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

STRONGYLIDIUM GUANGDONGENSE SP. NOV.

( FIGS 2–4; TABLE 1)

urn:lsid:zoobank.org:act:157A624A-F01B-4D29-9823-D0D4F30D8329

Diagnosis: Body ~100–150 μm × 40–50 μm in vivo; cell outline more or less fusiform, with rounded anterior end and inconspicuous tail; cortical granules colourless, spherical, ~1–1.5 μm across; ~30 adoral membranelles; three frontal, one buccal, one postoral ventral, usually one frontoventral cirrus; two long ventral cirral rows, averaging 34 and 32 in left and right rows, respectively; 29 left and 35 right marginal cirri; three dorsal kineties; three caudal cirri; about eight macronuclear nodules; brackish water habitat.

Type locality and ecology: Mangrove National Nature Reserve Park , Shenzhen (22°31′53′′N, 114°00′34′′E), China GoogleMaps .

Type specimens: A protargol slide containing the holotype specimen (see Figs 2B, C, 3A, B; registration no. LXT2015120101/1) and five paratype slides (registration no. LXT2015120101/2–6) were deposited in the Laboratory of Protozoology , Ocean University of China .

Etymology: The species-group name guangdongense refers to the area (Guangdong) from which the species was collected.

Morphology: Body 100–150 µm × 40–50 µm in vivo, somewhat fusiform in shape, with rounded anterior end and tapered posterior end, with inconspicuous tail, flexible, only slightly contractile ( Fig. 2A, G–I). Ratio of length to width ~5:2–3:1, dorsoventrally flattened ~3:2. Macronucleus left of cell median, composed of four to 12, averaging eight, globular to ellipsoidal nodules. One to seven globular micronuclei near, or adjacent to, macronuclear nodules, ~2–8 µm across, usually one or two larger-sized (3–8 µm, on average 4 µm) micronuclei in starved cells, four to seven smaller-sized (2–3 µm) micronuclei in raw cultured cells after protargol staining ( Figs 2C, 3C, H–K). One contractile vacuole ~12 µm in diameter in diastole, about at level of cytostome near left margin of body ( Fig. 2A, I). Cortical granules colourless, spherical, ~1–1.5 µm across, arranged in longitudinal rows along cirral rows and dorsal

Abbreviations: AZM1, distal part of adoral zone of membranelles; AZM2, proximal part of adoral zone of membranelles; CV, coefficient of variation expressed as a percentage; mean, arithmetic mean; N, number of specimens examined.

*Data for Strongylidium guangdongense sp. nov.

†Data for Strongylidium wuhanense sp. nov.

‡Data for the largest macronuclear nodule.

§Data for the smallest macronuclear nodule.

kineties, irregularly distributed between cirral rows and dorsal kineties, easily stained with protargol, and some granules extruded, forming hair-like structures on the cell surface in protargol-stained specimens ( Figs 2D–F, 3L, M). Cytoplasm colourless, packed with food vacuoles containing numerous diatoms, usually present in middle region of cell, rendering cells slightly brownish in appearance at low magnification ( Fig. 2E, G–J). Cells crawl slowly on substrate and among debris in the bottom of Petri dishes.

Usually three, rarely four moderately enlarged frontal cirri ( Fig. 3C–G), rightmost just behind distal end of adoral zone, with cilia ~12–15 μm long in vivo. All other cirri ~8–10 μm long, except for the caudal cirri (10–12 μm; Fig. 2A, D). Invariably one buccal, one postoral ventral cirrus and usually one, sometimes two frontoventral cirri, rarely absent (three out of 23 specimens analysed having two frontoventral cirri, only one cell with no frontoventral cirri; Figs 2B, 3C–E). Two long, slightly oblique, sigmoid ventral cirral rows. Left ventral cirral row commences approximately near rightmost frontal cirrus, comprising 29–39 cirri, terminated at ~80% of cell length. Anterior, middle and posterior parts of left ventral cirral row generated from anterior segments of frontal-ventral-transverse cirral anlage (FTVA) VI and IV and whole of V, with cirri of the three parts usually arranged in a typical row ( Fig. 3A, C–E); occasionally, cirri from anlage VI located slightly left of the row ( Fig. 3F, G). Right ventral cirral row starts near level of posterior third of buccal cavity, ends slightly subterminally, comprising 24–38 cirri. Left and right marginal cirral rows both reach posterior end of cell, composed of 21–36 and 25–48 cirri, respectively; several anteriormost right marginal cirri reach dorsal surface ( Figs 2B, C, 3A, B). Three dorsal kineties extend almost entire length of cell, one caudal cirrus at end of each dorsal kinety ( Figs 2A–C, 3B), dorsal bristles ~3 μm long in vivo.

