Paranoplocephala nearctica, Haukisalmi, Voitto & Henttonen, Heikki, 2007

Haukisalmi, Voitto & Henttonen, Heikki, 2007, A taxonomic revision of the Paranoplocephala primordialis (Douthitt) complex (Cestoda: Anoplocephalidae) in voles and squirrels, Zootaxa 1548, pp. 51-68 : 58-62

Paranoplocephala nearctica n. sp.

( Figs. 3–4 )

Type host: Myodes rutilus, Myomorpha , the northern red-backed vole.

Type locality: unnamed lake near North Fork of Koyukuk River, Gates of the Arctic National Park and Preserve ( GAAR), northern Alaska, U.S.A., 67o27'11.2"N, 150o51'00.2"W.

Site: Small intestine (duodenum or jejunum).

Deposited specimens: Holotype: MSB Endo 1 (field code AF 61624), from My. rutilus ( UAM 78325) collected on 23rd July 2002 at an unnamed lake near North Fork of Koyukuk River, Gates of the Arctic National Park and Preserve ( GAAR), northern Alaska, U.S.A. (67o27'11.2"N, 150o51'00.2"W). Collectors: H. Henttonen, K. Hildebrandt, J. Laakkonen and J. Niemimaa. Paratype: MSB Endo 2 (field code AF 59966), from My. rutilus ( UAM 79092), collected on 14th July 2002 at Agiak Lake, GAAR, Alaska (68o95'01.4"N, 152o57'36.2"W). Collectors as for the holotype. Voucher specimens: i) MSB Endo 4 (AF 59962), from My. rutilus ( UAM 79088), Agiak Lake, GAAR, Alaska, ii) MSB Endo 7 (AF 61179), from My. rutilus ( UAM 78871), Agiak Lake, GAAR, Alaska, iii) MSB Endo 11 (NK 124538), from My. rutilus, Dot Lake , Highway 2, eastern Alaska, iv) MSB Endo 12 (NK 124627), from My. rutilus, Dawson City , Yukon, Canada, v) MSB Endo 10 (IF 6991), from My. rutilus, Stikine River , British Columbia, Canada, vi) MSB Endo 8 (IF 6889), from My. gapperi, Stikine River , British Columbia, vii) MSB Endo 9 (IF 6941), from My. gapperi, Stikine River , British Columbia, viii) MSB Endo 3 (AF 49312), from Mi. longicaudus ( UAM 58405), Mt. Kathryn, Yukon-Charlie Rivers National Preserve, Alaska.

Description: Based on eleven specimens from My. rutilus from various localities in Alaska, northwestern British Columbia and western Yukon ( Tables 1 and 2).

Fully gravid strobila 65–104 (n=4) long; maximum width (0.75–1.50, 1.13, n=9) attained in pregravid or gravid proglottids. Number of proglottids ca. 300 (n=1). Proglottids craspedote, but velum short in wellrelaxed specimens. Length/width ratio of mature proglottids 0.25–0.57 (0.41, n=21), of gravid proglottids significantly higher (0.50–1.13 (0.79, n=22). Scolex simple, flat or rounded apically; width 0.44–0.55 (0.49, n=9). Suckers 0.16–0.23 (0.19, n=29) in diameter, directed antero-laterally, embedded in scolex. Neck 0.35– 0.75 (0.55, n=9) long, not clearly distinct from scolex, tapering posteriorly, minimum width (0.18–0.31, 0.23, n=9) attained in region where segmentation first visible.

Genital pores unilateral (3/11) or with 1–12 alternations per strobila (8/11), opening in posterior third of proglottid margin in mature proglottids.

Ventral longitudinal osmoregulatory canals 0.02–0.07 (0.037, n=34) wide, transverse commissures of ventral canals poorly visible. Dorsal longitudinal osmoregulatory canals 0.01–0.02 wide, lateral to ventral longitudinal canals or partly overlapping them. Genital ducts passing dorsally to longitudinal osmoregulatory canals.

