Hemionchos arthanai, Suryaningtyas & Neitemeier-Duventester & Damriyasa & Haseli & Palm, 2025

Suryaningtyas, Endang Wulandari, Neitemeier-Duventester, Xaver, Damriyasa, Made, Haseli, Mohammad & Palm, Harry W., 2025, Trypanorhynch cestodes of Mobula thurstoni (Lloyd) from Bali, Indonesia, including the description of Hemionchos arthanai sp. nov. (Cestoda: Eutetrarhynchidae Guiart, 1927), Zootaxa 5729 (2), pp. 370-382 : 372-374

Hemionchos arthanai sp. nov.

( Figs 1 , 2A–C , 3A–E )

Type host: Mobula thurstoni (Lloyd) .

Type locality: Lombok Strait , Indonesia .

Site in host: Stomach.

Type material: Holotype ( MZB, MZBCa 222); 5 paratypes ( MZB, MZBCa 223 & 224, 2 slides; ZMB, E.7773- 5, 3 slides).

Etymology:The specific epithet is in honor to Prof.Wayan Arthana, former Dean of the Faculty of Marine Science and Fisheries, Udayana University, Bali, who supported our fish parasitological research in Bali, Indonesia.

Description

[Based on whole mounts of 8 immature specimens; 2 specimens observed with SEM.] Worms small, slender, elongated; immature specimens 1.057 –1.841 mm (1.501, N = 8) long, maximum width 187 at level of bothria, with 1–6 (4; N = 12) immature segments. Scolex acraspedote ( Fig. 1A ), 962–1,167 (1,051, N = 8) long. Scolex width 127–187 (163, N = 8) at level of pars bothrialis, 80–111 (93, N = 8) at level of pars vaginalis, 101–141 (117, N = 8) at level of pars bulbosa.

Surface of scolex smooth without transverse annulations (scutes). Two oval bothria, convex in middle; margin of bothrium entire, with 2 prominent internal ridges running from posterior margin near midline to tentacle orifices ( Fig. 3A ); bothria 100–162 (133, N = 8) long, 47–80 (65, N = 8) wide. Pars vaginalis longer than pars bothrialis. Pars bothrialis 135–179 (154, N = 6) long, pars vaginalis 662–850 (753, N = 6) long, pars bulbosa 260–335 (305, N = 8) long. Scolex ratio (pars bothrialis: pars vaginalis: pars bulbosa) 1.0: 4.7–4.9: 1.8 – 2.0 (1.0: 4.8: 1.9; N = 6).

Prebulbar organs present, gland cells inside bulbs absent; bulbs 201–316 (270, N = 8) long, 19–33 (26, N = 8) wide; bulb width: length ratio 1.0: 9.6–10.6 (10.4; N = 6); retractor muscles originate at base of bulbs. Pars postbulbosa very short or absent. Tentacle sheaths slightly sinuous to straight, 12–19 (16, N = 8) in diameter. Tentacle elongate when everted, 677–767 (705, N = 5) long, without prominent basal swelling; tentacle width 16–21 (19, N = 7) at level of basal region, 17–21 (18, N = 5) at level of metabasal region, and 16 (N = 1) at level of apical region. Tentacles with 44 (N =1) rows of hooks.

Tentacular armature heteroacanthous typical, heteromorphous. Principal rows of metabasal tentacular armature begin on bothrial surface, terminate on antibothrial surface; 5 hooks per row, elongated cavities inside hook tips present. Hooks solid, with cavity in tips of hooks 1–4 (1´–4’). Hooks 5 (5’) solid, without cavity inside tip.

Additional small hooks (alpha) present between hook files 1 and 1’ on bothrial surface next to 1’, uncinate; 4–5 (5, n = 4) long, base 2–3 (3, n = 4) long. Hook files 1(1’) separated by distinct space on bothrial surface, falciform, without prominent anterior extension of base, with cavity and notch at tip, 12–13 (13, n = 4) long, base 5–6 (5, n = 4) long; hooks 2(2’) uncinate to falciform with cavity and notch at tip, 14–15 (15, n = 4) long, base 4–5 (4, n = 4) long; hooks 3(3’) elongated falciform, with cavity and notch at tip, 15–18 (17, n = 4) long, base 4–5 (4, n = 4) long; hooks 4(4’) elongate, with a spiniform blade and elongated base, smaller than 3(3’), with cavity and notch at tip, 14 (n = 4) long, base 4–5 (4, n = 4) long; hooks 5(5’) small, falciform, without cavity and notch at tip, 7–9 (8, n = 4) long, base 2–4 (3, n = 4) long.

Characteristic basal armature present, with 2 rows of enlarged uncinate hooks with robust blade on internal surface, 7–9 (8, n = 4) long, base 3–5 (4, n = 4) long, and smaller uncinate hooks on external surface, 6–8 (7, n = 4) long, base 3– 5 (4, n = 4) long, followed by 3 rows of slender uncinate to spiniform hooks with thin blade, 7–9 (8, n = 6) long, base 3 (n = 6) long, followed by characteristic 3 rows of conical, in part dorso-ventrally flattened, falcate hooks with a strongly recurved mucronate tip, 10–12 (11, n = 8) long, base 4–6 (5, n = 8) long.

