Author: Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl, and Picton, 2017

Order: Nudibranchia  Family: Flabellinidae

Maximum Size: 25 mm

Sightings: Sunshine Coast

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Coryphellina lotos Korshunova, Martynov, Bakken, Evertsen, Fletcher, Mudianta, Saito, Lundin, Schrödl, and Picton, 2017.

Coryphellina O’Donoghue, 1929, was re-erected (from synonymy, first with Coryphella and latterly Flabellina) by Korshunova et al, 2017 and this species described and added to it. At the time its discontinuous dorsal and lateral lines made for easy identification although interestingly, no mention of the dorsal and lateral lines is mentioned, let alone the fact they are discontinuous, in the description by Korshunova et al, 2017 (p. 49) of Coryphellina lotos but this feature is evident in the accompanying images (Fig 38.). A sister species, Coryphellina pseudolotos, was described by Ekimova et al, 2022 (also redescribing Coryphellina lotos) that has an identical external morphology and difficult to delineate colouration. These two are the only described species of the Coryphellina genus where the dorsal and lateral lines are discontinuous (see below). The re-erection made Coryphellina rubrolineata O’Donoghue, 1929 the type species. Phylogenetic and morphological investigations of a number of specimens collected in Vietnam waters (Ekimoiva et al, 2022) found several cryptic species previously all lumped into Coryphellina rubrolineata. Additionally the findings have confirmed that Coryphellina rubrolineata rather than being a widespread tropical species is actually confined to its type locality and adjacent waters – Red Sea and Arabian Sea but also introduced into the Mediterranean Sea.

Form:
Typical aeolid form with slender body and foot. Anterior foot corners well-developed – tentacular. Oral tentacles 1.5 to 2 times rhinophore length and with tapered tips. Rhinophores are highly papillate on the posterior face and bear pointed tips. There are up to 6 ceratal groups on each side – first group largest, second and subsequent located posterior to the inter-hepatic space. Cerata on low elevations (slight pedunculate), cylindrical, elongated and pointed. Tail short, quickly tapering following posterior-most ceratal group.

Colouration:
– Background (body and notum): Translucent white to translucent purple.
– Oral tentacles: Same as body colour but with magenta or dark-pink wide band subapically, translucent tip.
– Rhinophores: Same as body colour or light-orange with magenta sub-apical band and translucent tips.
– Cerata: Translucent, same as body colour or very light-pastel-orange, magenta subapical band with white or pastel orange tip. Digestive diverticulum visible, light-orange.
– Mid-dorsal line: Discontinuous, thick on head, faint on body – pink to magenta in colour. (Many Sunshine Coast species we have recorded present with their interrupted mid-dorsal line as quite distinct.)
– Lateral lines: Discontinuous. Located just below notal edge and in regions between ceratal clusters – pink to magenta in colour.

It can be seen that there is variability in colour and also in the intensity of colours. This species is most difficult to delineate from the more recently described Coryphellina pseudolotos using external characteristics and colouration. Both are the only described species of Coryphellina exhibiting discontinuous lines. Large specimens (~20 mm), that are also translucent, are more likely Coryphellina pseudolotos. In reading the descriptions and reviewing the images supplied therein it may be deduced that Coryphellina pseudolotos has a translucent body without white or purple tint at any size. However, there is some conflict in the descriptions by Ekimova et al, 2022 concerning the comparison of these two species. On the one hand C. pseuodolotos is described as having a maximum length of 15 mm but in the Remarks paragraph there is a reference to specimens ~20 mm retaining their translucent appearance.

Note on Coryphellina:
As mentioned above, Coryphellina O’Donoghue, 1929, was re-erected by Korshunova et al, 2017. Since then its use has become frequent despite reservations from some taxonomists who cite that: some taxa were omitted, paraphyly was simply transferred and sampling was insufficient. Ekimova et al, 2022 conducted further molecular testing and subsequently identified and described four new closely related cryptic species and two putative species of Coryphellina. In order to stay in step with most common usage we are now using Coryphellina. There is no doubt that there is a clade involved. There is also no doubt there were issues of paraphyly in Flabellina previously and the splitting into additional genera such as Samla and Coryphellina may not entirely solve that issue, however, given the current usage (>4 years), it may be more confusing not to make the change at this point. Once larger sampling across more geolocations is undertaken a clearer picture may be resolved.

David A. Mullins – May 2022

References:
– Gosliner, T. M. & Willan, R. C. (1991). Review of the Flabellinidae (Nudibranchia: Aeolidacea) from the tropical Indo–Pacific, with descriptions of five new species. Veliger, 34, 97–133.

– Schulze, A. & Wägele, H. (1998). Morphology, anatomy and histology of Flabellina affinis (Gmelin, 1791) (Nudibranchia, Aeolidoidea, Flabellinidae) and its relation to other Mediterranean Flabellina species. Journal of Molluscan Studies 64: 195–214.

– Yonow, N. (2008). Sea Slugs of the Red Sea. Pensoft Publishers.

– Furfaro, G., Salvi, D., Mancini, E. & Mariottini, P. (2017 Online). A multilocus view on Mediterranean aeolid nudibranchs (Mollusca): Systematics and cryptic diversity of Flabellinidae and Piseinotecidae. Molecular Phylogenetics & Evolution, 118, 13–22.

– Korshunova, T., Martynov, A., Bakken, T., Evertsen, J., Fletcher, K., Mudianta, I. W., Saito, H., Lundin, K., Schroedl, 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 2017, 717, 1.

– Gosliner, T. M., Valde ́s, A ́. & Behrens, D. W. (2018). Nudibranch & Sea Slug Identification – Indo-Pacific, 2nd Edition. New World Publications, Jacksonville, Florida, USA.

– Ekimova, I., Deart, Y.,  Antokhina, T., Mikhlina, A. & Schepetov, D. (2022). Stripes Matter: Integrative Systematics of Coryphellina rubrolineata Species Complex (Gastropoda: Nudibranchia) from Vietnam. Diversity,14,294.