Diplodinium anisacanthum, Cunha, 1914

Cedrola, Franciane, Dias, Roberto Júnio Pedroso, Martinele, Isabel & D’Agosto, Marta, 2017, Polymorphism and inconsistencies in the taxonomy of Diplodinium anisacanthum da Cunha, 1914 (Ciliophora, Entodiniomorphida, Ophryoscolecidae) and taxonomic notes on the genus Diplodinium Schuberg, 1888, Zootaxa 4306 (2), pp. 249-260 : 250-253

Morphology of Diplodinium anisacanthum

( Figure 1 ; Table 1)

The six Diplodinium anisacanthum morphotypes ( monacanthum , diacanthum , triacanthum , tetracanthum , pentacanthum and anisacanthum ) have an oval body, laterally compressed, and tapered posteriorly. Two retractable ciliary zones ( Figure 1 a), one adoral and one dorsal, at anterior end of body, separated by an inconspicuous operculum. Ectoplasm extendind beyond of the body and forms 1–6 caudal spines, according from morphotype ( Figure 1 d). Diplodinium anisacanthum morphotype monacanthum with one caudal spine; Diplodinium anisacanthum morphotype diacanthum two; Diplodinium anisacanthum morphotype triacanthum three; Diplodinium anisacanthum morphotype tetracanthum four; Diplodinium anisacanthum morphotype pentacanthum five and Diplodinium anisacanthum morphotype anisacanthum six ( Figure 1 e–j). Endoplasm with many food particles, essentially plant material. Macronucleus, rod-shaped, wide anteriorly, inclined about 90° towards ventral region ( Figure 1 b). The elliptical micronucleus is in a depression in the dorsal anterior surface of the macronucleus ( Figure 1 b). Two contractile vacuoles, each with a dorsally opening excretory pore ( Figure 1 a). Rectum is a small and tubular structure located in the posterior end of the body, where cytoproct opens ( Figure 1 a).

Oral infraciliature corresponding to the Diplodinium-type ( Ito & Imai 2006) ( Figure 1 e–j). This pattern consists of an adoral polybrachykinety (AP), vestibular polybrachykinety (VP), a dorsal polybrachykinety (DP) and paralabial kineties (PK). AP involves the buccal opening; VP is long and extends into vestibule, if originating internally by the dorsal side of AP. DP extending laterally along dorsal anterior side of the body. Four or five PK close to ventral portion of AP. All D. anisacanthum morphotypes show the same pattern and organization of infraciliary bands ( Figure 1 c).

Diplodinium anisacanthum was described by da Cunha (1914) from Brazilian cattle and sheep. Dogiel (1927), in his monograph of family Ophryoscolecidae renamed the species described by da Cunha (1914) as Diplodinium (Anoplodinium) denticulatum f. anisacanthum , and described six other subspecies that differed from the first in the number of caudal spines [ D. (Anoplodinium) denticulatum f. anacanthum , D. (Anoplodinium) denticulatum f. monacanthum , D. (Anoplodinium) denticulatum f. diacanthum , D. (Anoplodinium) denticulatum f. triacanthum , D. (Anoplodinium) denticulatum f. tetracanthum and D. (Anoplodinium) denticulatum f. pentacanthum )]. Kofoid & MacLennan (1932) in their Diplodinium taxonomic review, raised to the species level the subspecies proposed by Dogiel, using the following names: D. anisacanthum , D. anacanthum , D. monacanthum , D. diacanthum , D. triacanthum , D. tetracanthum and D. pentacanthum . Latteur (1970) considered Diplodinium anisacanthum as a species with polymorphisms [ D. anisacanthum f. anacanthum , D. anisacanthum f. monacanthum , D. anisacanthum f. diacanthum , D. anisacanthum f. triacanthum , D. anisacanthum f. tetracanthum , D. anisacanthum f. pentacanthum and D. anisacanthum f. anisacanthum ]. Hence, due to the different taxonomic interpretations of the features of the posterior end of the body, Diplodinium anisacanthum morphotypes are regarded as a polymorphic species and classified as subspecific level (Imai et al. 1981; Shimizu et al. 1983; Ito et al. 1994; Guirong et al. 2000; Gurung et al. 2002; Booyse & Dehority 2011; Booyse et al. 2014), or as seven species ( Kofoid & Christenson 1933; Dehority 1979; 1986; Clarke 1964; Baraka 2012).

