Psilochasmus oxyurus

Psilochasmus oxyurus (Creplin, 1825) Fig. 3 Description. Based on six adult specimens (measurements of illustrated specimen are given in text; measurements of entire series are given in Table 2). Body elongate, cylindrical, somewhat wider near level of testes, 4,189 × 615, with narrow muscular, retractile tail-like process. Body length to width ratio 6.8. Ratio of body width at level of testes to body width at level of ventral sucker 1.0. Tegument armed. Forebody length represents 26 % of body length. Oral sucker subterminal, elongate-oval, 294 × 282, sometimes withdrawn under surface of tegument. Ventral sucker protuberant with deep cavity, consisting of strongly muscular portion and extensive surrounding sub-tegumental rim, larger than oral sucker, 609 × 586. Oral sucker to ventral sucker width ratio 0.5. Prepharynx short, not observed in holotype. Pharynx muscular, elongate-oval, smaller than oral sucker, 145 × 127. Oral sucker to pharynx length ratio 2.0; oral sucker to pharynx width ratio 2.2. Esophagus muscular, bifurcating anterior to level of ventral sucker, 328. Ceca thin-walled, extending to near posterior end of body. * Only observed in holotype. Testes tandem, in posterior half of body, weakly or strongly lobate. Anterior testis 485 × 258; posterior testis 517 × 236. Cirrus-sac elongate, slender, reaching level of ovary or anterior to it, 1,197 × 100. Internal seminal vesicle unipartite, tubular, with broader proximal part. Pars prostatica indistinct. Genital pore immediately anterior to level of ventral sucker. Ovary oval, median or submedian, pretesticular, 180 × 148. Mehlis’ gland between level of ovary and anterior testis. Uterine seminal receptacle present. Laurer’s canal not observed. Vitellarium distributed throughout most of hind body length, absent in tail; most follicles lateral to gonads, uterus and cirrus-sac. Vitelline reservoir between level of ovary and anterior testis. Eggs not numerous, ≤ 17 present, 79–99 × 49–60. Excretory pore subterminal. Excretory bladder not readily observed. Taxonomic summary. Type host: Aythya marila (L.) (Anseriformes: Anatidae). Host in this study: Anas crecca L. (Anseriformes: Anatidae). Site of infection: small intestine. Locality in this study: Skadovsk District, Kherson Region, Ukraine (46°07'55.6"N, 32°13'40.7"E). Specimens deposited: Vouchers: HWML -218106, labeled Anas crecca, small intestine, Skadovsk District, Kherson Region, Ukraine, 31 Aug 2011, coll. V. V. Tkach. Representative DNA sequences: PX 118872 (ITS region + 28 S); PX 114583 (nad 1). Remarks. The original description of the species by Creplin (1825) and redescription by Braun (1902) lack most details and measurements provided in descriptions of other echinostomatoid taxa. Despite this, the morphology (quantitative and qualitative characters) of our specimens of P. oxyurus closely conforms to the original description by Creplin (1825) and redescription by Braun (1902) (Table 2). Importantly, we provide molecular data associated with our described specimens of P. oxyurus.