The adoral zone occupied ~27% of body length after protargol staining. Adoral zone is composed of 25–34 membranelles, with cilia ~15–18 μm long in vivo. Bases of membranelles are unequal in length, those in distal part comprising three short, equal-length rows of kinetosomes, those in proximal part with four rows, one short and three long ( Figs 2B, 3C). Buccal cavity narrow, with right margin of cavity in midline ( Fig. 2A, D). Paroral and endoral membranes more or less in Oxytricha pattern, almost equal in length, slightly curved, optically intersect near anterior end of the latter ( Figs 2B, 3A, C–G). Endoral membrane comprising single row of kinetosomes, starting at level of buccal cirrus. Paroral with multiple rows of kinetosomes, begins slightly anterior to endoral ( Figs 2B, 3A, C–G).

Morphogenesis: Stomatogenesis commences with the formation of the oral primordium of the opisthe, a longitudinal field of closely spaced basal bodies behind the parental adoral zone of the membranelles, between the left ventral cirral row and the left marginal cirral row ( Fig. 4A). Parental cirri do not contribute to formation of the oral primordium.

In an early divider ( Figs 3N, 4B), basal bodies for the oral primordium proliferate and differentiate into new membranelles, beginning at the anterior portion and progressing posteriorly. At the same time, in the opisthe, the undulating membrane anlage appears to the right of the oral primordium. The parental postoral ventral cirrus disappears and may contribute to the formation of the FVTA but may also simply be resorbed. Another FTVA (probably FVTA V) originates from the left ventral cirral row. Simultaneously, in the proter, the parental buccal cirrus (II/1) begins to dedifferentiate into FVTA II.

In an early middle divider ( Figs 3O, 4D), all the FVTA have formed. In the proter, the undulating membrane anlage is formed from the old undulating membranes, and the FVTA III originates from the parental frontoventral cirrus. For both the proter and opisthe, the left and right ventral cirral rows dedifferentiate and intrakinetally form FTVA V and VI, respectively. However, some key stages were not observed, so the origins of the other FVTA are not clear.

In the middle stage ( Fig.4E), the undulating membrane anlagen splits longitudinally into paroral and endoral membranes, which give rise to the leftmost frontal cirrus in both proter and opisthe. All FVTA lengthen to long streaks and begin to differentiate into new cirri.

In the late stage ( Figs 3Q, 4G), the FVTA differentiate into new cirri, which migrate to their final position in both the proter and the opisthe: FVTA II gives rise to the middle frontal cirrus and the buccal cirrus; FVTA III contributes to the rightmost frontal and usually one frontoventral cirrus; FVTA IV differentiates into one postoral ventral cirrus and probably two cirri of the middle part of the left ventral cirral row; cirri originating from FVTA V form the posterior part of the left ventral cirral row; and FVTA VI contributes to the whole right ventral cirral row and the anterior part of left ventral cirral row.

The marginal cirral row anlagen develop intrakinetally through dedifferentiation of the parental cirri ( Fig. 4D, E). Then, all anlagen lengthen towards both ends of the dividing cell while the parental cirri are resorbed ( Fig. 4G). Dorsal kinety anlagen (DKA) originate de novo ( Figs 3P, 4C, F). In the late stage, one caudal cirrus is formed at the posterior end of each DKA ( Fig. 4H).

All macronuclear nodules fuse into a single mass and then divide ( Fig. 4A, C, D, F, H).