Number of testes 19–40 (27.4, n=18), distributed in single group antiporally and anteriorly to ovary. Poral testes reach level of poral margin of ovary or poral longitudinal ventral canal (but not overlapping latter). From 0 to 6 (1.4, n=18) testes positioned lateral to antiporal longitudinal ventral canal. Testes overlap anterior and antiporal margins of ovary, being usually in contact with antiporal lobe of vitellarium. Diameter of testes 0.05–0.09, large relative to proglottid size. Cirrus sac 0.13–0.28 (0.21, n=24) long in mature proglottids or 23–40% (29%, n=24) of proglottid width, usually extending across longitudinal ventral canal. Maximum length of cirrus sac 0.22–0.29 (0.26, n=10) in postmature proglottids. Muscle layers of cirrus sac thin. Ductus cirri armed densely with minute spines in its distal part. Internal seminal vesicle initially rounded, occupying up to 1/2 of cirrus sac length when filled with sperm. External seminal vesicle pedunculated or slightly coiled, distinctly set off from vas deferens, covered by large, poorly-stained cells.

Ovary coarsely lobed, large, 0.18–0.51 (0.32, n=23) wide and 0.12–0.26 (0.20, n=21) long in mature proglottids or 33–62% (44%, n=23) of proglottid width, covering whole space between ventral longitudinal canals and sometimes overlapping them. Vitellarium asymmetrically bilobed or irregularly shaped, usually positioned medially with respect to midline of ovary and proglottid (index of asymmetry 0.47–0.61, 0.51, n=24), overlapping markedly posterior part of ovary. Mehlis' gland positioned between lobes of vitellarium or anterior to it. Vagina 0.09–0.20 (0.15, n=23) long and 0.02–0.06 (0.038, n=15) wide, shorter than cirrus sac (55–88%, 71%, n=23), slightly curved, running posteriorly, postero-ventrally or ventrally to cirrus sac, distinctly set off from seminal receptacle. Internally, vagina formed by distinct, thin-walled tube, lumen of which widens distally. Internal surface of vagina lined with delicate hairs at least in its proximal half. Vaginal tube covered by layer of large cells; this layer merges with cell layer surrounding genital atrium. Seminal receptacle subspherical (before being filled with sperm), 0.08–0.19 (0.13, n=21) in diameter in mature proglottids. Seminal receptacle retains its shape in postmature proglottids, reaching maximum size of 0.15–0.32 (0.225, n=9). Uterus appears in early mature proglottids as loose, delicate reticulum ventral to testes and other organs and extending across longitudinal osmoregulatory canals bilaterally. Lateral margins of early uterus undefined, slightly wider than or as wide as middle part. Uterus in pregravid proglottids filling most of medulla with few irregular anterior, posterior and lateral sacculations or diverticula and numerous internal trabeculae. Genital ducts, sacculations and trabeculae disappear in fully gravid proglottids. Eggs 0.041–0.062 (0.0508, n=34) long, spherical in surface view, ovoid in side view. Pyriform apparatus present.

Remarks. Cestodes from My. gapperi were metrically very similar to those from My. rutilus . All quantitative features based on multiple measurements overlapped and no statistical differences were observed between measurements from the two host species (Table 2). In addition, no consistent differences were observed in the morphology of the genital ducts or other qualitative features ( Figs. 3–4 ). We conclude that the studied specimens from My. gapperi are conspecific with those from My. rutilus .

Paranoplocephala communis from My. gapperi has been considered either a synonym of P. primordialis (see Baer 1927; Rausch & Schiller 1949; Spasskii 1951) or a species inquirenda ( Tenora et al. 1986). We favor the latter view, because the original material consisted of contracted, sectioned fragments only. In addition, the examination of the existing type material of P. communis (one slide: USNPC 49514) showed that its longitudinal ventral canals are conspicuously wider than in the material described and illustrated by Douthitt (1915). Wide osmoregulatory canals are characteristic for the Nearctic Paranoplocephala macrocephala (see Douthitt 1915; Haukisalmi & Henttonen 2003), suggesting that the type material of P. communis may have included two species (see also Tenora et al. 1986).

Paranoplocephala nearctica n. sp. differs from P. primordialis by the more elongate shape of gravid proglottids, longer cirrus sac (maximum length), relatively larger vitellarium and perhaps also by the relatively larger ovary in the former species (Table 2). The ovary of P. nearctica n. sp. fills the whole space between the longitudinal ventral canals (often overlapping them), whereas the ovary of P. primordialis does not. Douthitt (1915) mentioned that in the type material of P. primordialis (from T. hudsonicus ) the seminal receptacle does not overlap the ventral longitudinal canal, which seemed to separate P. primordialis from the related species known by then. A corresponding difference between P. primordialis and P. nearctica n. sp. is seen in the present study (cf. Figs. 2 and 3), although there is some variability within the latter species in this respect. In addition, the eggs of P. nearctica n. sp. appear to be smaller than those of P. primordialis (Table 2). However, the egg size for P. primordialis may be biased, because it is based on a single cestode specimen (USNPC 47801). Douthitt (1915) did not give egg dimensions for P. primordialis (or P. communis ), because his material did not include fully gravid specimens.

