Hemiholostichidae, Hong & Zhang & Pan & Jiang, 2025

Order Stichotrichida Fauré-Fremiet, 1961 View in CoL View at ENA

Familp Hemiholostichidae Vd’ačný & Foissner, 2021

Genus Psilotrichides Heber et al., 2018

Psilotrichides hawaiiensis Heber et al., 2018

( Fig. 7A–L; Table 2)

2018 Psilotrichides hawaiiensis Heber et al. , Journal of Eukaryotic Microbiology 65: p. 291.

2019 Psilotrichides hawaiiensis Luo et al. , BMC Evolutionary Biology 19: p. 125.

Voucher material: Two permanent voucher slides (registration no. ZZH2021040901/1–2), 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. PQ836550 as Psilotrichides hawaiiensis ).

Chinese population of Psilotrichides hawaiiensis : Body size 51–76 μm × 37–57 μm in vivo ( N = 5), 52–88 μm × 37–66 μm in protargol-stained specimens ( N = 18). Body in vivo semirigid, inverted-pyriform in shape, right margin S-shape curved, anterior end rounded or obliquely truncate, posterior end bluntly tapered ( Fig. 7A, D–F). Most cells dorsoventrally flatened ≤2:1, ventral side slightly protruding. Numerous colourless rod-shaped bacteria (~2.3 μm × 0.6 μm) residing on body surface ( Fig. 7B). Cytoplasm colourless, usually containing some lipid droplets, ~1–3 μm across. Numerous green algae (~5–13 μm), nearly spherical or tapered Euglenoid-like, with red eyespot, widespread throughout body, rendering cells greenish ( Fig. 7C, D). Some algae could be found in food vacuoles. Movements occasionally moderately fast, crawling on substrate, or mostly relatively slow, swimming by rotating around longitudinal axis of body. Cortex inflexible, colourless, lacking cortical granules.

Nuclear apparatus in or slightly lef of cell midline, composed of two elliptical macronuclear nodules (18 μm × 10 μm on average) and one global micronucleus (~7 μm across) in vivo attached to or near macronuclear nodules ( Fig. 7G, L). Contractile vacuole ~12 μm across in diastole, usually positioned at lef cell margin in midbody ( Fig. 7F) or slightly lef of midline (in one of five cells observed) ( Fig. 7E).

Adoral zone of membranelles terminates at 35%–50% of body length in vivo and at ~43% on average in protargol preparations, composed of 21–26 (on average 23) membranelles. Bases of longest membranelle ~7 μm long ( Fig. 7D, H, J), cilia ≤18 μm long in vivo ( Fig. 7A, D–F). Adoral zone question mark-like pattern in ventral view ( Fig. 7D). Undulating membranes roughly in Stylonychia patern, paroral slightly curved and almost parallel to shorter endoral membrane composed of monokinetids ( Fig. 7H, J, K).

Total number of cirri ranging from 16 to 30; arranged in four ventral rows, one postoral row, and one lef and one right marginal row. Cirral patern relatively simple, with large gaps between cirri making it difficult to determine the number in each row ( Fig 7H, J, K). All ventral rows twisting lef slightly. Ventral cirral row 1 (R1) composed of two or three cirri, with anteriormost cirrus near distal end of adoral zone; R2 typically containing two cirri, rarely three cirri; R3 containing two to seven cirri; and R4 containing two to eight cirri. Lef marginal row composed of two to five cirri, commencing at level of buccal vertex, terminating more or less subcaudally in most cells. Right marginal row composed of four to six cirri; anteriormost cirrus situated slightly behind anteriormost cirrus of R4. Two or three postoral ventral cirri located behind buccal vertex and well separated from rear end of adoral zone ( Fig. 7H, J, K). In vivo, all cirri thin and long, ~15 μm long ( Fig. 7A, D–F).

Dorsal bristles 3.0–4.5 μm long, arranged in three meridional rows. Tree dorsal kineties slightly shortened anteriorly, extending to rear body end ( Fig. 7E, I, L). Caudal cirri absent.

Phplogenetic analpses

( Fig. 1)

Te GenBank accession numbers, lengths, and GC content of two newly obtained SSU rDNA sequences are as follows: Pelagotrichidium faurei, PQ 846962, 1774 bp, 45.72%; Psilotrichides hawaiiensis, PQ 836550, 1773 bp, 45.63%. Pelagotrichidium faurei differs from Heterouroleptus weishanensis (OR666141) by 12 nucleotides, which is the most similar sequence in the GenBank. Te Chinese population of Ps. hawaiiensis differs from the Guam population ( MK211834 View Materials ) by three nucleotides. In the phylogenetic tree based on SSU rDNA sequences, Pe. faurei branches with species of the family Strongylidiidae Fauré-Fremiet, 1961 with high support (89% ML,.99 BI), while the type genus Hypotrichidium of the family Spirofilidae nests within the oxytrichids. Te Chinese population of Ps. hawaiiensis clusters with the Guam population (89% ML,.89 BI), forming a sister group with Urospinula succisa (Müller, 1786) Esteban et al., 2001 and Hemiholosticha kahli Luo et al., 2019 with full support (100% ML, 1.00 BI). However, the positions of Pe. faurei and Ps. hawaiiensis are not robust owing to the low support values and partly incongruent topologies in the ML tree and BI tree.