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This species was described by Bergh (1905) as Halla indecora, but the genus Halla was preoccupied by Halla Costa, 1844, Hallaxa is a replacement name.
Bergh (1905) described it from 9 specimens collected at the East coast of the Aru Islands, Indonesia. This decription was on preserved specimens, in German and pretty poor - translated by me: colour solid white including gills and rhinophores.
Identifyable only by the drawings of the radula, plate XV, fig. 3 - 6.
Gosliner & Johnson (1994) redescribed this species. Let me quote page 174:"External morholopy: The living animal is light plum in appearance. Upon closer examination, the notum is translucent white with minute, scattered maroon spots. The body is elongate and ovoid with a smooth notum. The rhinophores and gills are uniformly purplish-brown. The rhinophores are bulbous with seven lamellae. The branchial plume consists of seven unipinnate gills. The foot (Figure 22A) is curved anteriorly, and the anterior foot corners are thin and anteriorly directed. A pit is present on either side of the mouth."
They extended the distribution from the Gulf of Suez to Okkinawa, Japan.
Scott Johnson writes at his website:"Most specimens have a hump on their backs just in front of the gills." Which was not mentioned by Bergh (1905) nor by Gosliner & Johnson (1994).
Bergh, L.S.R. (1905). Die Opisthobranchiata der Siboga-Expedition. Monographie 50: 1 - 248, pls. 1 - 20
Gosliner T.M.; Johnson S. Review of the genus Hallaxa (Nudibranchia: Actinocyclidae) with descriptions of nine new species.
The Veliger. 37(2): 155 - 191. available online at http://biodiversitylibrary.org/page/42464857
Gosliner, T.M, D.W. Behrens & Á.Valdés. 2015. Nudibranch & Sea Slug Identification Indo-Pacific.
New World Publications Inc. Jacksonville, FL. 408 pp.
More information on Hallaxa indecora are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2020), published 31 May 2020, Hallaxa indecora (Bergh, 1905)
available from http://www.Philippine-Sea-Slugs.com/Nudibranchia/Doridina/Hallaxa_indecora.htm