Hysterocineta bellerophon, Obert & Zhang & Vďačný, 2023

Obert, Tomáš, Zhang, Tengyue & Vďačný, Peter, 2023, The search finds an end: the morphologically chimeric hysterocinetids belong to the subclass Hymenostomatia (Ciliophora: Oligohymenophorea), Zoological Journal of the Linnean Society 199 (1), pp. 97-123 : 103-108

publication ID	https://doi.org/ 10.1093/zoolinnean/zlad023
publication LSID	lsid:zoobank.org:pub:EC132BF4-4C98-49D5-99D8-01ED24128481
DOI	https://doi.org/10.5281/zenodo.8338020
persistent identifier	https://treatment.plazi.org/id/03B087E1-4B41-6404-FC6B-206F4FF0FAAF
treatment provided by	Plazi
scientific name	Hysterocineta bellerophon
status	sp. nov.

Treatment

Hysterocineta bellerophon sp.nov.

( Figs 3A View Figure 3 – 5 View Figure 5 , 4A–E View Figure 4 , 5A–E View Figure 5 , 6A–H View Figure 6 ; Table 1 View Table 1 )

ZooBank registration: urn:lsid:zoobank.org:act:2B80676C-F7CC-4F85-AF20-EC3330A119E0 .

Diagnosis: Body size about 170–270 × 75–150 µm in vivo. Body broadly to narrowly ovoid, with anterior end more narrowly rounded than posterior one. Anterior sucker forms an inverted, broadly U-shaped paưern, sucker arms about 15–46 µm long forming an angle of about 84°. Irregularly curved cylindroidal macronucleus extends through middle quarters of cell. A single contractile vacuole near posterior end of macronucleus. On average, 64 less and 105 right meridional ciliary rows; two subapical and two posterior sutures. Oral ciliature consists of a paroral membrane and three membranelles. Membranelle M1 runs only on peristome and terminates near entrance to infundibulum. Second membranelle cut in two segments at infundibular entry: distal segment confined to peristome and runs beside M1, while proximal segment M2 ʹ restricted to infundibulum and extends beside M3. Membranelle M3 starts at infundibular entrance and runs along M2 ʹ. Paroral membrane extends in parallel with M1 and M2 over peristome, while on opposite side as M2 ʹ and M 3 in infundibulum. Infundibular cilia describe 1.5 turns of a spiral.

Type locality: Waterlogged soil in the riparian zone of the Šúrsky kanál branch, Čierna voda river, Bratislava district, Slovakia, 48° 12ʹ 46.0″ N, 17° 13ʹ 25.3″ E GoogleMaps .

Type host: Octodrilus cf. gradinescui (Pop, 1938). ND1 and COI sequences of the type host have been deposited in GenBank under the following accession numbers: OP752213 and OP755299, respectively.

Type material: A DNA sample of the holotype specimen (CVsk 170 OG) has been deposited in the Natural History Museum, Vajanského nábrežie 2, 810 06 Bratislava, Slovakia (ID Collection Code 01427573). A paratype slide containing protargol-impregnated specimens (reg. no. 2023/5- ZTY) has been deposited at the Department of Zoology , Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia. Gene sequences: The 18S rRNA gene, ITS region-28S rRNA gene, 16S rRNA gene, and COI sequences of the holotype specimen have been deposited in GenBank under the following accession numbers: OP755209, OP755183, OP755234, and OP785732, respectively.

Etymology: Bellerophon (Βελλεροφῶν) was the greatest Corinthian hero of Greek mythology who baưled and killed the fantastical Chimera monster. The specific epithet reflects the fact that both nuclear and mitochondrial sequences obtained from this new species helped to overcome the misclassification of hysterocinetids in the subclass Scuticociliatia based on their chimeric morphology. The species-group name is treated as a noun in the nominative singular standing in apposition to the generic name (Article 11.9.1.2. of ICZN 1999).

Description: Body size about 170–270 × 75‒150 µm in vivo, while about 140–224 × 63–126 µm asser protargol impregnation ( Table 1 View Table 1 ). Body shape similar to P. simplex , i.e. broadly to narrowly ovoid with anterior end slightly more narrowly rounded than posterior one, anterior end rarely bluntly pointed ( Figs 3E View Figure 3 , 4B, D View Figure 4 ); length:width ratio 1.6–2.3:1, near 2:1 both in vivo and in protargol preparations; body laterally flaưened ( Figs 3A, C–L View Figure 3 , 4A, D View Figure 4 , 5E View Figure 5 ; Table 1 View Table 1 ).

