Pelagotrichidium faurei ( Tuffrau, 1972 ) Jankowski, 1978

Hong, Meijie, Zhang, Zihui, Pan, Hongbo & Jiang, Jiamei, 2025, Taxonomy and phylogeny of two planktonic hypotrichs, with establishment of a new family Pelagotrichidiidae (Protista: Ciliophora: Hypotrichia), Zoological Journal of the Linnean Society (zlaf 061) 204 (3), pp. 1-16 : 4-6

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scientific name	Pelagotrichidium faurei ( Tuffrau, 1972 ) Jankowski, 1978
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Pelagotrichidium faurei ( Tuffrau, 1972) Jankowski, 1978

1970 Hypotrichidium faurei Tuffrau , Journal of Protozoology 17: p. 38 ( nomen nudum).

1972 Hypotrichidium faurei Tuffrau, Protistologica 8: p. 260 (original description).

1978 Pelagotrichidium faurei Tuffarau–Jankowski, Tezisky Doklady Zoologischeski Institut Akademia NAUK SSSR : p. 40.

1999 Pelagotrichidium faurei Foissner et al. , Munich: Bavarian State Office of Water Management: p. 683.

Improved diagnosis (based on original description and present work): Body size 131–280 μm × 63–107 μm in vivo. Shape inverted pyriform, with a short ‘tail’. Cortical granules colourless, scatered across both cell sides.Adoral zone ~50% of body length, 42–73 membranelles. Contractile vacuole near lef cell margin, slightly above midway along cell length. Frontoventral rows usually five, two long and three short. Dorsal kineties usually five, including two dorsomarginal kineties. Two macronuclear nodules; one to four micronuclei. Freshwater habitat.

Type locality: Tuffrau (1972) collected the species from a pond in Yveline near Paris, France.

Etymology: Te name is in honour of Professor Fauré-Fremiet, in recognition of his outstanding contribution to Ciliatology.

Voucher material: No record of type material could be found. Twelve voucher slides (registration no. ZZH2021091701/1–5, ZZH2021110301/1–7), with many protargol-impregnated specimens, are deposited in the Laboratory of Protozoology, Ocean University of China. Pertinent specimens are circled in black ink on the coverglass. Te SSU rDNA sequence from the Chinese population has been deposited in GenBank (accession no. PQ846962 as Pelagotrichidium faurei ).

Remarks: Tis species was initially mentioned without a diagnosis in a summary published in the Journal of Protozoology Supplements ( Tuffrau1970), priortoitsformalestablishmentbyTuffrau (1972). Subsequently, Jankowski (1978) moved the species from the genus Hypotrichidium Ilowaisky, 1921 to the genus Pelagotrichidium Jankowski, 1978 , and designated it as the type species.

Description of the Chinese populations

( Figs 2–6 View Figure 2 View Figure 3 View Figure 4 View Figure 5 View Figure 6 ; Table 1 View Table 1 )

Te two populations exhibit similarities in the main morphological features, with the exception of body size.

Population I: Sized 131–155 μm × 63–94 μm in vivo ( N = 5) and 81–248 μm × 46–137 μm afer protargol staining ( N = 34). Te stained specimens appear significantly larger than the living cells, probably owing to the limited number of in vivo measurements, which might have excluded the largest individuals. Additionally, the use of a relatively high concentration and larger volume of bleaching solution during staining probably caused considerable cell expansion. A similar inflation effect was observed in the stained specimens of population II. Te remaining morphometric data of population I are listed in Table 1 View Table 1 . Te following description is based on population II.

Population II: 155–199 μm × 77–107 μm in vivo ( N = 5), 167–338 μm × 100–196 μm afer protargol staining ( N = 21); inverted pyriform shaped, anterior end broadly rounded, posterior end conspicuous apiculus or blunt tapered (two of five cells observed) ( Figs 2A, B, G View Figure 2 , 3A, B View Figure 3 ). Cell more or less flexible, not contractile. Cytoplasm colourless, filled with food vacuoles containing numerous green algae and diatoms, body dark grey and opaque ( Figs 2A–C, F, G View Figure 2 , 3B View Figure 3 ). Contractile vacuole located near lef margin, slightly above middle level of cell, ~19 μm in diameter in diastole state ( Figs 2C View Figure 2 , 3A View Figure 3 ). Colourless cortical granules, scatered irregularly in cortex,.5–1.0 μm in diameter ( Figs 2D View Figure 2 , 3E View Figure 3 ). Two ellipsoidal macronuclear nodules adjacent to each other, 39–63 μm × 21–45 μm afer protargol staining. One to four spherical micronuclei, ~6–10 μm in diameter ( Figs 2E, H, I View Figure 2 , 3D View Figure 3 ). Movement moderately fast, usually swimming by rotation around longitudinal axis of body.

