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young, 8 mm

with egg mass

Gymnodoris bicolor
(Alder and Hancock, 1866)
Gymnodoris bicolor
Maximum size:  22 mm (Kay, 1979).

Identification:  The background color of this species varies from cream through orange to pale pink. It's decorated with small orange spots. The branchia form a horseshoe-shaped circle around the anus and the oral tentacles are broad. It can be distinguished from the similar-appearing Gymnodoris sp. #2 by its lack of nipple-like tips on its rhinophores and its broad oral tentacles. It can be distinguished from the nearly identical Gymnodoris citrina be the location of its genital opening  (immediately behind the branchia in G. bicolor and well forward of the branchia in G. citrina) and by its more rounded oral tentacles.

Natural history:  Gymnodoris bicolor is a moderately common species found in protected to moderately exposed rocky habitats at depths of < 1 to 10 m (< 3 to 33 ft). Like G. citrina, it feeds on other species of Gymnodoris. (Kay, 1979) (Note 1) It lays an orange to cream, spiral egg mass that hatches in about eight days in the laboratory.

Distribution:  Big Island, Maui, Oahu, Kauai and French Frigate Shoals: widely distributed in the Indo-Pacific.

Taxonomic notes:  It was first reported from Hawaii in Kay & Young, 1969.

Photo:  CP: orange: Hekili Point, Maui; Oct. 19, 2001.

Observations and comments:

Note 1:  On July 4, 2012 an 8-10 mm Gymnodoris bicolor was offered a Noumeaella rehderi, an Elysia sp. #6 and a Gymnodoris alba (or G. sp. #7?), all around 3-4 mm in length. It ignored the first two (even with repeated contact) but immediately ate the G. alba.
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