Tintinnopsis fimbriata Meunier, 1919

Jung, Ji Hye Moon and Jae-Ho, 2025, Morphology and molecular phylogeny of controversial tintinnids Tintinnopsis fimbriata and T. uruguayensis (Protozoa: Ciliophora) collected from coastal waters of South Korea, Journal of Species Research 14 (1), pp. 86-95 : 88-91

Tintinnopsis fimbriata Meunier, 1919

( Table 1, Figs. 1 , 2 , 5 ) ḏêḝẖŀflệ (ṵḡ)

Tintinnopsis fimbriata Meunier, 1919: 31 , pl. 22, figs. 38, 39; Hofker, 1931: 321, fig. 5; Agatha, 2008: 261-272, figs. 1-3.

Tintinnopsis sp. Brandt, 1906: 16, pl. 17, figs. 5, 7, pl. 18, fig. 10; Brandt, 1907: 180.

Tintinnopsis meunieri Kofoid and Campbell, 1929: 40 , fig. 59.

Codonaria fimbriata Balech, 1948: 15 , pl. 6, figs. 69-86.

Material examined. Marine water, collected from Gomso Port , Jinseo-myeon , Buan-gun, Jeonbuk-do, Republic of Korea (35°35 ʹ 08 ʺ N, 126°36 ʹ 20 ʺ E) on 20 May 2021 .

Description (n = 7). Lorica 61-71 × 34-41 μm (on average 64.4 × 38.1 μm) in size, agglutinated, composed of obconical collar and globular to ellipsoidal bowl with cylindrical posterior process ( Figs. 1A- E , 2A- F ). Collar 7.0-10.5 μm (on average 8.6 μm) high, crown-shaped, with irregular rim; inner constriction 28-32 μm (on average 30.4 μm) in diameter. Ratio of lorica length to opening of collar diameter 1.6-1.8: 1 (on average 1.7: 1). Bowl occupies about 66% of lorica length, 33-37 μm (on average 34.4 μm) in diameter; end of bowl 61-86° (on average 72.3°) angle ( Figs. 1A , 2A- C ). Posterior process 11-15 × 6.0-8.5 μm (on average 12.0 × 7.6 μm) in size, with usually obliquely truncate open end ( Figs. 1A, B , 2A- C, E, F ). Closing apparatus present, agglutinated with small particles ( Figs. 1B , 2D ).

Habitat. Marine.

Distribution. Nieuwpoort in Belgium ( Meunier, 1919), Zuiderzee in the Netherlands ( Hofker, 1931), Elbmündung, the Kiel Canal, and coastal waters of Sylt in Germany ( Brandt, 1907; Kofoid and Campbell, 1929; Agatha, 2008), Atlántida in Uruguay ( Balech, 1948), Fort Pierce in the United States of America ( Strüder-Kypke and Lynn, 2003), and near Gomso Port in Korea (present study).

Phylogenetic analyses. The SSU rDNA- ITS1- 5.8S rDNA- ITS2-partial LSU rDNA sequence of Tintinnopsis fimbriata is 2,122 base pairs long with a GC content of 47.5% (GenBank accession no: PQ650933). The SSU rDNA sequence of the Korean population of T. fimbriata shows an identity of 96.25% (54 nucleotide differences) to the American population ( AY143560 ), which is the only available sequence and does not cluster together in the phylogenetic tree ( Fig. 5 ). The gene sequence rather clusters together with Stenosemella steini .

Additionally, the Korean SSU rDNA sequence of Tintinnopsis fimbriata is identical to those of the two American ( EU399542 , JN831838 ) and Chinese ( MT435075 ) populations of T. uruguayensis ( Fig. 5 ), but there are two nucleotide differences between the Korean populations of T. fimbriata and T. uruguayensis (GenBank accession No. PQ650934, this study). Furthermore, the ITS1, 5.8S rDNA, and ITS2 sequence of T. fimbriata shows identities of 99.76% (one nucleotide difference) to the Korean population and 99.53% (two nucleotide differences) to the Chinese population ( MT435062 ) of T. uruguayensis .

Remarks. Among the three congeners sharing similar lorica morphology, Tintinnopsis amoyensis is easily distinguished from the Korean T. fimbriata by its smaller size (45-50 × 25-27 μm vs. 61-71 × 34-41 μm) ( Nie, 1934). Tintinnopsis uruguayensis differs from T. fimbriata by the slender lorica (ratio of lorica length to opening of collar diameter: 1.6-2.7 vs. 1.3-1.8) ( Meunier, 1919; Balech, 1948; Agatha, 2008; Bai et al., 2020; this study).

