Frontonia (Pe- Niculia, Oligohymenophora, Ciliophora) Species Descriptions and Redescriptions

Protistology 13 (1), 36–41 (2019) Protistology

On the importance of attentive reading of re- search articles: the case study of Frontonia (Pe- niculia, Oligohymenophora, Ciliophora) species descriptions and redescriptions

Sergei I. Fokin

Department of Biology, University of Pisa, 56126 Pisa, Italy; Department of Inverte- brate Zoology, St. Petersburg State University, and St. Petersburg Branch of the S.I. Vavilov Institute of History of Science and Technology, Russian Academy of Sciences, 199034 St. Petersburg, Russia

| Submitted December 20, 2018 | Accepted January 18, 2019 |

Summary

A commonly encountered problem of ignoring or inattentive reading of scientific articles by some protistologists of the past and present has been revealed using the case study of taxonomy of the ciliate genus Frontonia. The comparison between materials from literature and own investigations allowed the author to conclude that F. vernalis Ehrenberg, 1833 cannot to be a valid species and assume that it is rather a cluster of closely related freshwater ciliates with one contractile vacuole and a stable ability to accommodate green algae as the cytoplasmic symbionts. “F. vernalis”, as described by Bullington (1939), was shown to have little in common with the original description by Ehrenberg and most likely is a brackishwater ciliate similar to F. fusca. F. oculiaris described by the same author (Bullington, 1939) is obviously F. fusca, and the name “F. oculiaris” should be considered as a younger synonym of the latter. Thus, redescription of F. oculiaris (Pan et al., 2013b) should be treated just as a morphological study of the local Chinese population of F. fusca. The redescription of F. canadensis from brackish waters by the same authors can be considered as a description of a new species that has little in common with the original description of this freshwater ciliate (Roque and Puytorac, 1972). Recent phylogenetical reconstructions indicate the necessity to split Frontonia into several genera.

Key words: Frontonia, morphology, phylogeny, species redescription

Introduction tigations. At the same time, peniculines are important components of natural ciliate communities being Among Oligohymenophorea (Ciliophora, Pro- numerous in many different biotopes, mainly due to tista), the subclass Peniculia is one of the best know the representatives of two related genera – Frontonia and, in some aspects, intensively studied groups and Paramecium (Corlis, 1979; Puytorac et al., 1987; of ciliates. A few of these organisms became good Strüder-Kypke et al., 2000; Lynn, 2008; Foissner and promising model objects for laboratory inves- et al., 1994, 2002; Fokin and Trivashkevitch, 2004;

