Paranoplocephala primordialis Douthitt 1915

Paranoplocephala primordialis (Douthitt, 1915) (Fig. 2, Table 2) Syn. Andrya primordialis Douthitt, 1915. Redescription: Based on three specimens from T. hudsonicus (Tables 1 and 2). For the early uterus and other illustrations of the type material, see Douthitt (1915). Fully gravid strobila ca. 85 long (n=1) and 2.0 (n=1) wide (1.0 in Douthitt 1915). Number of proglottids ca. 300 (n=1). Proglottids craspedote, but velum very short or absent in well-relaxed specimens. Length/width ratio of mature proglottids 0.21–0.44 (0.33, n=6), of gravid proglottids 0.38–0.62 (0.46, n=5). Scolex simple, globular, rounded apically; width 0.46–0.53 (n=2) (0.475 in Douthitt 1915). Suckers 0.175–0.220 (0.20, n=8) in diameter, directed antero-laterally, embedded in scolex. Neck 0.5 (n=1) long, not clearly distinct from scolex, tapering posteriorly, minimum width (0.15–0.26, n=2) attained in region where segmentation first visible. Genital pores unilateral (n=1) or with multiple (18) alternations per strobila (n=1), opening slightly posterior to middle of proglottid margin in mature proglottids. Ventral longitudinal osmoregulatory canals of variable width (0.04–0.10, 0.058, n=7). Dorsal longitudinal osmoregulatory canals lateral to ventral longitudinal canals. Genital ducts passing dorsally to longitudinal osmoregulatory canals. Number of testes 22–40 (30.2, n=9) (30–40 in Douthitt 1915), distributed in single group antiporally and anteriorly to ovary. Poral testes reach level of poral margin of vitellarium or ovary, or poral longitudinal ventral canal (but not overlapping latter). No testes found lateral to antiporal longitudinal ventral canal (n=9). Testes overlap anterior and antiporal margins of ovary, being in contact with antiporal lobe of vitellarium in one specimen. Diameter of testes variable (0.035–0.110). Cirrus sac 0.12–0.20 (0.16, n=7) long in mature proglottids or 19–26% (n=3) of proglottid width, overlapping or extending across longitudinal ventral canal. Maximum length of cirrus sac in postmature proglottids 0.19–0.22 (n=3). Muscle layers of cirrus sac thin. Ductus cirri armed densely with minute spines in its distal part. Internal seminal vesicle occupying up to half of cirrus sac length when filled with sperm. External seminal vesicle slightly pedunculated, distinctly set off from vas deferens, covered by large, poorly-stained cells. Ovary coarsely lobed, 0.15–0.34 (0.24, n=6) wide or 33–39% (n=3) of proglottid width, positioned medially or slightly antiporally, not filling whole space between ventral longitudinal canals. Vitellarium asymmetrically bilobed or irregularly shaped, positioned medially or slightly porally with respect to midline of ovary and proglottid (index of asymmetry 0.46–0.49, n=3), overlapping markedly posterior part of ovary. Vagina 0.13–0.17 (0.15, n=7) long, usually somewhat shorter than cirrus sac (75–100%, n=3), slightly curved, running posteriorly or postero-ventrally to cirrus sac, set off from seminal receptacle by slight constriction. Internally, vagina formed by tube with distinct wall; vaginal lumen wide. Internal surface of vagina lined at least proximally with delicate hairs pointing distally (seen poorly in whole-mounts). Vaginal tube and internal surface of poral region of seminal receptacle covered by layer of large cells. Seminal receptacle 0.09–0.15 (0.11, n=7) in diameter in mature proglottids, spherical or subspherical, even before being filled with sperm. Seminal receptacle retains its shape in postmature proglottids, attaining diameter of 0.15–0.18 (n=3). Early uterus not seen in whole-mounts; in sectioned type material it appears as loose network of anastomosing tubes in anterior part of mature proglottids. Uterus in pregravid proglottids filling most of medulla with few large anterior, posterior and lateral sacculations or diverticula and relatively simple system of internal trabeculae. Genital ducts, sacculations and trabeculae disappear in fully gravid proglottids. Eggs 0.060–0.070 (0.066, n=5) long, spherical in surface view, ovoid in side view. Pyriform apparatus present. FIGURE. 2. Paranoplocephala primordialis from Tamiasciurus hudsonicus. A. scolex (Wyoming). B. Mature proglottid (Minnesota, reconstruction of sectioned type material; redrawn from Haukisalmi & Henttonen 2001. C. Terminal genital ducts (Minnesota, sectioned type material). D. Mature proglottid (Quebec). E. Pregravid uterus (Minnesota, sectioned type material). Scale-bars in mm. Remarks. Paranoplocephala primordialis was described from the red squirrel T. hudsonicus from Minnesota, U.S.A. (Douthitt 1915), and it has later been reported from Microtus and Myodes voles in various parts of North America (Table 1). However, we suggest that P. primordialis is a host-specific parasite of T. hudsonicus, because it is morphologically distinct from the P. primordialis -like species in voles (see below). In addition to the type region (Minnesota), P. primordialis has been found in T. hudsonicus from Wyoming (U.S.A.), Alberta, Saskatchewan and Quebec (Canada) (Table 1). However, P. primordialis was not found during an examination of ca. 50 red squirrels and 100 Arctic ground squirrels (Spermophilus parryii) in various parts of Alaska (unpublished BCP data). Also, P. primordialis -like cestodes were not found in the red squirrel or other sciurids in the North Central States of the U.S.A. (Ohio, Michigan, Illinois, Wisconsin, Minnesota; Rausch & Tiner 1948), or in the red squirrel or Abert's squirrel (Sciurus aberti) in New Mexico (Patrick & Wilson 1995).

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