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Additional Photos

side

underside

tan

white

yellow

young, 4 mm

feeding

egg mass
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GALLERY

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Favorinus japonicus Baba, 1949

Maximum size: 17 mm (Kay,
1979).
Identification:
This aeolid has a translucent white body with opaque white patches on
the head and along the length of the notum. The color of its cerata
varies depending on what type of eggs it has been eating--generally in
Hawaii they range from white to pink. The rhinophores are translucent
at the base, white at the tips and have two characteristic swellings on
the distal half. It may be distinguished from the similar appearing Favorinus
sp. #1 by the lack of violet spots in the tips of the cerata.
Natural history:
Favorinus japonicus
is a common species that can be more easily found than many
other aeolids due to its habit of eating (and laying eggs on) the egg
masses of other opisthobranchs, particularly those of Hexabranchus spp. However, it's
primarily nocturnal and may also be found crawling in the
open at night, presumably seeking mates or new egg masses to feed on.
It
inhabits moderately protected to highly exposed rocky environments as
well as Halimeda kanaloana
beds from <
1 to 27 m
(< 3 to 90
ft). It eats a
wider variety of opisthobranch egg masses than other Favorinus spp. We've seen them on Dolabrifera dolabrifera, Hexabranchus and
pleurobranch egg masses while Kay, (1979) also reports them eating Aplysia and Melibe eggs. Retention of pigments
from its food produces its highly variable coloration. It lays a white
egg mass of many low
whorls, often on the egg mass it's feeding on. In the latter case, in
order to survive, its
eggs must hatch before or just after the food egg mass, probably in
less than a
week.
Distribution:
Big Island, Maui, Lanai, Oahu, Kauai and Midway: widely distributed in the
Indo-Pacific.
Taxonomic notes:
It's referred to as the "egg-eating nudibranch" in Hoover, 1998
& 2006 and was first reported from Hawaii in Gosliner, 1980.
Photo: PF: 11
mm: off Lualailua, Maui; March, 1990.
Observations and comments:
Note
1: ( )
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