“Resurrecting” species: the case of the sea slug Dendrodoris temarana

by Manuel Ballesteros
Facultat de Biologia, Universitat de Barcelona, Spain, mballesteros@ub.edu

A scientific article (Galià-Camps et al., 2022) has been recently published in which the validity of a “forgotten” sea slug species (Mollusca, Gastropoda, Nudibranchia) was reinstated, as it had been considered a synonymous of other Mediterranean species. Here I tell the story of Dendrodoris temarana Pruvot-Fol, 1953 in the scientific literature and also “my story” with it, with numerous personal experiences related to it, some data of scientific interest and comments about the species.

Dendrodoris temarana Pruvot-Fol, 1953 by Manuel Ballesteros

Alice Pruvot-Fol
First of all, I would like to briefly introduce the author who described the species: Alice Pruvot-Fol. This remarkable French researcher (1873-1972), little known to non-specialists in molluscs, was the wife of another renowned professor and zoologist at the Faculty of Sciences in Paris, Georges Pruvot, a specialist in polychaete annelids. Although she started late in her life, Alice had a long and productive scientific career, publishing numerous papers on “opisthobranch” mollusks and also on the anatomy of mollusks such as the buccal bulb and radula. Her first publication dates from 1922 and the last from 1963, at the age of 89 (Pruvot-Fol, 1963), where she describes the species of nudibranch Phyllidia pulitzeri, currently synonymized with Phyllidia flava. Throughout her scientific life, she described more than 80 new valid species of “opisthobranchs”, in addition to creating new genera and families. Perhaps the culmination of all her scientific work is the book Faune de France. Mollusques Opisthobranches (Pruvot-Fol, 1954), a mandatory reference when studying European “opisthobranchs”.

Dendrodoris temarana
Pruvot-Fol described Dendrodoris temarana thanks to specimens collected in the town of Temara, on the Atlantic coast of Morocco. The author made the description of the species based on preserved specimens and she never saw the animals alive (Pruvot-Fol. 1953). The only data on the coloration of living animals come from a watercolor drawing made by the naturalist artist Hélène Gantés (Figure 1). In the original description, Pruvot-Fol also indicates that the animals have a certain chromatic variability, with specimens having a yellow or brown tone and other dark ones, almost black. In the color illustration it can be seen that the specimen has irregular spots on the back and that the edge of the mantle is wide. The author adds at the end of her description that the species that most closely resembles temarana is Dendrodoris longula, also described by her and which is currently considered a synonymous species with D. grandiflora. After the description of Dendrodoris temarana and in the absence of new specimen collections, the species fell into oblivion. In addition, different authors (Ballesteros, 1978; Valdés et al., 1996) consider D. temarana as synonymous with other Dendrodoris species such as D. limbata and D. grandiflora. It should be mentioned that the species of the Dendrodorididae family, to which the Dendrodoris genus belongs, lack a radula in their buccal bulb, so for their identification reference must be made to their external morphology, coloration and in certain cases also their internal anatomy. The intraspecific chromatic variability of some species makes their correct identification sometimes extremely difficult, which is further complicated if the coloration of the specimens varies as they grow larger, as is the case of D. temarana.

“My personal story” with Dendrodoris temarana
It all started in Cubelles, a coastal town located about 50 km south of Barcelona (NE Spain). For years Cubelles was the preferred place for the Zoology teachers of the Faculty of Biology of the University of Barcelona to carry out field trips with the students to observe marine fauna. In the mid-70s of the 20th century I was one of those biology students and the field trip to Cubelles pleasantly surprised me because at a depth of less than a meter you could see numerous species of benthic invertebrate fauna that lived above or below of the numerous stones (pebbles) that covered the sandy bottom and that had been contributed to the sea by the floods of the Foix river, which flows into the same beach (Figure 2).

