Typification of the genus Dileptus Dujardin, 1841 (Ciliophora, Rhynchostomatia).

In their monograph of the dileptids, Vďačný and Foissner (2012) could not clarify the type species of the genus DileptusDujardin, 1841. Thus, they suggested that the problem be referred to the International Commission on Zoological Nomenclature. However, recently we discovered that Dujardin (1841) has originally typified Dileptus with Amphileptus anser sensu Ehrenberg (1838) which is in fact a misidentified Amphileptus margaritiferEhrenberg, 1833, a common species also originally classified in Dileptus. Under Article 70.3.2 of the Code, Dileptus margaritifer (Ehrenberg, 1833) Dujardin, 1841, thoroughly redescribed by Foissner et al. (1995), is now the type of Dileptus. This has the great advantages of historical continuity and that new combinations (names) are not required.

Introduction

The type concept caused great progress in the nomenclature of organisms (for a review, see Richter 1948). According to the International Code of Zoological Nomenclature (ICZN 1999, Article 61), each nominal taxon in the family, genus or species group has actually or potentially a name-bearing type. This provides the objective standard of reference for the scientific name. However, typification is sometimes difficult, especially for long-known taxa, e.g., for the ciliate genus Dileptus established by Dujardin (1841). This is only one of many unsolved cases as noted by Aescht, 2001, Aescht, 2008, Berger, 1999, Berger, 2001, and Foissner (2002).

Vďačný and Foissner (2012, p. 266) described the type species problem in Dileptus as follows: “Dujardin (1841) established the genus Dileptus with three nominal species: Dileptus anser (a misidentified D. margaritifer), D. folium (now Litonotus cygnus), and “Dileptus (Amphileptus margaritifer, Ehr. Infus. Pl XXXVII, fig. 5: 355)”, adopting the description from Ehrenberg (1838). He did not fix a type species. This was done by Fromentel (1875), using D. folium. Kahl (1931) overlooked Fromentel's typification and synonymized D. folium with Litonotus cygnus. Further, in his characterization of Dileptus on page 205, Kahl (1931) stated “typical species: D. anser”. Dragesco (1963) and Jankowski (1967) followed. However, under the Code, D. anser cannot be considered as type species of Dileptus because (i) the first author who subsequently designates one of the originally included nominal species validly designates the type species of that genus or subgenus (type by subsequent designation), and no later designation is valid (Article 69.1 of the ICZN 1999), and (ii) the term “designation” in relation to fixation of a type species [Arts. 68, 69] must be rigidly construed (Article 67.5 of the ICZN 1999). Thus, D. folium is the validly fixed type species of Dileptus, according to Articles 67.1.2 and 69.1 of the ICZN (1999). Unfortunately, D. folium is a junior synonym of Litonotus cygnus, a pleurostomatid ciliate belonging now to a different subclass, Haptoria (Vďačný et al. 2011). Thus, recognition of Fromentel's forgotten typification would cause changes in many well established ciliate names. Therefore, we shall bid the International Commission on Zoological Nomenclature to use its plenary power (i) to suppress Fromentel's (1875) typification of Dileptus, and (ii) to fix D. margaritifer as the type species of Dileptus because it is a well-known species (see description below), matching Jankowski's characterization of Dileptus and having slides deposited in an international repository”.

This exhaustive description of the type species problem demonstrates the complex situation in Dileptus. Fortunately, we discovered – by the studies of the little known books by Pritchard, 1852, Pritchard, 1861 – that Dujardin (1841) has fixed the type of Dileptus by original designation. Here we explain the history of Dileptus and its type species in the light of these “new” findings.

Results and Discussion

Brief history of Dileptus and Dileptus margaritifer

To explain the complex situation, we provide synonymies for Dileptus and its type species. The lists contain only entries, which are important for the explanation of the type species problem (see below). For more detailed lists, improved diagnoses, derivation of names, a comment on type and voucher material, and a comprehensive description, see Vďačný and Foissner (2012).

Dileptus Dujardin, 1841

Dileptus margaritifer (Ehrenberg, 1833) Dujardin, 1841

Up to now, it was generally assumed that Dujardin (1841) established Dileptus without fixing a type species (see “Introduction”). To eradicate this flaw, three species have been proposed as type (basionyms given), namely Dileptus folium Dujardin, 1841 by Fromentel (1875), Vibrio anser Müller, 1773 by Kahl (1931), and Amphileptus margaritifer Ehrenberg, 1833 by Vďačný and Foissner (2012).

