Strongylidium koreanum n. sp. (Protozoa: Ciliophora), a new soil species from South Korea Author Chae, Kyu-Seok Department of Biological Sciences and Bioengineering, Inha University, Incheon 22212, South Korea. Author Park, Kyung-Min 0000-0002-6125-4405 Department of Biological Resources Research, National Institute of Biological Resources, Incheon 22689, South Korea. kmpark 315 @ korea. kr; https: // orcid. org / 0000 - 0002 - 6125 - 4405 kmpark315@korea.kr Author Min, Gi-Sik Department of Biological Sciences and Bioengineering, Inha University, Incheon 22212, South Korea. text Zootaxa 2023 2023-01-05 5227 2 194 204 journal article 276837 10.11646/zootaxa.5227.2.2 aae39de8-dddf-4a3f-afcc-3bb248e44cb0 1175-5326 7518498 51A480AD-6FD5-4FDC-9EC9-24441DB568AD Comparison of S. koreanum n. sp. with morphologically related species In the comprehensive revision of Strongylidium by Paiva & Silva-Neto (2007) , Strongylidium spp. were divided into five groups. Group I is characterized by two long ventral and two marginal cirral rows, which includes the type species S. crassum Sterki, 1878 . To date, 17 species have been assigned to group I, and S. koreanum n. sp. was found to belong to this group. S. koreanum n. sp. should be compared with S. orientale , S. pseudocrassum , S. contortus , and S. crassum , considering its two macronuclear nodules and position of the contractile vacuole ( Table 2 ). Strongylidium orientale is highly similar to S. koreanum n. sp. in the number of adoral membranelles and the left ventral, left, and right marginal cirri. By contrast, both differ from anterior end of the right ventral cirri (above the proximal end of the adoral zone of membranelles vs. below), cortical granules (present vs. absent) and habitat (brackish water vs. terrestrial) ( Chen et al . 2013 ). TABLE 2. Comparison of morphological features in Strongylidium koreanum n. sp. with those of closely related congener.

Characteristic a	Strongylidium koreanum n. sp.	S. orientale	S. pseudocrassum	S. crassum	S. contortus
Body length (live)	125–150	80–120	80–120	120–180	140–170
Body length (stained)	85–120 (105.2c)	107–138 (123.7c)	59–105 (79.6c)	NA	NA
Body width (stained)	21–46 (31.7c)	42–71 (55.6c)	13–40 (28c)	NA	NA
Cortical granules	Absent	Present	Present	NA	NA
Anterior end of right ventral cirral row	Posterior of proximal end of adoral zone of membranelles	Near posterior end of undu- lating membranes	Near posterior end of undu- lating membranes b	Near posterior end of undu- lating membranes b	Near middle of undulating membranes b
AM, No.	23–32 (26.8c)	23–28 (26.2c)	19–29 (24.6c)	NA	NA
LVC, No.	27–42 (35c)	33–45 (37.5c)	22–36 (30.3c)	ca. 21b	ca. 43b
RVC, No.	15–28 (21.4c)	23–42 (31c)	12–32 (24.7c)	ca. 24b	ca. 46b
PVC, No.	1	0–2	1	0b	1b
LMC, No.	23–36 (29.3c)	26–36 (30.8c)	17–33 (22.7c)	ca. 15b	NA
RMC, No.	30–46 (37.7c)	28–42 (35.1c)	18–35 (28.4c)	ca. 28b	NA
Ma, No.	2	2	2–4	2b	2b
Mi, No.	2–3	1–3	2–5	1 (between Ma)	2b
CC, No.	3–4	3	3	3b	3b
Habitat	Terrestrial	Brackish water	Freshwater	Terrestrial	Freshwater
Data source	This study	Chen et al . (2013)	Paiva & Silva-Neto (2007)	Kahl (1932)	Gelei (1954)

a AM, adoral membranelles; CC, caudal cirri; LMC, left marginal cirri; LVC, left ventral cirri; Ma, macronuclear nodules; Mi, micronuclei; No., number; PVC, postoral ventral cirri; RMC, right marginal cirri; RVC, right ventral cirri. b Data from the illustrations. c Mean value. NA, not available (or not clearly recognizable). FIGURE 4. Dividers of Strongylidium koreanum n. sp. after protargol impregnation. A–D. Ventral and dorsal views of middle dividers showing the migrating cirri. E–H. Ventral and dorsal views of late dividers. CC, caudal cirri; DK1-3, dorsal kineties 1–3; DKA, anlagen of dorsal kineties; I–VI, anlagen of frontoventral cirri I–VI; LMA, left marginal anlage; Ma, macronuclear nodules; Mi, micronuclei; RMA, right marginal anlage. Scale bars 100 μm. Strongylidium pseudocrassum can be distinguished from S. koreanum n. sp. by its macronuclear nodules (2–4 vs. 2), distance from the anterior edge of the cell to the anterior end of the right ventral cirral row (9–26 µm vs. 37–45 µm), anterior end of the right ventral cirri (above the proximal end of the adoral zone of membranelles vs. below), cortical granules (present vs. absent) and habitat (freshwater vs. terrestrial) ( Paiva & Silva-Neto 2007 ). The data for S. contortus were insufficient because of the absence of a staining method. Thus, the characteristics seen in the illustrations were used. Strongylidium contortus differs from S. koreanum n. sp. in the number of right (ca. 46 based on the figure vs. 15–28, mean 21) ventral cirri, anterior end of right ventral cirri (above proximal end of adoral zone of membranelles vs. below), and habitat (freshwater vs. terrestrial) ( Gelei 1954 ). FIGURE 5. Phylogenetic tree inferred from the 18S rRNA gene sequences showing the position of Strongylidium koreanum n. sp. based on the maximum likelihood (ML) and Bayesian inference (BI) methods. TIM2 + I (0.6080) + G (0.4720) was selected as the best model from jModelTest version 2.1.7. Support values at the nodes represent the bootstrap values of maximum likelihood analysis and the posterior probability of the BI model. Dashes denote bootstrap values <50% or different topologies in ML and BI phylogenies. Strongylidium crassum can be separated from S. koreanum n. sp. by the absence of a postoral ventral cirrus (vs. present), anterior end of right ventral cirri (above proximal end of adoral zone of membranelles vs. below), and single micronuclei located between two macronuclear nodules (vs. 2) ( Kahl 1932 ).