Morphological differences between P. n e a rc t i c a n. sp. and P. alaskensis n. sp. are described in the Remarks-section of the latter species (below). Of the other species, P. nearctica n. sp. resembles Paranoplocephala bairdi (Schad) (from Phenacomys and Arborimus ), Paranoplocephala fellmani Haukisalmi & Henttonen (from Lemmus ), Paranoplocephala arctica (Rausch) sensu Haukisalmi et al. 2001 , and Paranoplocephala nordenskioeldi Haukisalmi, Wickström, Hantula & Henttonen (the latter two from Dicrostonyx ), all of which occur in North America ( P. fellmani and P. nordenskioeldi also in the northern parts of Eurasia). They all have a small scolex, unilateral or infrequently alternating genital pores and basically similar distribution of testes (antiporal and anterior to ovary). The main morphometric features of the four species compared here with P. n e a rc t i c a n. sp. have been summarized by Haukisalmi et al. (2005).

Paranoplocephala bairdi has a significantly longer body, smaller scolex and suckers, and wider ventral longitudinal canals than P. nearctica n. sp. (see Haukisalmi et al. 2005). Paranoplocephala arctica has a wider body, smaller scolex and suckers, thinner neck, more numerous testes (including the antiporal ones), larger cirrus sac and seminal receptacle, and larger eggs than P. nearctica n. sp. (see Haukisalmi et al. 2001). Paranoplocephala fellmani can be best separated from P. nearctica n. sp. by its longer and slender cirrus sac, and smaller seminal receptacle. Additionally, the length/width ratio of gravid proglottids tends to be lower and the number of antiporal testes tends to be higher in P. fellmani than in P. nearctica n. sp. (see Haukisalmi & Henttonen 2001). Paranoplocephala nordenskioeldi has a wider body and thinner neck than P. n e a rc t i c a n. sp. and a longer seminal receptacle of different shape (elongated in P. nordenskioeldi ) (see Haukisalmi et al. 2001).

Paranoplocephala nearctica n. sp. and other P. primordialis -like species also resemble Paranoplocephala montana (Kirshenblat) , described from voles of the Transcaucasus ( Kirshenblat 1941). However, the original description of the latter species is in many ways inadequate, there are no redescriptions, and no type material exists. Paranoplocephala montana is therefore treated here as a species inquirenda.

The single available specimen from Microtus longicaudus ( Fig. 6 ) was identified as P. nearctica n. sp., because most of its measurements were closer to the mean values of P. nearctica n. sp. than those of P. alaskensis n. sp.

Figures

FIGURE 3. Paranoplocephala nearctica n. sp. A. scolex (ex. Myodes rutilus, Alaska). B. Scolex (ex. Myodes gapperi, British Columbia). C. Mature proglottid (ex. My. rutilus, Alaska). D. Mature proglottid (ex. My. rutilus, Alaska). E. Mature proglottid (ex. My. gapperi, Quebec). Scale-bars in mm.

FIGURE 4. Paranoplocephala nearctica n. sp. A. early uterus (ex. Myodes rutilus, Alaska). B. pregravid uterus (ex. My. rutilus, Alaska). C. Gravid proglottids (ex. My. rutilus, Alaska). D. Gravid proglottids (ex. Myodes gapperi, British Columbia). Scale-bars in mm.

FIGURE 6. A. Scolex of Paranoplocephala nearctica n. sp. (ex. Microtus longicaudus, Alaska). B. Scolex of Paranoplocephala sp. (ex. Microtus oeconomus, Alaska). C. Mature proglottid of Paranoplocephala sp. (ex. Mi. oeconomus, Alaska). D. Mature proglottid of P. nearctica n. sp. (ex. Mi. longicaudus, Alaska). E. Gravid proglottids of Paranoplocephala sp. (ex. Mi. oeconomus, Alaska). Scale-bars in mm.