Hymenolepididae Ariola, 1899

Sasaki, Mizuki, Anders, Jason Lee & Nakao, Minoru, 2021, Cestode fauna of murid and cricetid rodents in Hokkaido, Japan, with assignment of DNA barcodes, Species Diversity 26, pp. 255-272 : 259-260

Family Hymenolepididae Ariola, 1899 Genus Hymenolepis Weinland, 1858

1. Hymenolepis sp. 1

The adult tapeworms of Hymenolepis sp . 1 (the isolate numbers 18AK285 and 19 AK270 ) were found from Ap . speciosus in Asahikawa. The following description was made based on one specimen ( Fig. 3A, B ): Scolex 0.43 wide . Rostellum unarmed . Rostellar sac, 0.10 long by 0.08 wide . Suckers circular, four in number, 0.11–0.14 in diameter . Neck region not discernible . Mature proglottids much shorter in length than width, 0.26 long by 1.9 wide . Genital pore unilateral . Cirrus sac 0.22–0.29 long . Cirrus 0.03–0.04 long . Testes spherical, three in number in each mature proglottid, almost of equal size, 0.097–0.12 in diameter, arranged in straight line . Ovary lobed, 0.19 long by 0.60 wide . Vitelline gland lobed, 0.018 –0.027 long by 0.065–0.10 wide .

The genus Hymenolepis sensu stricto is characterized by a rudimentary unarmed rostellum and other defined morphological traits ( Haukisalmi et al. 2010a; Makarikov and Tkach 2013; Nkouawa et al. 2016). The following four species of Hymenolepis have been found from Apodemus mice in Eurasia: Hym. diminuta, Hym. Hibernia Montgomery, Montgomery, and Dunn, 1987 , Hym. pseudodiminuta , and Hymenolepis apodemi Makarikov and Tkach, 2013 ( Montgomery et al. 1987; Asakawa 1989; Tenora et al. 1994; Makarikov and Tkach 2013). A lengthy cirrus of mature proglottids (0.060 –0.076 mm in length) is distinctive of Hym. apodemi ( Makarikov and Tkach 2013) . Although Hym. diminuta and Hym. hibernia are quite similar to each other, the latter has a lateral bulge of each proglottid extending backward over adjacent proglottids ( Montgomery et al. 1987).

The present phylogenetic trees of 28S rDNA and cox 1 showed that our isolates from Hokkaido and the isolate of Hym. pseudodiminuta from Honshu ( Ishih et al. 2003) might be classified as Hym. hibernia ( Figs 2 , 4 ). The values of pairwise divergence of cox 1 sequences among 14 isolates of Hymenolepis sp. 1 from Hokkaido, Hym. pseudodiminuta from Honshu, and Hym. hibernia from Korea, Europe, Turkey ranged from 0.048 to 0 (mean=0.030). The maximum value was reduced to 0.029, when excluded the Turkish isolates.

Hymenolepis pseudodiminuta was discovered from Ap. argenteus in Honshu and Shikoku and from Ap. speciosus in Honshu, Kyushu and Hokkaido ( Tenora et al. 1994; Furuse et al. 2014). Hymenolepis pseudodiminuta is morphologically very similar to Hym. hibernia. The difference of host geographic range between the two species was considered to be important for their classification ( Tenora et al. 1994). Our molecular analysis demonstrated the identity between Hymenolepis sp. 1 and both Hym. pseudodiminuta and Hym. hibernia, suggesting that Hymenolepis sp. 1 and Hym. pseudodiminuta might be proposed to be a junior synonym of Hym. hibernia. However, we here refrain from proposing a synonymization of them because further morphological and ecological evaluations of these species are needed.

2. Hymenolepis sp. 2

The adult tapeworms of Hymenolepis sp. 2 (nos. JA173, JA175, JA220, JA244, and H22B) were found from Ap. speciosus and My. rufocanus in Otofuke. The specimens were unsuitable for morphological diagnosis. The phylogenetic trees of 28S rDNA and cox 1 confirmed that this unknown species belongs to Hymenolepis ( Figs 2 , 4 ). The cox 1 sequences of the five isolates were completely identical to one another. Further sample collections are needed to clarify whether this unknown species is Hym. apodemi or another new cryptic species.

Figures

Fig. 3. Adult tapeworms of Hymenolepis sp. 1, Arostrilepis tenuicirrosa, and Microsomacanthus sp. A, Scolex of Hymenolepis sp. 1; B, mature proglottids of Hymenolepis sp. 1; C, scolex of A. tenuicirrosa; D, mature proglottid of A. tenuicirrosa; E, gravid proglottid of A. tenuicirrosa; F, whole body of Microsomacanthus sp.; G, scolex of Microsomacanthus sp.; H, mature proglottids of Microsomacanthus sp. Scale bars: A, C, G, 200µm; B, D, 500µm; E, 1mm; F, 2mm; G, 100µm.

Fig. 2. A maximum likelihood phylogenetic tree of the families Hymenolepididae, Anoplocephalidae, Catenotaeniidae, and Davaineidae. The tree was made with sequences of 28S rDNA (1137 nucleotide sites) under the substitutional model GTR+G. The isolates of this study (19AK270, JA175, 19AK170, JA313, 19AK378, AMU, and Para33SI) are shown in bold face. The DNA accession number of each taxon is shown in parenthesis. Bootstrap percentages are shown on each node. Scale bar indicates the number of substitutions per nucleotide site. Dibothriocephalus nihonkaiensis (accession no. LC474508) was used as an outgroup taxon.

Fig. 4. A maximum-likelihood phylogenetic tree of the genus Hymenolepis. The tree was made with sequences of mitochondrial cox1 (456 nucleotide sites) under the substitutional model GTR+G+I. The isolates of this study (18AK285, 19AK270, H22B, JA173, JA175, JA220, and JA244) are shown in bold face. The DNA accession number of each taxon is shown in parenthesis. Rodentolepis nana (accession no. LC063187) was used as an outgroup taxon.