Strobila acraspedote, anteriormost segments wider than long, 56–62 (58, n = 5) long, with maximum width 101–112 (109, n = 5), terminal segment longer than wide, 261–428 (364, n = 3) long, with maximum width 55–62 (59, n = 3). Cirrus pouch in mid segment region. Ovary posterior, testes anterior to cirrus pouch approx. 18 (N = 1) in number, 7–9 (8; N = 8) in diameter.

Remarks

Hemionchos arthanai sp. nov. is assigned to the genus Hemionchos due to cavities at hook tips, separation of hooks 1 and 1' on the bothrial tentacle surface, and presence of a small hook (alpha) associated with metabasal hooks 1' ( Campbell & Beveridge 2006; Beveridge & Bennett 2022).

The new species differs from H. striatus by its distinctive basal armature, which has rows of enlarged, erect, dorso-ventrally flattened hooks, each with a tip featuring a small mucronate extension and lacuna—features absent in H. striatus . It is distinguished from H. maior Campbell and Beveridge, 2006 and H. australis Campbell and Beveridge, 2006 by having fewer, rather than numerous, enlarged erect flattened hooks in its basal armature. Unlike H. mobulae , which has ring structures (scutes) on the scolex and uncinate metabasal hooks 1(1’), the new species lacks ring structures (scutes) and possesses falciform metabasal hooks 1(1’).

The new species differs from the three undetermined Hemionchos species A , B, and C of Beveridge & Bennett (2022) by having, rather than lacking, a distinctive basal armature and by the presence of accessory hooks adjacent to metabasal hooks 1’, a feature absent in Hemionchos A, B, and C.

Although the metabasal armature of H. arthanai sp. nov. is morphologically consistent with those congeners possessing the additional small hooks (alpha) between the hook files 1 and 1’, the tip cavity of its hooks also serves as a distinguishing feature at the interspecific level. The metabasal hooks 4(4’) of the new species have a cavity at the tips, while the tips of the same hooks of H. australis Campbell and Beveridge, 2006 , H. mobulae , and H. striatus are solid. The metabasal armature of H. maior is unknown.

Another characteristic feature of H. arthanai sp. nov. is the absence of transverse annulations (scutes) covering the scolex, in contrast to H. striatus , H. mobulae , H. maior (see Campbell & Beveridge 2006), Hemionchos sp. A , and Hemionchos sp. C (see Beveridge & Bennett 2022). A smooth scolex has only been described in H. australis and Hemionchos sp. B ( Beveridge & Bennett 2022).

Figures

FIGURE 1. Hemionchos arthanai sp. nov. from the stomach and spiral valve of Mobula thurstoni. (A) Scolex with immature strobila. (B) Bothrial tentacle surface, metabasal. (C) Profiles of hooks of principal rows. (D) Bothrial tentacle surface, basal (E) Antibothrial tentacle surface, basal. (F) Muscular bulb with its prebulbar organ. Scale bars: (A) 100 µm; (B, C, D, E) 20µm; (F) 50 µm.

FIGURE 2. Confocal laser scanning microscope (CLSM) images of Hemionchos spp. from the stomach and spiral valve of Mobula thurstoni. A-C: H. arthanai sp. nov. (A) Scolex with four tentacles. (B) Overview of four tentacles. (C) Basal armature. D, E: H. mobulae (D) Whole specimen with four tentacles. (E) Tentacle with cavity in hook tips (arrows). F-I: H. striatus (F) Scolex with four tentacles (G) Overview of tentacles with cavity in hook tips (white tips). (H) Basal and metabasal tentacular armature, internal to bothrial surface. (I) Basal and metabasal tentacular armature, bothrial surface. Scale bars: (A) 150 µm; (B) 30µm; (C) 20µm; (D) 200 µm; (E) 30µm (F) 100 µm; (G) 30 µm. (H) 20 µm. (I) 20 µm.

FIGURE 3. Surface ultrastructure of the scolex and tentacular armature of Hemionchos spp. A-E: Hemionchos arthanai sp. nov. (A) Scolex and tentacular armature. (B) Two tentacles. (C) Metabasal armature, bothrial surface. (D) Basal armature, bothrial and antibothrial surfaces. (E) Basal armature, antibothrial surface. F-L: Hemionchos mobulae (F) Scolex with transverse annulations. (G) Tentacles. (H) Basal armature with cavity in hook tip (arrow). (I) Scolex surface with transverse annulations. (J) Transverse annulations consisting of undulated filitriches of different length. (K) Bothrial surface. (L) Aristate gladiate spinitriches on bothria. M-P: H. striatus (M) Scolex with four tentacles. (N) Metabasal armature, bothrial surface. (O) Basal armature, internal surface. (P) Basal armature, bothrial and antibothrial surfaces. Scale bars: (A) 100 µm; (B,) 20 µm; (C, D) 10 µm; (E) 2 µm; (F) 100 µm; (G) 20 µm; (H) 2 µm; (I, J) 2 µm; (K) 10 µm; (L) 1 µm; (M) 100 µm; (N) 10 µm; (O) 2µm (P) 10 µm.