The Korean specimens of T. fimbriata match the dimensions estimated from the original illustrations in terms of the lorica shape and size (61-71 × 34-41 μm vs. 68- 75 × 52-54 μm) ( Meunier, 1919) ( Table 1). However, in terms of the collar width, the Korean population does not match closely with the original population (34-41 μm vs. 52-54 μm) but corresponds more closely to the neotype (38-56 μm vs. 34-41 μm) ( Agatha, 2008).

As noted above, the Korean population of T. fimbriata is morphologically consistent with the neotype ( Table 1). However, the sequence of the neotype is unavailable, and sequence AY143560 (assigned to T. fimbriata ) is presumed to have been derived from a misidentified specimen due to the unclear posterior process of the lorica ( Strüder-Kypke and Lynn, 2003; Agatha, 2008). Even though the Chinese population of T. uruguayensis differs from the neotype of T. fimbriata in the infraciliature pattern (left ciliary field: 4-6 vs. 6-8; lateral ciliary field: 11-14 vs. 9-16) ( Agatha, 2008; Bai et al., 2020), it is challenging to definitively reject their conspecificity due to the unavailability of the SSU rDNA sequence for the neotype.

The identical SSU rDNA sequences between congeners are well-documented in some ciliates (e.g., Tetrahymena , Parafavella ) and this may be one such case ( Lynn and Strüder-Kypke, 2006; Jung et al., 2018). Therefore, there is no doubt that an in-depth taxonomic discussion between T. fimbriata and T. uruguayensis is necessary. When focusing on the key character of collar opening diameter, T. fimbriata and T. uruguayensis observed in this study are clearly distinguishable ( Fig. 6 ). However, when including the original, neotype, and Chinese populations of T. uruguayensis in the comparison, the measurements overlapped within the range of 23-56 μm, making it difficult to determine their relationships.

When comparing these populations separately based on Table 1, the morphology of T. fimbriata and T. uruguayensis from Korea does not overlap, and differences in their sequences also suggest they are distinct species. Moreover, the collar opening diameter of T. uruguayensis reported by Strüder-Kypke and Lynn (2008) appears to differ significantly from that mentioned in the original description (40-50 μm vs. 22-27 μm) but is more similar to those in the original description of T. fimbriata (40-50 μm vs. 52- 54 μm), raising the possibility of misidentification.

To address these issues, we performed molecular analyses, but the commonly used genetic markers did not provide clear differentiation, and the analysis of markers with higher discriminatory power was unsuccessful (e.g., CO1). Based on the observed differences between the two Korean species, we identified them as more similar species com- pared to the original or neotype descriptions. Therefore, it is important to recognize the challenges, posed by lorica variation and genetic conservation, in future studies. Additionally, further research utilizing genetic markers capable of precisely identifying T. fimbriata and T. uruguayensis is needed.

Voucher specimens. The three slides were deposited at the National Marine Biodiversity Institute of Korea ( MABIK PR00045100- MABIK PR00045102).

Figures

Fig. 1. Tintinnopsis fimbriata from a Bouin’s fluid-fixed sample. A, C-E, Lateral views of the loricae, arrowheads marking boundary between the collar and the bowl, arrows indicating the borderline between the bowl and the posterior process; B, Optical section of the middle of the cell inside the lorica, arrow showing the closing apparatus and arrowhead indicating the estimated attachment point on the inner surface of lorica. The same scale is applied for comparison of size variation(A, B; C-E). Scale bars:A, C=30 μm.

Fig. 2. Tintinnopsis fimbriata, isolated from a Bouin’s fluid-fixed sample, under a scanning electron microscope. A-C, Lateral views of the loricae; D-F, Anterior and posterior ends of the loricae, arrow indicating the attachment point between the inner surface of the collar and the closing apparatus.The closing apparatus was constructed by finer particles than those on the lorica (D). The same scale is applied for comparison of size variation(A-C; E, F). Scale bars:A=30 μm, D=20 μm, E=10 μm.

Fig. 5. Bayesian inference(BI) tree based on SSU rDNA sequences, showing the phylogenetic position of Tintinnopsis fimbriata and T. uruguayensis. Newly obtained sequences are in bold. GenBank accession numbers follow species names. Numbers at the nodes represent the Bayesian inference (BI) posterior probabilities and the maximum likelihood (ML) bootstrap values (solid circles=full supporting values). Dashes indicate posterior probabilities<0.5, bootstrap values<50%, or different topologies in BI and ML phylogenies. The scale bar represents three nucleotide substitutions per 100 nucleotides.

Fig. 6. Morphological differences between Tintinnopsis fimbriata and T. uruguayensis. A, Box plots showing differences in collar opening diameter; B, Box plots showing differences in the ratio of lorica length to collar opening diameter.