Locating the original designation of the type species in. During the studies of Pritchard, 1852, Pritchard, 1861 little-known reviews, we recently discovered that Dujardin has made a typification: “The Amphileptus anser is taken by Dujardin as the type of a genus termed Dileptus, and A. meleagris of a genus Loxophyllum.” and “The type of this genus Dileptus is the Amphileptus anser of Ehrenberg; and the A. margaritifer (Ehr.) is referable also to it” (Pritchard 1852, p. 587, 591). Unfortunately, Dujardin (1841) did not designate the type (Amphileptus anser sensu Ehrenberg) in the Dileptus section on pages 404–410, but in the Amphileptus section on page 484 (see list of synonyms of D. margaritifer). Likely for that reason, all later workers, except for Pritchard, overlooked the type fixation. In spite of that, Amphileptus anser sensu Ehrenberg (1838) is type of Dileptus by original designation, and all later fixations are invalid (ICZN 1999, Article 70.2).

sensu Ehrenberg (1838) is synonymous with() Dujardin, 1841. Dileptus anser (Müller, 1773) Dujardin, 1841 – basionym Vibrio anser, now Pseudomonilicaryon anser (Müller, 1773) Vďačný and Foissner, 2012 – is a highly characteristic species with a very long and highly motile proboscis already described and illustrated by Müller, 1773, Müller, 1786, Figs 11–14; for monographic treatment, see Vďačný and Foissner 2012, p. 359). It is clearly different from the Amphileptus anser population described and illustrated by Ehrenberg (1838, Figs 7–10), which is very likely synonymous with D. margaritifer, as already proposed by Kahl (1931), Dragesco (1963), and Wirnsberger et al. (1984). By mistake, Vďačný and Foissner (2012, p. 359, 363) assigned A. anser sensu Ehrenberg (1838, Figs 7–10) to Pseudomonilicaryon anser (see list of synonyms). In the absence of type and voucher material, the identifications by Ehrenberg (1838) cannot be verified, but there is clear evidence that Ehrenberg's Amphileptus margaritifer (Figs 1–6) and A. anser (Figs 7–10) are identical.

Figs 1–14

Dileptus margaritifer (1–6) and D. anser (7–10) according to Ehrenberg (1838) and D. anser (11–14) according to Müller (1786). Scale bar 100 μm. CV – contractile vacuoles, OO – oral opening.

The discussion demonstrates that Dujardin (1841) fixed a misidentified species as type of Dileptus, suggesting that Article 70.3 of the ICZN (1999) can be applied and Dileptus margaritifer can be chosen as type of Dileptus.

Application of Article 70.3 of the. Article 70.3 of the Code states: “If an author discovers that a type species was misidentified, the author may select, and thereby fix as type species, the species that will, in his or her judgement, best serve stability and universality, either 70.3.1. the nominal species previously cited as type species, or 70.3.2. the taxonomic species actually involved in the misidentification. If the latter choice is made, the author must refer to this Article and cite together both the name previously cited as type species and the name of the species selected.”

This means that we can select between Vibrio anser Müller, 1773 (Article 70.3.1) and Amphileptus margaritifer Ehrenberg, 1833 (Article 70.3.2) because both species were originally included in Dileptus Dujardin, 1841 (Article 67.2).

With reference to Article 70.3.2 of the Code, the type species of Dileptus Dujardin, 1841 is now fixed as Dileptus margaritifer (Ehrenberg, 1833) Dujardin, 1841 (basionym Amphileptus margaritifer); in the original description of Dileptus, Dujardin (1841) fixed the synonymous Amphileptus anser sensu Ehrenberg (1838) as type species, a misidentified population as already proposed by previous monographers (Dragesco, 1963, Kahl, 1931, Wirnsberger et al., 1984). Of course, Dileptus margaritifer is also the type species of the nominotypical subgenus Dileptus (Dileptus) Dujardin, 1841 (Jankowski 1967).

We apply Article 70.3.2 because this serves best the spirit of the Code, i.e., stability and universality especially because no name changes are required. Further, D. margaritifer is well known and voucher slides have been deposited in a renowned repository, the Biologiezentrum of the Oberösterreichischen Landesmuseum in Linz (LI), Upper Austria (Aescht, 2008, Vďačný and Foissner, 2012).

