Microbothrium myzolepis, Ota, 2025

Microbothrium myzolepis n. sp.

( Figs 1 View Fig , 2 View Fig )

[New Japanese name: Futo-tsuno-zame-kagi-nashi-hada-mushi]

Holotype. MPM Coll.-No. 25318.

Paratypes. Four specimens ( MPM Coll.-No. 25319), 4 specimens ( KMNH IvR 600098–600101), and 4 specimens (KAUM-AT-3327–3329) .

Description. Body pyriform, 3051–3978 (3595; n = 12) long including haptor, 1939–2498 (2142; n = 13) wide at anterior margin of germarium. Haptor without sclerotized armature, diamond-shaped sucker to accommodate shape of host dermal denticle; lower half of haptor more muscular and thicker, deep inside, attaching to tip of dermal denticle of host; 546–696 (604; n = 12) long, 653–912 (739; n = 12) wide. Eyes absent.

Mouth opening subterminal of anterior body; two small protrusions on anterior side of mouth; pharynx bowlshaped with center protruding anteriorly, 248–369 (313; n = 13) long, 303–425 (381; n = 13) wide; esophagus absent; bifurcate intestinal cecum with numerous diverticula leading laterally and two medial diverticula dorsal to the anterior portion of the testis, not confluent posteriorly.

Testis subspherical, intercecal, midline at top of lower body, 432–729 (560; n = 13) long, 577–893 (668; n = 13) wide. Vas deferens exiting from anterior margin of testis, swelling to form seminal vesicle at left of seminal receptacle, extending anteriorly on dorsal side of vitelline reservoir, entering ejaculatory bulb ventrally. Ejaculatory bulb muscular, spherical to oval, not directly connected to penis but located ventral to base of the penis. Sclerotized tube extending from left side of ejaculatory bulb, turning once (n= 12) or twice (n = 1) to dorsal side, entering base of penis, and extending three-quarters of the penis length, 440–733 (582; n = 13) long. Penis weakly muscular, curved dorsoventrally, 294–507 (427; n = 13) long along curve; terminal quarter of duct not sclerotized.

Germarium spherical to oval, intercecal, situated slightly right at mid-body level, 195–364 (234; n = 13) long, 205– 455 (260; n = 13) wide. Oviduct arising from anterior part of germarium, receiving duct from posterior aspect of vitelline reservoir. Ovovitelline duct extending posteriorly, connecting duct from seminal receptacle, traveling anteriorly on dorsal side, and connecting with oötype base surrounded by Mehlis gland. Oötype traveling medially, opening ventrally at unarmed common genital pore located in upper third of body, at penis level. Vaginal pore unarmed, on ventral surface between left intestinal cecum and upper third of oötype, posterior to penis. Vaginal tube muscular, extending to seminal receptacle ventrally with slight bend. Seminal receptacle midbody, left of germarium. Egg ovate slightly angled, with long filament, 86–145 (110; n = 3) long, 64–94 (78; n = 3) wide without filament, in oötype.

Type host. Shortspine spurdog Squalus mitsukurii Jordan and Snyder, 1903 ( Squaliformes: Squalidae ).

Type locality. The East China Sea off Kuchino-erabu Island (30°25′N, 130°12′E), Yakushima Town   GoogleMaps , Kagoshima Prefecture, Japan.

Sites of infection. Body surface (dermal denticles).

Etymology. The new scientific name is from Ancient Greek words (myzō = suck + lepís = scale) and refers to the haptor of the new species holding the tip of host’s dermal denticle. The new Japanese name, “futo-tsuno-zame” refers to the host in Japanese, and “kagi-nashi-hada-mushi” means microbothriid.

Representative DNA sequences. INSDC accession numbers: LC805883 (28S rDNA, 1295 bp), LC805884 (18S rDNA, 1877 bp), LC805885 ( ITS1 - 5.8 S-ITS2, 909 bp), and LC805886 (cox1, 934 bp) . Each sequence obtained from two paratypes ( KMNH IvR 600100, 600101) were identical .

Remarks. Microbothrium myzolepis n. sp. exhibits the characteristic morphological features inherent to the genus, including singular testes, diverticulated intestinal ceca, rounded germarium, and unarmed penis accompanied by a sclerotized tube ( Nitta and Nagasawa 2017). This newly described species is distinct from M. lepidorhini by the vaginal pore situated posterior to the genital pore on the left side of the ventral body (vs. right: Guiart 1938; Brinkmann 1940, 1952a). It differs from M. tolloi by the unsclerotized vagina (vs. sclerotized: Brinkmann 1952b). The vagina of the new species displays a slight bend without sinusoidal or coiled attributes, but that of M. apiculatum was thick-walled and strongly muscular tube with tight sinuosity ( Saint-Remy 1891; MacCallum 1926a, b; Price 1938). In addition, the vaginal pole of M. myzolepis n. sp. opens at the posterior to the genital pore, while that of M. apiculatum opens at same level as genital pore ( Saint-Remy 1891; MacCallum 1926a, b; Price 1938). Microbothrium myzolepis n. sp. is separated from M. cirrhigalei n. sp. by the sclerotized tube associated with the penis completes one to two turns (vs. three) and the muscular vagina (vs. only the vaginal opening is muscular) ( Table 3 View Table 3 ).