Fokin et al., 2004, 2006; Fokin, 2008; Gao et al., 1858), then one century later (Bullington, 1939) 2008; Long et al., 2008; Fokin, 2010/2011; Pan et and, finally, in the last decade numerous cases were al., 2013b; Cai et al., 2018). Frontonia is the largest revealed when researchers were demonstrating genus of the group, comprising more than 40 species ignorance or misinterpretation of the previously according to published data. However, only about published results. These phenomena sometimes 10 of them are the relatively common species (Kahl, caused significant taxonomic errors and instead of 1931, 1943; Dragesco, 1970; Roqui and Putorac, clarifying the situation were making it even more 1972; Dragesco and Dragesco-Kernéis, 1986; confusing. As an example, let’s take a closer look at Carey, 1992; Foissner et al., 1994, 2002; Fokin and the initial stages of description of the members of Trivashkevitch, 2004; Gao et al., 2008; Fokin et al., the genus Frontonia. 2017; Cai et al., 2018; Fokin et al., 2019). Frontonia representatives are widely spread in many types of THE HISTORY OF DESCRIPTION AND REDESCRIPTION OF water bodies (freshwater, brackishwater and marine) SOME FRONTONIIDS as well as in soil (Foissner et al., 2002). At the first glance, ciliates of the Frontonia group The first case is F. vernalis. Frontonia as a parti- look quite similar to each other from the morpho- cular ‘type’ of ciliate protists was first mentioned by logical point of view and the whole genus looks like Ch. G. Ehrenberg as early as in 1833 under the name a solid entity. These ciliates are characterized by of Bursaria vernalis (Ehrenberg, 1833, p. 235–236), the same type of stomatogenesis (bucco-kinetal) and then in 1838 under the same name, but with the with a distinctive set of oral membranelles (oligo- indication that this species belonged to subgenus hymenimum): 3 penniculi on the left side of the Frontonia (Ehrenberg, 1838, p. 329). According to buccal cavity and paroral membrane on the right the author’s “Polygastric theory” proposed in 1838 buccal margin. Topographically, somatic ciliature in his monograph entitled “Die Infusionthierchen is uniformly organized with some exceptions at als Vollkommene Organismen” (“The Infusion the oral region (vestibular and postoral kineties) Animals as Comprehensive Organisms”), all those and distinctive pre- and postoral sutures; typical “animalcula” – protozoa, bacteria, diatoms, des- trichocyst-like extrusomes are always present in mids and rotifers – were considered as tiny though the cortex. At the same time, some morphological perfect creatures organised in the same way as hig- features (e.g., number and structure of contractile her animals. In his monograph (Atlas, Table 34, vacuoles and micronuclei, as well as the cell size) Fig. VII), Ehrenberg simply reproduced the main are strongly variable within the group. It is quite drawing of F. vernalis made in 1833 (p. 383, Plate probable that F. leucas (Ehrenberg 1838), one of the III). Despite quite primitive description of Frontonia first described Frontonia species (type species of the made in both abovementioned publications, the genus has not yet been established), which manifests scientist indicated several important features of the huge size variation (from 100 to 500 µm), in fact new ciliate: size about 200–250 µm (1/10–1/12 is a group of sibling species (Foissner et al., 1999; of line=2,54 mm); body, which was uniformly Fokin et al., 2006). The first phylogenetic analysis elongated, ovoid, dorso-ventrally flattened with using 18S rRNA gene sequences of a number of the some reduction of size at the end of the cell, with genus’ representatives showed that Frontonia is a elongated oral aperture (around 1/5–1/6 of body – non-monophyletic group (Andreoli et al., 2007a, according to the drawings); 2 contractile vacuoles 2007b). This conclusion was confirmed using an (CV – he treated these structures as seminal vesicles) another set of different frontoniids (Gao et al., with particular location (anterior and posterior 2008), and later this fact was demonstrated several third of the cell, dorsally), and numerous green times again (e.g., Fan et al., 2013; Fokin et al., 2017, particles of 4–5 µm in diameter in the cytoplasm. 2019; Cai et al., 2018). Food vacuoles were mainly filled with Oscillatoria During the recent decade, a number of articles (cyanobacteria) and Navicula (diatoms). Ciliates dealing with Frontonia spp. were published, but in moved with rotation along the body axis, and some some of those articles several mistakes which pro- of them were recorded as dividing longitudinally. bably could be just due to the insufficient knowledge The latter observation apparently indicated that of old (and also not so old) literature were revealed Ehrenberg saw the conjugants that very often appear (Fokin et al., 2017). in the just collected samples. Importantly, the new In fact, starting from the middle of the XIX ciliate was collected by the scientist nearby Berlin century (Dujardin, 1841; Claparède and Lachmann, (at the zoo), in fresh water. It was not indicated by 38 · Sergei I. Fokin