At that time I met Dendrodoris temarana, a common species in the area. It was also the time when I got excited about nudibranchs; some plates of color photographs of nudibranchs made by J.D. Ros and those who illustrated the great work Ecología (1974) by Ramón Margalef were mainly to blame. Already graduated, I carried out a study on the benthic fauna of Cubelles for the doctoral subject “Marine benthic communities” and which was later published (Ballesteros, 1978). In this study I counted numerous specimens of Dendrodoris temarana, which at that time I identified as Dendrodoris limbata, I was able to verify the great chromatic variability of the species, with even melanic specimens, its large size of up to 70-80 mm and that the town of Cubelles represented for this species a very suitable environment to live, feed and reproduce. I myself contributed to the identification error of D. temarana, an error that was also reflected in my doctoral thesis report (Ballesteros, 1980), illustrated by the drawings of Figure 3. Figure 4 shows the chromatics traits of two of the largest specimens collected in Cubelles (approximately 70 mm in length).

Years later Valdés et al. (1996) carried out an analysis of the North Atlantic Dendrodoris species where they describe several new species such as Dendrodoris herytra and redescribe the already known ones; among these is Dendrodoris grandiflora in which these authors frame the Cubelles specimens. This new identification error of Dendrodoris temarana has been maintained, including records at the World Register of Marine Species (WoRMS) website, until the publication of Galià-Camps et al. (2022).

However, I had always doubted that identification because the Cubelles specimens did not appear in other towns on the Catalan coast, and whether they really belonged to Dendrodoris grandiflora, since this species, relatively common on the Catalan Costa Brava, had a very different chromatic pattern, quite homogeneous, with a greyish mantle with greenish irregular spots. Also, the new species Dendrodoris herytra was a candidate for the Cubelles specimens, since some specimens had an homogeneous reddish colored notum, typical of D. herytra; or even the Cubelles specimens could be a species new to science…

More years go by, and the time has come to finally “unmask” the Dendrodoris de Cubelles. It is 2015 and Carles Galià-Camps is working on his final degree project (TFG), under my supervision, on the population of Dendrodoris from Cubelles. The aim was to learn about the annual cycle of the species in that locality, discover its food preferences and genetically characterize the species through molecular analysis to clarify its identification. Some of the results of the TFG by Carles Galià-Camps (2016) have yet to be published, but it became clear that, molecularly speaking, the specimens of Cubelles were neither D. limbata nor D. grandiflora. So, were the Cubelles animals a new species? or a known species not studied in the TFG?

We began to consider the idea that the Cubelles specimens were a species new to science, so we even gave it a name before birth: Dendrodoris inchi. We obtained specimens of Dendrodoris herytra from Galicia, Dendrodoris krebsii from Cuba, Dendrodoris senegalensis from Cape Verde and specimens with a morphology very similar to those of Cubelles from the Portuguese coast, Cádiz, the Canary Islands and Cape Verde. The work was growing and Dr. Ángel Valdés from California State Polytechnic University Pomona and Dr. Juan Lucas Cervera from the University of Cádiz joined the Dendrodoris study team, their knowledge and suggestions very valuable for improving the quality of the work.

The molecular analysis carried out on all these specimens indicate that the specimens from Cubelles, together with those from Cádiz, the Canary Islands, Portugal and some from Cape Verde, differed significantly from D. herytra, D. limbata, D. krebsii, D. senegalensis and D. grandiflora, so they would belong to a different species. D. grandiflora was the closest species, as it is separated by a genetic distance of 8-10%, while the genetic differences between the unknown species specimens from different areas vary between 0 and 3%, falling within the accepted genetic variations for a single species. This confirms that the specimens of Dendrodoris from Cubelles were not the only ones of its species; they were the same species than those from Cape Verde to the western Mediterranean, the Canary Islands, the Portuguese coast and the coast of Cádiz (Spain).

When we were beginning to describe the presumed new species, Dendrodoris inchi when, almost by chance, we came across the plate by Pruvot-Fol (1953) and the color drawing of Dendrodoris temarana. We suddenly realized that our D. inchi could actually be D. temarana. Type specimens of temarana are lost, so thanks to some contacts of Juan Lucas Cervera we were able to obtain some new specimens of Dendrodoris temarana collected from the type locality, Temara, in Morocco. The molecular results of these new temarana specimens indicate that our unknown specimens, those from Cubelles and those from other geographical areas, were the same species. So Dendrodoris inchi died before birth and we “resurrected” a forgotten species, Dendrodoris temarana, that was considered synonymous with other species. After almost 70 years of being described to science, we proved that Pruvot-Fol was right about the validity of this species. My story with the Dendrodoris of Cubelles also ended happily…

The chromatic variability of D. temarana and its differences with other European Dendrodoris species

The variations in the coloration of some species of nudibranchs sometimes make their specific determination difficult and this can produce identification errors. Figure 5 shows the chromatic variations of the three species of Dendrodoris from the Mediterranean and the near Atlantic: Dendrodoris temarana (A), Dendrodoris limbata (B) and Dendrodoris grandiflora (C).