1841	Dileptus – Dujardin, Zoophytes, p. 404, 484 (original description, including type fixation). Type species (by original designation on p. 484): Dileptus margaritifer (Ehrenberg, 1833) Dujardin, 1841 (basionym Amphileptus margaritifer Ehrenberg, 1833). For detailed explanation, see below.
1852	Dileptus – Pritchard, History of Infusorial Animalcules, p. 587, 591 (revision; note on type fixation by Dujardin 1841).
1861	Dileptus – Pritchard, History of Infusoria, p. 636, 638, 639 (revision; note on type fixation by Dujardin 1841).
1875	Dileptus – Fromentel, Études Microzoaires, p. 176, 177 (revision; invalid fixation of Dileptus folium Dujardin, 1841 as type species of Dileptus by subsequent designation).
1931	DileptusDujardin, 1841 – Kahl, Tierwelt Dtl., 21: 204 (revision; mentions Dileptus anser (Müller, 1773) Dujardin, 1841 as type species of Dileptus).
1963	DileptusDujardin, 1841 – Dragesco, Bull. biol. Fr. Belg., 97: 103 (revision; mentions Dileptus anser (Müller, 1773) Dujardin, 1841 as type species of Dileptus).
1967	DileptusDuj., 1840 – Jankowski, Mater. IV Konf. uč. Sekc. zool., year 1967: 36 (split of genus; mentions Dileptus anser (Müller, 1773) Dujardin, 1841 as type species of Dileptus).
2012	DileptusDujardin, 1841 – Vďačný and Foissner, Denisia, 31: 265 (detailed revision; suggest to fix A. margaritifer Ehrenberg, 1833 as type species of Dileptus under the plenary power of the International Commission on Zoological Nomenclature).

1833	Amphileptus margaritifer – Ehrenberg, Abh. dt. Akad. Wiss. Berl., year 1833: 230 (original description without illustration).
1838	Amphileptus anser – Ehrenberg, Infusionthierchen, p. 355, Tafel XXXVII, Fig. IV (Figs 7–10 in present paper; misidentification; used as type of Dileptus by Dujardin 1841).
1838	Amphileptus margaritifer – Ehrenberg, Infusionsthierchen, p. 355, Tafel XXXVII, Fig. V (Figs 1–6 in present paper; revision and first illustration).
1841	Dileptus Amphileptus margaritifer, Ehr. – Dujardin, Zoophytes, p. 404 (combination with Dileptus).
1841	… séparer des Amphileptes de M. Ehrenberg, sonA. anserpour en faire le type de notre genre Dilepte (Voyez pag. 404–409) – Dujardin, Zoophytes, p. 484 (original designation of Amphileptus anser sensu Ehrenberg as type of Dileptus; for detailed explanation, see below).
1931	Dileptus (Vibrio) anser(O.F. Müller, 1786) – Kahl, Tierwelt Dt., 21: 205 (revision, misidentification).
1984	Dileptus margaritiferEhrenberg, 1838 – Wirnsberger, Foissner and Adam, Arch. Protistenk., 128: 314 (incorrect authorship; comparison with Dileptus anser, now Pseudomonilicaryon anser (Müller, 1773)).
1995	Dileptus margaritifer(Ehrenberg, 1833) Dujardin, 1841 – Foissner, Berger, Blatterer and Kohmann, Informationsberichte des Bayer. Landesamtes für Wasserwirtschaft, 1/95: 185 (ecological and morphological monograph and detailed description of African population; deposition of voucher material).
2012	Dileptus margaritifer(Ehrenberg, 1833) Dujardin, 1841 – Vďačný and Foissner, Denisia, 31: 292, Fig. 91a–r, 92a–z, 93a–k, 94a–z, 95a–w (Figs 1–6 in present paper; detailed revision; suggest to fix D. margaritifer as type species of Dileptus).
2012	Pseudomonilicaryon anser(Mueller, 1773) nov. comb. – Vďačný and Foissner, Denisia, 31: 359, pro parte, Fig. 112a–d, not Fig. 111a–t, 112e–v, 113a–r, 114a–g (Figs 7–10 in present paper; assigned, obviously par lapsus, Amphileptus anser sensu Ehrenberg to Pseudomonilicaryon anser; see below).