Ehrenberg how many cells were investigated; thus, confusing that Pan with co-authors claimed that “in we can doubt that 2 CV is a stable feature. Later on, the original description of F. canadensis Roque and several times F. vernalis was synonymized with F. Puytorac gave neither a clearly outlined diagnosis nor leucas (Dujardin, 1841, Claparède and Lachmann, details of the living morphology” (Pan et al., 2013a, 1858; Kent, 1880-1882; Schewiakoff, 1889, 1896), p. 69), as if the assignment of the newly found ciliate and then again these frontoniids were accepted as to the name F. canadensis by Roque and Puytorac two different species (Kahl, 1931, 1943). (1972) was not justified at all. Meanwhile, comparison of the materials pre- Meantime, already in 1931 A. Kahl briefly sented as F. vernalis at the very beginning of its his- discussed taxonomical situation with F. vernalis tory (Ehrenberg, 1833, 1838) with the characteristics and logically compared it with F. leucas, as both of of a ciliate “redescribed” as F. vernalis by W. Bul- them were freshwater species (Kahl, 1931, p. lington (1939) clearly indicates that the latter scien- 317). He recommended to accept F. vernalis as tists dealt with the absolutely different ciliate species. a distinctive species name because the ciliate First of all, Ehrenberg (1833, 1838) personally contained zoochlorellae (which could not be expe- worked with the freshwater “green” ciliates (conta- rimentally kept in F. leucas) and used a different type ining numerous green “albuminous” particles in the of food (particularly diatoms). Unfortunately, he cytoplasm) that he collected repeatedly near Berlin did not make a redescription of this green Frontonia. in 1832, 1833, and 1835. He also just mentioned A. Kahl not only proposed to accept F. vernalis as (Ehrenberg, 1838) that some, probably similar but a separate species, but also indicated 2 ‘types’ of not identical, organisms were found by O. Müller such ciliates that differed from each other by the and J.B. Bory in the marine environment near cell shape. Copenhagen and Cadix. Moreover, he made a The situation was briefly recorded by W. Fois- clear statement: “I have no rights to combine them sner who wrote 2 decades ago that “status (of green into one” (Ehrenberg, 1838, p. 329). Bullington, frontoniid) is not yet clear” (Foissner et al., 1999, apparently, could not translate the German text p. 416). He also highlighted the similarity of oral properly and therefore started his description in kinetom in F. leucas and F. vernalis (“green F. leu- a wrong way: “Ehrenberg (1838) found a ciliate cas”) and remarked that “whether the chlorotic which he described under the name Bursaria, sub- populations are conspecific with the apochlorotic genus Frontonia (vernalis) in sea water near Berlin, ones needs detailed investigations” (Foissner et al., Copenhagen, and Cadix” (Bullington, 1939, p. 36). 1999, p. 423). This comment is of special importance Further he wrote: “…Parophrys fusca (Quennerstedt, because earlier J. Dragesco indicated for “F. leucas” 1869) which seems to me undoubtedly belongs here” containing Chlorella sp. a different from the classical (Bullington, 1939, p. 36). So, definitely, Bullington’s F. leucas number of vestibular kineties (Dragesco “F. vernalis” should be treated as a brackishwater and Dragesco-Kerneis, 1986, p. 319). species related to F. fusca (Quennerstedt, 1869; Kahl, 1931; Fokin, 2008). In the same article, CURRENT TAXONOMY OF FRONTONIA VERNALIS Bullington also described F. oculiaris (Bullington, 1939, p. 42–46), which likewise reminds F. fusca. In all recently published molecular trees concer- Further on, in several recent publications the ning Frontonia, the 18S rRNA gene sequence with authors accepted those wrong descriptions of Bul- accession number U97110, which is shown in lington and until 2018 treated F. vernalis as a bra- GenBank database as F. vernalis, is present. This ckishwater species (Chen et al., 2014; Cai et al., sequence is the only one available for the species; 2018). Additionally, a redescription of “F. oculiaris” it was deposited by Hirt and the colleagues in 1997, was made (Pan et al., 2013b) which, according to but has not yet been supported by any publication. morphology and the sequences presented, is de- It is known that Hirt and his colleagues worked with finitely F. fusca (Fokin, 2008; Fokin et al., 2019). the freshwater frontoniid hosting Chlorella-like Moreover, the same researchers made another cytoplasmic symbionts (e.g. Berninger et al.,1986; redescription of F. canadensis as a brackishwater Finlay et al.,1987; Esteban et al., 2010), which was species (Pan et al., 2013a), not paying attention to collected in a small productive pond (Priest Pot, the important fact that in the original description Like District, Cumbria, England). It looks like (Roque and Puytorac, 1972) this species was cha- the identification of that ciliate as F. vernalis was racterized as a freshwater ciliate. It is especially done at that time by Dr. C. Curds (Berninger et al., Protistology · 39

