Author: Korshunova et al, 2019

Order: Nudibranchia  Family: Unidentiidae

Maximum Size: 8 mm

Sightings: Sunshine Coast

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Unidentia aliciae Korshunova et al, 2019

This is the fourth species to be added to the Unidentia genus since it was raised in 2012 by Millen & Hermosillo. It had been expected that there would be a number of cryptic species in this group. It would appear that many can only be differentiated externally by the distribution and patterning of the predominant colours of purple and white on the dorsum, cerata, rhinophores and oral tentacles. Orange and red are mainly associated with the digestive diverticula within the cerata.

We have extracted this species from a collection on our website/database originally under the name of Unidentia sp. 01. They have been extracted on the basis of strict adherence to the external features listed in the species description. We have left in Unidentia sp. 01 those specimens that do not exhibit a distinctive wide tapering (tear drop) shape on the head anterior to the rhinophores and lack a gap to the purple midline between the rhinophores. It may be that those remaining in Unidentia sp. 01 are just specimens at one end of a spectrum of variation, but to avoid confusion are segregated on this site.

Unidentia aliciae is an aeolid nudibranch with a long narrow body and lacking a distinct notal edge. The foot too is narrow and the  tail not especially long such that the long trailing cerata normally obscure it from view. The long fusiform cerata arise in groups from distinct elevations on the lateral dorsum and terminate distally in long tapered apices. The rhinophores are smooth and tapered bearing eyespots at their bases. The oral tentacles too are smooth and of a similar length as the rhinophores but much more finely tapered distally.

The notum is translucent appearing creamy-white due to the viscera and acini showing through. A distinctive feature is the possession of a purple mark anteriorly on the head described as a “tear drop shape” by the authors that is wide anteriorly between the oral tentacles and tapers posteriorly to stop just anterior to the rhinophores. Following a gap between the rhinophores, just posterior to the rhinophores a narrow purple line recommences and continues, often interrupted, posteriorly to the tail. There is an additional thin purple line each side laterally on the notum commencing just posterior to the oral tentacle bases and continuing, interrupted, laterally to (beneath and obscured by) the ceratal bases, terminating just prior to the tail. The oral tentacles are heavily pigmented in purple on the basal half to two-thirds (sometimes for the complete length), often just upon the dorsal surface with the distal third to half pigmented in opaque white. The rhinophores are coloured similarly to the dorsum (lacking any purple pigment whatsoever) but carry opaque white pigment to the distal third or less. The dorsal surface of the propodial tentacles bear a purple stripe. The cerata are translucent with the orange digestive diverticulum showing through (this colour dependent upon recent predation and the strength of colour in that prey). The very tips of the cerata are translucent and below this is a wide band of opaque white pigment followed by a wide band of purple.

Feeds upon hydroid colonies, reported by the authors to be Corydendrium sp.

Spawn: The authors state that it is laid as a pale orange spiral upon its hydroid prey.

Distribution: The Type Locality is listed as Koh Tao, Thailand. There do not appear to be any other sightings recorded thus far apart from the Mooloolah River, Sunshine Coast, Queensland, a source, of what appear to be, many variants/undescribed cryptic species of Unidentia nudibranchs.

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.