of lobes. In contrast to Glaucus marginatus, the cerata are arranged in a single, flat row along the edge of each lobe.
is rarely seen except during periods of on-shore winds which bring
them (and their prey) into coastal
waters. Then, they can be found in numbers floating on the surface and,
sometimes, even washed up on beaches. They are holoplanktonic, spending
their entire lives drifting with the foot oriented toward the surface.
partially by means of an air bubble that they have swallowed and stored
in their gastric cavity and are able to move toward prey or mates by
using their cerata to make slow swimming movements. They eat a variety
prey including the siphonophore Physalia
utriculus (Portuguese man-o-war) as well as the chondrophores Velella velella and Porpita pacifica (see photo). Occasionally, they
eat each other. Like many other aeolids, they store the nematocysts
prey in the tips of their cerata for protection against predators.
Unlike in most aeolids, the sting can
be felt by humans. The dark ventral coloration (which faces the sky)
may help in concealing them from birds while the light dorsal
coloration (facing down) may help in concealing them from fish.
However, some pelagic fish do feed on them. (Note 1) Their
egg mass is a straight thread of white eggs up to 17.5 mm long that
floats freely in the water (Ross and Quetin, 1990). These authors also
reported that freshly collected individuals produced 4-6 egg strings
per hour with 36-96 eggs per string and a total of 3300-8900 eggs
Big Island, Maui, Oahu, Kauai and Midway: cosmopolitan.
name means "bluish gray" and the species name refers to the
ocean from which it was first named. It is referred to as the
"man-of-war nudibranch" in Hoover, 1998 & 2006. It was first
reported from Hawaii in Bergh, 1860 (as Glaucus longicirrus) and was listed under that name in Edmondson, 1946.
washed up on Keawakapu Beach, Maui; Nov. 25, 2010.
Observations and comments:
1: We observed a pelagic
triggerfish (Canthidermis maculatus)