Adoral zone occupies on average 50% of body length, composed of 42–73 membranelles, cilia ~23 μm long, distal end curving across the anterior cell margin on dorsal side and extending down right margin to ventral side (DE-value, the distance between the anterior body end and the distal end of adoral zone divided by the length of adoral zone of membranelles,.23 on average). Buccal cavity large and rather deep ( Figs 2H, I View Figure 2 , 3A, C View Figure 3 ). Undulating membranes roughly in Stylonychia patern, paroral almost parallel to endoral membrane and nearly equal in length, gently curving to the lef, ultimately intersecting optically with later near posterior end ( Figs 3F View Figure 3 , 4A, D View Figure 4 ). However, cells ofen swell and flex afer staining, and nearly half of specimens present a middle intersection ( Figs 2H View Figure 2 , 3C View Figure 3 ). Cirral patern as shown in Fig. 3C, D View Figure 3 . All cirri ~18 μm long. Somatic ciliature all lefward-spiralling, mainly comprising two long frontoventral rows (FVR IV and V) and three short rows (FVR I–III, each composed of several cirri). FVR I composed of two to five cirri, located in frontal area; FVR II composed of three to seven cirri, posteriormost cirrus near anterior end of undulating membrane; FVR III composed of four to nine cirri, located right of anterior portion of paroral, slightly longer than FVR II; FVR IV and V composed of 28–47 and 33–53 cirri, respectively, commencing posterior to distal end of adoral zone, terminating near rear cell end ( Figs 2H View Figure 2 , 3A, C View Figure 3 ). In 19 observed protargol-stained specimens, one individual bearing six (two long and four short) FVRs, and one individual bearing seven (three long and four short) FVRs. Lef marginal row with 41–70 cirri, commencing slightly ahead of level of proximal end of adoral zone, spiralling lefwards towards posterior end (‘tail region’) on dorsal side ( Fig. 2H, I, L View Figure 2 ). Right marginal row with 34–58 cirri, commencing at approximately anterior 15% of body to near rear body end ( Figs 2H, I, L View Figure 2 , 3A, C View Figure 3 ).

Dorsal cilia ~3 μm long in vivo, usually arranged in five dorsal kineties (DKs). DK1 composed of 11–32 dikinetids, anterior end shortened, terminating at ~66% of body length; DK2 and DK3 composed of 20–50 and 26–43 dikinetids, respectively, spiralling lefwards to ventral side, terminating at ~80% of body length; dorsomarginal kineties 4 and 5 composed of 16–22 and 2–5 dikinetids, respectively, terminating before mid-body ( Figs 2H, I View Figure 2 , 3C, D View Figure 3 ). Among 18 observed protargol-stained specimens, four individuals bearing six dorsal kineties, and one individual bearing seven. Individuals with six or seven dorsal kineties, comprising four or five dorsal kineties and two dorsomarginal kineties.

Cell division of Pelagotrichidium faurei based on population II

( Figs 4–6 View Figure 4 View Figure 5 View Figure 6 )

