Helicometra antarcticae Holloway & Bier, 1968

Sokolov, Sergey G., Shchenkov, Sergei V., Khasanov, Fuat K., Kornyychuk, Yuliya M. & Gordeev, Ilya I., 2022, Redescription and phylogenetic assessment of Helicometra antarcticae Holloway & Bier, 1968 (Trematoda, Opecoelidae), with evidence of non-monophyletic status of the genus Helicometra Odhner, 1902, Zoosystema 44 (15), pp. 423-433 : 426-427

Helicometra antarcticae Holloway & Bier, 1968

( Fig. 1 )

Helicometra antarcticae Holloway & Bier, 1968: 31 . — Bray 1979: 402.

Neohelicometra antarcticae – Sekerak & Arai 1974: 730.

TYPE LOCALITY. — Ross Sea.

TYPE MATERIAL. — Holotype • Ross Sea, McMurdo Sound; intestine of the Antactic toothfish Dissostichus mawsoni ; 11.XI.1964; USNPC1358823 .

Paratype • Ross Sea, McMurdo Sound; intestine of zoarcid eelpout Rhigophila dearborni ; 25.XI.1964; USNPC 1358824 .

MATERIAL EXAMINED. — Ross Sea • 6 whole-mounted adult specimens, 2 slides with isolated ovarian complex, 5 slides with isolated terminal genitalia; intestine of Dissostichus mawsoni ; 75°44’7”S, 172°56’8”W; 12.I.2012; IPEE RAS 14315 (for whole-mounted specimens) • 3 whole-mounted adult specimens; intestine of Dissostichus mawsoni ; 75°40’3”S, 172°26’1”W; 21.I.2013; IPEE RAS 14316 • 1 whole-mounted adult specimen; intestine of Dissostichus mawsoni ; 75°28’2”S, 174°37’6”W; 26.I.2013; IPEE RAS 14317 • 1 sequenced adult specimen; intestine of Dissostichus mawsoni ; 75°25’3”S, 174°32’7”W; 12.I.2012; GenBank: OK644193 (28S rRNA gene) .

DESCRIPTION

General morphology and digestive system

Body elongate-oval, length 2.969 -5.895 (3.844), maximum width 799-1.527 (1.174) at mid-body. Tegument unarmed. Pre-oral lobe absent. Oral sucker cup-shaped, 357-499 (419) / 271-585 (419), mouth opening terminal. Ventral sucker globular or subglobular, 357-628 (475) / 399-585 (497). Oral sucker to ventral sucker width ratio 1:1.00-1.53 (1:1.22). Forebody 24.5-30.9 (27.7)% of body length. Prepharynx short, distinct. Pharynx well-developed, 113-191 (149) / 106-184 (141). Oesophagus 92-289 (171). Pharyngeal and oesophagus glands distinct. Intestinal bifurcation in middle or posterior third of forebody. Caeca blind; distance from caecal ends to posterior end of body reaching 395-1031 (641).

Male reproductive system

Two testes, variously lobed, separate to slightly overlapped, oblique, post-equatorial; anterior testis sinistro-submedian, 257-514 (390) / 285-499 (384), posterior testis median or dextro-submedian, 299-528 (408) / 314-585 (445). Posttesticular region 23.3-33.3 (27.4)% of body length. Cirrus-sac well developed, 311-735 (589) / 155-261 (201), overlaps usually 20.5-78.8 (44.6)% of ventral sucker, occasionally extends to 142 beyond posterior margin of ventral sucker. Internal seminal vesicle long, tubular, folded. Pars prostatica tubular, surrounded by numerous prostatic gland-cells. Ejaculatory duct and cirrus distinct, surrounded by spongy tissue. Genital atrium distinct. Genital pore usually median, occasionally slightly dextro-submedian, just posterior to intestinal bifurcation, 169-424 (225) from anterior margin of ventral sucker.

Female reproductive system

Ovary variously lobed, median or dextro-submedian, anterodextral to anterior testis, separate or slightly overlapping, 200-414 (258) / 285-599 (409). Oviduct anterior to ovary, forming oötype after connecting with canalicular seminal receptacle and common vitelline reservoir duct. Ovicapt distinct. Canalicular seminal receptacle saccular, antero-dextral to ovary. Laurer’s canal opening sinistro-submedially approximately at level of anterior margin of seminal receptacle. Mehlis’ gland extensive, diffuse. Uterus pre-ovarian, coiled, intercaecal. Metraterm muscular, opening into genital atrium antero-dorsally.Eggs operculate, with long, unipolar filament; length without filament 66.8-85.0 (77.9), width 30.4-42.5 (35.7). Vitellarium follicular; follicles in two lateral fields, extending from intestinal bifurcation level or from genital pore level or, occasionally, from midlevel distance between genital pore and anterior margin of ventral sucker to near posterior end of body; fields overlapping caeca along entire length dorsally and at level of posterior testis and in posttesticular region ventrally, encroaching over ventral surface of caeca at level of proximal uterine coils, ovary and anterior testis, extracaecal on ventral side of body anteriorly to ovary, usually not confluent, occasionally almost confluent in posttesticular region but distinctly separated over excretory vesicle; anterior border of ventral follicles some distance posterior to that of dorsal follicles.

Excretory system

Excretory pore terminal. Excretory vesicle I-shaped, extending approximately to posterior margin of ventral sucker; posterior end surrounded by numerous glands and small subterminal muscular sphincter.

Figures

FIG. 1. — Helicometra antarcticae Holloway & Bier,1968 from intestine of the Antarctic toothfish,Dissostichus mawsoni Norman,1937, Ross Sea:A, whole mount, ventral view; B, terminal genitalia, lateral view; C, ovarian complex, ventral view. Abbreviations: С, cirrus everted through genital atrium; ej, ejaculatory duct; ga, genital atrium; isv, internal seminal vesicle; lc, Laurer’s canal; mg, Mehlis’ gland cells; mt, metraterm; oc, ovicapt; oo, oÖtype; ov, ovary; pc, prostatic cells; pp, pars prostatica; sr, seminal receptacle; vr, common vitelline reservoir. Scale bars: A, 1 mm; B, 0.2 mm; C, 0.08 mm.