It can be seen that D. temarana and D. grandiflora have a very wide mantle margin, scalloped and with radial striations, while in D. limbata it is narrow and generally has a narrow yellowish stripe on the edge, hence the name of limbata of the species (among other meanings, limbo = end of a thing). Both D. temarana and D. limbata are highly variable chromatically, especially the former, and dark or melanic forms can frequently be seen in both species. On the other hand, D. grandiflora has a more homogeneous coloration, with the mantle almost always with a grayish or cream background color, with irregular greenish or brown spots. The underside of the mantle, the foot and the sides of the foot have spots in D. limbata, there are only spots on the sides of the foot in D. grandiflora while in D. temarana there are no spots on the underside of the mantle nor on the sides of the foot.

Another difference between these species is the eggs spawn: in temarana and grandiflora it is a coiled ribbon in several spiral turns with small white eggs while in limbata it is a ribbon with only one and a half turns and very large yellowish eggs since this species has direct development, without free-living larvae (Figure 6).

Finally, and as a general conclusion, molecular biology has proven to be a very useful and definitive tool to separate species and to know the true affinities between other taxa and large groups of living beings. Molecular techniques are elucidating the so-called species complexes, creating new species that, until now, were cryptic or, as is the case with D. temarana, confirming that some described species have different coloration morphotypes.

References

• Ballesteros, M. 1978. Contribución al conocimiento de la fauna bentónica de Cubellas. Publicaciones del Departamento de Zoología, III, 11–23.
• Ballesteros, M. 1980. Contribución al estudio de los Ascoglosos y Nudibranquios. Tesis Doctoral, Universidad de Barcelona.
• Galià-Camps, C. 2016. El gènere Dendrodoris Herenberg, 1831 (Mollusca, Heterobranchia, Nudibranchia) a Catalunya (Mediterrani occidental). Estudis poblacionals i ecològics i delimitació d´espècies mitjançant análisis mol·leculars. Treball Final de Grau en Biologia, Universitat de Barcelona.
• Galià-Camps, C., Cervera, J. L., Valdés, Á., Ballesteros, M. 2022. Attack on crypsis: Molecular and morphological study of Dendrodoris Ehrenberg, 1831 (Mollusca: Gastropoda: Nudibranchia) from the Mediterranean Sea and Northern Atlantic Ocean reinstates Dendrodoris temarana Pruvot-Fol, 1953. Zootaxa. 5133(3): 383-406
• Margalef, R. 1974. Ecología. Omega, Barcelona.
• Pruvot-Fol, A. 1953. Etude de quelques Opisthobranches de la côte Atlantique du Maroc et du Senegal. Travaux de l’Institut Scientifique Chérifien. 5:1-105.
• Pruvot-Fol, A., 1958. Mollusques opisthobranches. Faune de France. Paris, Lechevalier: 1-457
• Pruvot-Fol, A. 1963. Deux très rares nudibranches de la Méditerranée. Bulletin de la Société Zoologique de France. 87: 566-569
• Valdés, A., Ortea, J.A., Ávila, C. & Ballesteros, M. 1996. Review of the genus Dendrodoris Ehrenberg, 1831 (Gastropoda: Nudibranchia) in the Atlantic Ocean. Journal of Molluscan Studies, 62 (1), 1-31.
• WoRMS. 2022. https://www.marinespecies.org/

 

Note. In this article, the name of “opisthobranchs” is cited on several occasions; the name of this group of gastropod molluscs, which includes sea slugs in a broad sense such as sea hares, sacoglossans and nudibranchs, among others, currently has no taxonomic category, since modern molecular analysis techniques have confirmed that it is a polyphyletic group. But despite this, the name “opisthobranchs” is still used between quotation marks in popular science writings to refer to this traditional group of hermaphroditic marine mollusks and in which the shell is reduced, has become internal or simply does not exist in adult specimens.

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