Stomatogenesis: In a very early divider, the oral primordium of the opisthe occurs as a field of closely spaced basal bodies on the surface, which develops de novo posterior to the parental adoral membranelles along the FVR IV when the parental cirri remain intact ( Figs 4A, B View Figure 4 , 6A View Figure 6 ). Subsequently, the oral primordium enlarges and gives rise to the undulating membranes anlage (UMA, frontoventral anlage I) to the right. Several parental cirri in frontoventral row IV may be involved in this process ( Figs 4C View Figure 4 , 6B View Figure 6 ). New membranelles are formed in the anterior portion of the primordium and progress posteriorly ( Figs 4C–E, G View Figure 4 , 6B, E, H View Figure 6 ). During the following stages, the differentiation of the membranelles is completed, and the anterior end of the newly formed adoral zone bends to the right ( Figs 4I View Figure 4 , 5A View Figure 5 , 6K View Figure 6 ). Anlage I (UMA) generates the cirri in the frontoventral row I at the anterior end, and the other portion splits longitudinally into paroral and endoral membranes ( Figs 4H, I View Figure 4 , 5A View Figure 5 ). In the proter, the parental adoral membranelles are inherited. Anlage I is formed by the dedifferentiation of the parental undulating membranes ( Fig. 4G, H View Figure 4 ). It generates frontoventral row I, and new paroral and endoral membranes exactly like the anlage I in the opisthe ( Figs 4I View Figure 4 , 5A View Figure 5 , 6E, G View Figure 6 ).

Frontoventral rows: Basically, the frontoventral cirri originate from five streaks. As the oral primordium of the opisthe grows, five frontoventral anlagen (FVA I–V) are generated to its right ( Figs 4D, E View Figure 4 , 6C View Figure 6 ). Te parental cirri in FVR IV and V may contribute to the formation. At the same time, in the proter, FVA I is formed by the dedifferentiation of the parental undulating membranes, and FVA II–V develop intrakinetally within the parental FVR II–V, respectively ( Figs 4D, G View Figure 4 , 6E View Figure 6 ). In the opisthe, FVA I–III are formed from the oral primordium, and FVA IV and V probably both originate from the parental FVR V ( Figs 4D, G–I View Figure 4 , 6E View Figure 6 ). Subsequently, each FVA streak broadens and lengthens, breaks apart, and differentiates into cirri in both proter and opisthe ( Figs 4H, I View Figure 4 , 6G, H View Figure 6 ). Six anlagen occur occasionally ( Figs 4H View Figure 4 , 5C View Figure 5 , 6G View Figure 6 ). Anlagen I–V (or I–VI) develop into frontoventral rows I–V (or I–VI), respectively. Eventually, the divider starts to elongate, and the new ciliary structures move further apart as they migrate towards their final positions ( Figs 5A, C View Figure 5 , 6K View Figure 6 ).

Marginal cirral rows: In the early middle stage, several cirri at the anterior end and below the middle of the marginal cirral row dedifferentiate into two anlagen in each marginal row ( Figs 4G, H View Figure 4 , 6E View Figure 6 ). Later, the anlagen extend bidirectionally and begin to differentiate into new marginal cirri, and the parental marginal cirri are resorbed gradually ( Figs 4H, I View Figure 4 , 5A, C, D View Figure 5 , 6G, H, K View Figure 6 ).

Dorsal ciliature: Te anlagen initiate from the proliferation of several basal bodies in the central region of dorsal kineties 1–3 ( Figs 4D, F View Figure 4 , 6D View Figure 6 ). Subsequently, two anlagen are formed within each of the dorsal kineties 1–3, while the parental dorsal kineties 4 and 5 remain intact ( Figs 4H–J View Figure 4 , 6F View Figure 6 ). In the middle stage, two short anlagen (DK 4 and 5) appear near the anterior portion of the right marginal cirral primordia and move dorsally ( Figs 5A, B View Figure 5 , 6L View Figure 6 ). Tese anlagen expand through the proliferation of basal bodies and extend in both directions, eventually replacing the parental dorsomarginal kineties ( Figs 5C, D View Figure 5 , 6M View Figure 6 ). No caudal cirri are formed.

Nuclear apparatus: A replication band is present in each macronuclear nodule in the early stage of division ( Figs 4A, F View Figure 4 , 6A View Figure 6 ). In the middle late divider, two macronuclear nodules fuse into a single ellipsoidal mass, and several micronuclei also fuse into a single mass ( Figs 4J View Figure 4 , 6J View Figure 6 ). In the next stage, the macronucleus lengthens and splits, and the micronuclei divide mitotically ( Figs 5B View Figure 5 , 6K View Figure 6 ). Eventually, two macronuclear nodules and one to four micronuclei are formed in each daughter cell ( Fig. 5D View Figure 5 ).