young, 1 mm
with egg mass
Plakobranchus ocellatus van Hasselt, 1824
|Maximum size: about 64 mm
in being dorso-ventrally flattened with
broad parapodia that meet in the center of the notum and rhinophores
that extend laterally. Its translucent, gray-cream body is decorated
with yellow-centered and
blue-centered ocelli and there are purple highlights on the rhinophore
posterior margin. Beneath the parapodia are longitudinal green ridges.
is the most commonly seen plakobranchid in sandy and mixed habitats
from < 1 to 18 m (3-60 ft). It occurs in highly protected to
protected back reef areas and in Halimeda
kanaloana beds at
Active crawling and mating are often crepuscular with the animals
spending much of the time both by day and night resting passively on
the bottom with a fine layer of sand covering their bodies (sometimes, in groups).
derived from their food are retained in the ridges beneath their
parapodia and may be providing much of their nutrition. (Note 1) The egg mass is
a cream, irregular spiral with a ribbon diameter of about 1 mm. It is
typically laid on algae such as Halimeda and Acanthophora. (Kay, 1979) (Note 2)
Big Island, Maui, Oahu, Kauai, French Frigate Shoals, Midway and Kure:
distributed in the
for the blue and yellow centered ocelli that
cover the body and it's
referred to as the "ringed sap-sucking slug" in Hoover, 1998 &
2006. It was first reported from Hawaii in Gould, 1852 (as Placobranchus ianthobapsus) and is listed under that name in Ostergaard, 1955. Elysia ocellata Pease, 1860 and Placobranchus argus Bergh, 1872
are also synonyms. It's listed as Placobranchus sp. in Edmondson,
1946 and Ostergaard, 1950. The species will probably be split, at some
point, per Krug, et. al., 2013 (though it's likely that there will only
be one species in Hawaii). When that happens, the Hawaiian population will probably be named Placobranchus ianthobapsus Gould, 1852.
Airport Beach, Maui; June 21, 2005.
Observations and comments:
1: Conceivably, the translucent
tissue of the parapodia may be filtering or focusing sunlight in such a
way as to optimize its spectrum or intensity for the retained
chloroplasts (perhaps, in conjunction with the sand layer retained on
the body surface?).
Note 2: Many times we've
seen this species resting on top of the sea cucumber, Holothuria whitmaei, at night. (see
photos) However, the association may be coincidental since the cucumber covers itself with a thin layer of sand.