Although those Diplodinium ciliates have been elevated to the species level by Kofoid & MacLennan (1932), the possibility of being a single, polymorphic species raised by Dogiel (1927) and later by Latteur (1970), is considerable, because the morphotypes are almost identical, differing only in the number of caudal spines ( Figure 1 ; Table 1).

According to the International Code of Zoological Nomenclature (ICZN, 1999) different Diplodinium anisacanthum morphotypes should be classified as subspecies, since they were described before 1960. Thus, in this study we propose to rename them: Diplodinium anisacanthum monacanthum , Diplodinium anisacanthum diacanthum , Diplodinium anisacanthum triacanthum , Diplodinium anisacanthum tetracanthum , Diplodinium anisacanthum pentancanthum and Diplodinium anisacanthum anisacanthum .

Caudal projections are used as species diagnostic feature in family Ophryoscolecidae by several authors following the taxonomic classification proposed by Kofoid & MacLennan (1932) ( Kofoid & Christenson 1933; Dehority 1979; 1986; Clarke 1964; Baraka 2012). However, according Latteur (1966; 1970) many species of ophryoscolecid ciliates present considerable polymorphism and this profoundly influences the morphology of the posterior end of the body. Latteur (1966; 1970) suggests that variations in caudal projections should not be used in the species diagnosis in family Ophryoscolecidae because often constitute intraspecific variation.

Polymorphism in ophryoscolecid ciliates was reported by some authors and to be influenced by factors such as interactions between the ciliates, especially those of predation and cannibalism ( Poljansky & Strelkow 1938; Latteur 1966; Martinele & D'Agosto 2008). Williams & Coleman (1992) reported that in monoclonal cultures, spines in Diplodinium pentacanthum gradually become smaller, tending to disappear, suggesting that environmental factors possibly determine the presence and number of caudal projections.

Williams & Coleman (1992) observed that caudal projections in Entodinium caudatum Stein, 1858 are lost in monoclonal cultures. However, the insertion of Entodinium bursa Stein, 1858 in the culture promotes the emergence of caudal projections in E. caudatum , which may be related to the fact that E. bursa be the main predator of E. caudatum . The author suggests that the presence of the spine decreases predation, whereas E. bursa engulfs E. caudatum by the posterior region, thus the spine difficults the process.

Imai et al. (2002) studied transfaunation processes and establishment of Diplodinium rangiferi Dogiel, 1925 between wild ruminants ( Cervus nippon centralis Kishida, 1936 ) and domestic cattle ( Bos taurus L.). Inoculate specimens of D. rangiferi without caudal spines for the rumen of deer for the rumen of calves, after two weeks of inoculation, noticed the presence of D. rangiferi with caudal projections in calves.

There is no information on how polymorphism of Diplodinium anisacanthum correlates to molecular data, since there are only two sequences of this species available in the GenBank database.

Figures

FIGURE 1. Six morphotypes of Diplodinium anisacanthum da Cunha, 1914 reported in Brazilian sheep (Ovis aries L.) a. D. anisacanthum anisacanthum, schematic drawing based on specimen stained with Lugol’s solution; b – d: schematic drawings of nuclear apparatus (b), infraciliary bands (c) and caudal projections (d). e – j. specimens after silver carbonate impregnation. e. D. anisacanthum monacanthum; f. D. anisacanthum diacanthum; g. D. anisacanthum triacanthum; h. D. anisacanthum tetracanthum; i. D. anisacanthum pentacanthum; j. D. anisacanthum anisacanthum. AP: adoral polybracykynety; ACZ: adoral ciliary zone; CS: caudal spine; Ctp: cytoproct; CV: contractile vacuole; DCZ: dorsal ciliary zone; DP: dorsal polybrachykynety; Ma: macronucleus; Mi: micronucleus; VP: vestibular polybrachykynety. Bars: 20 µm.