1986, p. 557), and thereafter the ciliate was never At present, we have got at our disposal more characterized morphologically in the large set of than 70 sequences of the representatives of the the English-language publications where the name genus Frontonia. The composition of various groups “F. vernalis” was utilized (see: Esteban et al., 2010). in both freshwater and brackish sublinages of Meanwhile, this frontoniid does not match the Frontonia allows splitting the genus phylogenetically original morphotype of green F. vernalis described into 3 clusters (Fokin et al., 2019), most likely by Ehrenberg (1833, 1838) since there are two CVs vs corresponding to the generic level. Therefore, one in the cells from the UK population. So, several obviously, a comprehensive revision of the genus articles were published using in fact the unknown Frontonia is required, including segregation of a (i.e. not yet described) Frontonia sp. number of new genera, like it has already been done for several large ciliate taxa – for example, OUTLOOK spathidiids and dileptids (Foissner and Xu, 2007; Vdačnŷ and Foissner, 2012). The comparative analysis of some old and new publications dealing with taxonomy of the genus Frontonia regretfully witnesses for inattentive References reading or ignoring of the previously published literature by some protistologists of the past and Andreoli I., Fokin S.I., Verni F. and Petroni G. the present. 2007a. Phylogenetic relationships within fronto- As a result of comparison between the materials niids. J. Eukaryot. Microbiol. 54, 28S, Abstract 72A. from literature and own data, the author proposes Andreoli I., Fokin S.I., Verni F. and Petroni G. to reject F. vernalis as a valid species’ name and 2007b. Phylogenetic relationships within peniculine assume that this is a cluster of closely related fresh- ciliates and the paraphyly of Frontonia. Protisto- water ciliates with one contractile vacuole and a logy. 5,12, Abstract. stable ability to accommodate green algae as the Berninger U.G., Finlay B.J. and Canter H.M. cytoplasmic symbionts. One of such species was just 1986. The spatial distribution and ecology of zoo- recently described from the North of China – F. shii chlorellae-bearing ciliate in a productive pond. J. (Cai et al., 2018), and description of two others – F. Protozool. 33, 557–563. paravernalis and F. apovernalis (briefly mentioned in Bullington W.E. 1939. A study of spiraling in Fokin et al., 2017) is currently in progress. the ciliate Frontonia with a review of the genus and The green frontoniid used by the colleagues description of two new species. Arch. Protistenkd. from the UK (Finlay et al., 1987 and references 92, 10–66. therein) should be precisely described as a different Cai X., Wang Ch., Pan X., El-Serehy H.A., ciliate (for instance – F. pseudovernalis) using a Mu W., Gao F. and Qiu Z. 2018. Morphology and multidisciplinary approach. “F. vernalis” described systematics of two freshwater Frontonia species by Bullington (1939) has nothing in common with (Ciliophora, Peniculida) from northeastern China, the original description of Ehrenberg (1833, 1838) with comparisons among the freshwater Frontonia and most likely was a brackishwater ciliate similar spp. Europ. J. Protistol. 63, 105–116. to F. fusca (Fokin, 2008). Carey Ph.G. 1992. Marine Interstitial Ciliates. F. oculiaris, also described by Bullington (1939), An illustrated key. Chapman and Hall, London, was obviously F. fusca; therefore, the name F. New York. oculiaris should be considered as a younger synonym Chen Y., Zhao Y., Pan X., Song W., Al- of F. fusca. Thus, a redescription of F. oculiaris made Farraj S.A., Al-Rasheid K.A.S. and Qiu Z. 2014. by Pan with colleagues (Pan et al., 2013b) should Morphology and phylogeny of a new Frontonia cilia- be treated just as a morphological study of the local te, F. paramagna spec. nov. (Ciliophora, Peniculida) Chinese population of F. fusca. The redescription from Harbin, Northeast China. Zootaxa. 3827, of F. canadensis (Roque and Putorac, 1972) from 375–38. brackish waters made by the same authors (Pan et Claparède E. and Lachmann J. 1858. Etudes sur al., 2013b) should be considered as a description of lesinfusoires et les rhizopodes. Geneve. a new species that has nothing in common with the Corliss J.O. 1979. The Ciliated Protozoa. Cha- original description of a freshwater ciliate made in racterization, Classification, and Guide to the Lite- the 1970ies (Roque and Puytorac, 1972). rature, 2nd ed. Pergamon Press. 40 · Sergei I. Fokin

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Address for correspondence: Sergei I. Fokin. Department of Biology. Protistology-Zoology Unit. University of Pisa, 56126 Pisa, Italy; e-mail: [email protected].