Author: Korshunova et al, 2017

Order: Nudibranchia  Family: Unidentiidae

Maximum Size: 8 mm

Sightings: Sunshine Coast

______________________________________________________________

Unidentia nihonrossija Korshunova et al, 2017

The genus Unidentia was raised by Millen & Hermosillo in 2012 to hold a single species – Unidentia angelvaldesi. Since then three other described species have been added, part of the reason for the slow sorting being the similarity of external appearance, hiding cryptic but not unexpected species.

Unidentia nihonrossija exhibits, in common with its fellow genus members, the following external morphology: a narrow body lacking a distinct notal edge, cerata on distinct elevations, well-developed anterior foot corners and smooth rhinophores. Unidentia nihonrossija possesses from five to seven bilateral clusters of cerata. The cerata are fusiform in appearance with long tapered apices and are substantially filled with the digestive diverticula. The rhinophores are shorter than the oral tentacles.

Much of the differentiation between Unidentia species, using photographs, relies almost solely upon the colours and their distribution upon the various visible anatomical features. Unidentia nihonrossija has a translucent white body and tail with some light opaque white regions upon the notum. Running down the midline of the dorsum there is a diffuse light purple line extending from anterior to the rhinophores to the tip of the tail. Both rhinophores and oral tentacles are translucent light purple with varying amounts of diffuse white pigment to their distal third. The cerata are translucent, each revealing an orange digestive diverticulum within. The long tapered tips of the cerata are translucent with a large band of white pigment subapically. At times, a narrow region of faint purple colouration can be observed just below and adjacent to the white band on some cerata.

Feeds on hydroid colonies.

The designation of the specific epithet is explained by the authors thus: “After nihon ( …. meaning “Japan” in Japanese) and rossija ( …. meaning “Russia” in Russian) in reference to the international group of Russian and Japanese scientists who organised the  field work in Japan, during which this unique representative of the family Unidentiidae was collected.”

Distribution: The Type Locality is Osezaki, Japan. There seem to be no other sightings recorded as yet outside of Japan, apart from our recording of it from the Mooloolah River, Sunshine Coast, Queensland, Australia.

David A. Mullins – February 2022

References:
– Millen, S.V. & Hermosillo, A. (2012). Three new species of aeolid nudibranchs (Opisthobranchia) from the Pacific coast of Mexico, Panama and the Indopacific, with a redescription and redesignation of a fourth species. The Veliger, 51, 145–164.

– Korshunova, T.A., Martynov, A.V., Bakken, T., Evertsen, J., Fletcher, K., Mudianta, W.I., Lundin K., Schrödl, M. & Picton, B. (2017). Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda). ZooKeys, 717, 1–139.

– Korshunova, T., Mehrotra, R., Arnold, S., Lundin, K., Picton, B. & Martynov, A. (2019). The formerly enigmatic Unidentiidae in the limelight again: a new species of the genus Unidentia from Thailand (Gastropoda: Nudibranchia). Zootaxa. 4551(5): 556-570.