Strongylidium wuhanense, Luo & Yan & Shao & Bourland & Song, 2018

STRONGYLIDIUM WUHANENSE SP. NOV.

( FIG. 5; TABLE 1)

urn:lsid:zoobank.org:act:6A330535-8F81-4766-9F0C-C3B4C1CE8E13

Diagnosis: Freshwater Strongylidium ; 135–200 μm × 40–60 μm in vivo; cell with a conspicuous tail; cortical granules colourless, spherical, ~1–1.5 μm across, irregularly distributed; adoral zone more or less bipartite, with approximately seven distal and 21 proximal membranelles; three frontal, one buccal, one postoral ventral, usually one frontoventral cirrus; two long ventral cirral rows, average of 40 and 38 cirri on left and right row, respectively; 39 left and 41 right marginal cirri; three dorsal kineties; three caudal cirri; ~16 macronuclear nodules, invariably two micronuclei.

Type locality and ecology: Wuhan Botanical Garden, Wuhan (30°32′57′′N, 114°25′51′′E), China. Water temperature 21 °C GoogleMaps .

Type specimens: A protargol slide containing the holotype specimen (see Fig. 5B–D; registration no. LXT2016040803/1) and three paratype slides (registration no. LXT2016040803/2–4) were deposited in the Laboratory of Protozoology , Ocean University of China .

Etymology: The species-group name wuhanense refers to the location (Wuhan) where the species was discovered.

Morphology: Body 135–200 μm × 40–60 μm in vivo, more or less fusiform in shape, with anterior end rounded. Tail conspicuous, highly contractile, about one-fifth to one-quarter of body length when fully extended in Petri dishes ( Fig. 5K), indistinct when contracted ( Fig. 5L, M). Ratio of length to width ~3–4:1, dorsoventrally flattened ~3:2 ( Fig. 5A, K–M). Macronucleus slightly left of cell median, composed of 15–19, averaging 16, small-sized (the biggest 7 μm × 9 μm on average; the smallest 5 μm × 6 μm on average) globular to ellipsoidal nodules. Invariably two globular to ellipsoidal micronuclei, near macronuclear nodules, ~4–6 μm across, only slightly smaller than macronuclear nodules ( Fig. 5C, D, G, H). One contractile vacuole ~12 μm across in diastole, near left margin of body about at level of cytostome ( Fig. 5A, G, L). Cortex flexible. Cortical granules, colourless, spherical, ~ 1–1.5 μm across, irregularly distributed throughout the cortex dorsally ( Fig. 5F, J). Cytoplasm colourless, middle region of cell usually packed with numerous shining granules (~1–3 μm diameter) and food vacuoles containing various algae ( Fig. 5E, I, N), rendering cells opaque and with a dark appearance at low magnification ( Fig. 5K–M). Cells crawl slowly on substrate and among debris.

Cilia of cirri ~8–10 μm long in vivo, except for three moderately enlarged frontal cirri, ~12–15 μm in length. Invariably one buccal and one postoral ventral cirrus. Usually one frontoventral cirrus (one out of 14 specimens analysed having no frontoventral cirrus). Two long, slightly obliquely arranged ventral cirral rows, both extending subterminally. Left ventral cirral row beginning about at level of rightmost frontal cirrus, comprising 30–49 cirri; right ventral cirral row with 34–48 cirri, starting near level of posterior third of buccal cavity. Left and right marginal cirral rows both reaching to posterior end of cell, composed of 31–48 and 34–45 cirri, respectively ( Fig. 5B, D). Three bipolar dorsal kineties with dorsal bristles ~3 μm long in vivo and closely spaced ( Fig. 5C, F, I). Three caudal cirri (10–12 μm long in vivo) positioned at the tip of tail, inconspicuous and not distinguishable from marginal cirri ( Fig. 5A, C).

Adoral zone occupied ~25% of body length in protargol-stained specimens. Buccal cavity narrow, with right margin of cavity near cell midline. Adoral zone slightly bipartite, with inconspicuous gap between distal and proximal parts comprising five to nine and 15–23 membranelles, respectively ( Fig. 5D, H, I). Bases of membranelles in distal part comprising three short, equal-length rows of kinetosomes, and those in proximal part containing four rows, one short and three long ( Fig. 5B, D). Undulating membranes more or less in Oxytricha pattern, almost equal in length, slightly curved and optically intersecting in middle part; paroral multiple rowed, commences slightly ahead of single-rowed endoral ( Fig. 5B, D, H).

18S RRNA GENE SEQUENCE AND PHYLOGENETIC ANALYSES

( FIG. 6)

The partial sequence of the 18S rRNA gene of Strongylidium guangdongense sp. nov. (GenBank accession number: MF113406 View Materials ) is 1670 bp long and has a G + C content of 45.15%. In Strongylidium wuhanense sp. nov. (GenBank accession number: MF113407 View Materials ) the gene is 1696 bp long and has a G + C content of 45.11%.

The nodes from the topologies generated with ML and BI were generally concordant ( Fig. 6). As described in previous studies ( Chen et al., 2016, 2017; Dong et al., 2016; Huang et al., 2016; Kumar et al., 2016; Li et al., 2016, 2017; Luo et al., 2016, 2017; Park et al., 2017), 18S rRNA gene sequences from Stichotrichida and Sporadotrichida intermingle, and neither order is monophyletic. The family Spirofilidae sensu Lynn (2008) is not monophyletic, as the type genus Hypotrichidium nests in the large group of oxytrichids. Stichotricha aculeata branched as sister to ‘core urostylids’, and Strongylidium species fell within the Strongylidium – Hemiamphisiella – Pseudouroleptus group, which is fully supported (ML/BI, 100/1.00). The genus Strongylidium formed a fully supported monophyletic group (ML/BI, 100/1.00) with the new species, Strongylidium guangdongense sp. nov. and S. wuhanense sp. nov., nested inside.