Hallaxa hileenae Gosliner & S. Johnson, 1994

Description

Body length 5-12 mm, elongate and ovoid. Background colour wine red. Opaque white pigment is present around the margins of the notum and gill, and on the elevated ridges of the notum. White pigment is also scattered around the rhinophores, becoming densest at the apex.
A thick longitudinal ridge runs mid-dorsally from between the rhinophores to anterior to the gills, where it divides into a pair of diagonal ridges that encircle the gills, forming a y-shaped elevated portion of the otherwise smooth notum. This is the most distinctive feature of the species. Submarginal areas of the notum bear irregular charcoal gray to black markings and a few scattered opaque white spots.
The gill consists of 6-8 unipinnate leaflets, and the bulbous rhinophores have 5-6 lamellae.

Distribution

Papua New Guinea, the Philippine Islands, and Guam.

Etymology

The specific epithet hileenae honours Eileen Sobeck, who assisted in fieldwork in Papua New Guinea and collected the first specimen of the closely related Hallaxa iju. "Hileen" is the Papua New Guinea pidgin form of the name "Eileen".

Remarks

Most closely related to Hallaxa indecora in sharing a purplish body colour, but distinguished externally by the characteristic y-shaped dorsal ridge and the black notal maculations. Reproductive characters place it within the derived clade also containing Hallaxa cryptica and Hallaxa michaeli.

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References

• Hallaxa hileenae sp. nov., Gosliner T.M. & Johnson S. (1994). Review of the genus Hallaxa (Nudibranchia: Actinocyclidae) with descriptions of nine new species. The Veliger. 37(2): 155-191.
• アメシストウミウシ（新称）, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.