Sucker occupies anterior body region, not delimited by shallow concavities on lateral body sides; forms an inverted, broadly U-shaped paưern. Angle formed by sucker arms about 84° on average; ventral arm slightly longer than dorsal one, i.e. on average 27.9 µm vs. 22.4 µm asser protargol impregnation ( Figs 3A, C–G, I–L View Figure 3 , 4A View Figure 4 , 5A, E View Figure 5 , 6A View Figure 6 ; Table 1 View Table 1 ). Sucker unciliated; no specific granules recognizable either in vivo or asser protargol impregnation ( Fig. 4B View Figure 4 ). Skeletal fibres emerge from anterior end of less ciliary rows, run almost in parallel with main body axis, i.e. do not follow curvature of sucker arms; comparatively short, namely 9–12 µm long asser protargol impregnation, and hence extending only in posterior sucker half; weakly impregnate with the protargol method used ( Figs 5A View Figure 5 , 6A View Figure 6 ).

Nuclear apparatus extends through middle quarters of cell, i.e. begins about 40 µm apart from anterior body end asser protargol impregnation. Macronucleus irregularly curved cylindroidal, approximately 64–140 × 14–35 µm in size asser protargol impregnation; nucleoli small, more or less globular, evenly distributed over macronucleus ( Figs 3A, C–L View Figure 3 , 4A, D View Figure 4 , 5E View Figure 5 , 6H View Figure 6 ; Table 1 View Table 1 ). Micronucleus not observed either in vivo or asser protargol impregnation (N = 10) and hence likely amicronucleate.

One contractile vacuole located near posterior end of macronucleus and slightly above beginning of cytopharynx, i.e. not situated within posterior vacuolar area; excretory pores not observed either in vivo or asser protargol impregnation ( Figs 3A, C–F, I–L View Figure 3 , 4A View Figure 4 ). Cortex flexible, not, or only slightly, furrowed by ciliary rows; no specific granules recognizable in vivo or in protargol preparations. Cytoplasm colourless; 3 µm-sized food vacuoles located in buccal area together with densely arranged granules (about 1 µm in diameter); vacuolar area extends anteriorly along ventral and dorsal body margin in a form of two pointed arms ( Figs 3A View Figure 3 , 4C, E View Figure 4 ). Swims moderately fast, rotating about main body axis; dies within half an hour asser extraction from host.

Somatic ciliature holotrichous, composed of monokinetids. Somatic cilia about 13 µm long in vivo, densely arranged in an average of 64 less and 105 right meridional rows ( Table 1 View Table 1 ). Less ciliary rows start below posterior sucker margin, while right ciliary rows begin at anterior sucker margin ( Figs 3G, H View Figure 3 , 4B View Figure 4 , 5A, B, E View Figure 5 , 6A View Figure 6 ). Individual rows densely spaced, i.e. approximately 1.6 µm from each other; irregularities on both body sides, though much more common on right posterior body half, namely, some rows shortened anteriorly and posteriorly, or with breaks causing switches between two adjacent or even between more distant rows ( Figs 3G, H View Figure 3 , 6G View Figure 6 , asterisk). Anterior end of some ventro- and dorsolateral ciliary rows abut to form an inconspicuous subapical secant system (suture) below each sucker arm ( Fig. 5A View Figure 5 , arrow). Likewise, posterior end of some ventro- and dorsolateral ciliary rows form a secant system close to each cell margin of right side; posterior sutures sometimes difficult to recognize due to irregular arrangement of basal bodies at posterior body region ( Fig. 3H View Figure 3 , arrows).

Oral apparatus located at posterior body pole and composed of an outer peristomial region and an inner infundibular part. Peristomial region follows curvature of posterior body margin, oriented perpendicularly to anteroposterior body axis, about 35 µm wide asser protargol impregnation ( Table 1 View Table 1 ). Outer oral cilia about 10 µm long in vivo. Infundibulum 15.4–48.1 µm long in protargol preparations; infundibular cilia about 6 µm long in vivo, form 1.5 turns of a spiral. Oral ciliature consists of a paroral membrane and three membranelles (M1–M3). First membranelle M1 made up of two rows of basal bodies, runs only on peristome, and terminates near entrance to infundibulum. Second membranelle cut in two segments at infundibular entry: (i) distal segment M2 built from two rows of basal bodies, confined to peristome, and runs beside M1; (ii) proximal segment M2 ʹ composed of three rows of basal bodies, restricted to infundibulum, and extends beside M3. Third membranelle M3 consists of two rows of basal bodies, starts at infundibular entrance, and extends along M2 ʹ. Paroral membrane made up of two rows of kinetosomes, extends in parallel with M1 and M2 over peristome, while on opposite side as M2 ʹ and M 3 in infundibulum; not segmented ( Figs 3B View Figure 3 , 4E View Figure 4 , 5C–E View Figure 5 , 6B–F View Figure 6 ; Table 1 View Table 1 ). Cytopharyngeal fibres not impregnated with the protargol method used.