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 : 262-263

Family Hymenolepididae Ariola, 1899

Genus Microsomacanthus Lopez-Neyra, 1942 4. Microsomacanthus sp.

The adult tapeworms of Microsomacanthus sp. (nos. 19AK212, JA313 , Para09, Para15, Para18, and Para19) were found from Ap. speciosus in Asahikawa and Obihiro. The following description was made based on one specimen ( Fig. 3F–H ): Whole body tiny, without gravid proglottids, 16 long by 1.2 in maximum width. Scolex 0.25 in maximum width. Rostellum 0.18 long, armed with 10 hooks, 0.022 – 0.025 in length. Suckers circular, four in number, 0.09–0.10 in diameter. Mature proglottids much longer in width, 0.028 in length by 0.49 in width. Genital pore unilateral. Testes oval to pyriform, three in number, situated triangularly, 0.13–0.15 long by 0.49–0.55 wide. Poral testis separated from antiporal testes by female gonads. Ovary amorphous, 0.13–0.15 long by 0.25–0.28 wide, positioned in center of proglottid. Small vitellarium unlobed, postovarian.

All the six isolates of Microsomacanthus sp. were subjected to DNA sequencing of cox 1. The resultant sequences were highly homogeneous (mean pairwise divergence=0.004). A BLAST homology search could not detect any sequences similar to them. In the case of 28S rDNA, the unknown species showed 99.6% similarity (1360 out of 1365 nucleotides identical) to Microsomacanthus crenatus (Goeze, 1782) from Apodemus sylvaticus ( Linnaeus, 1758) in Croatia (database accession no. GU166246 ). Haukisalmi et al. (2010a) treated this isolate ( M. crenatus in DNA databases) as “ Hymenolepis ” muris-sylvatici . A 28S rDNA-based phylogenetic tree supports that the unknown species belongs to Microsomacanthus (see the isolate JA 313 in Fig. 2 ). It is highly probable that “ Hymenolepis ” muris-sylvatici or Microsomacanthus murissylvatici (Rudolphi, 1819) is identical to M. crenatus ( Czaplinski and Vaucher 1994; Tenora 2004).

Most members of Microsomacanthus exclusively use birds as definitive hosts ( Yamaguti 1959; Czaplinski and Vaucher 1994). However, M. crenatus have been recorded exceptionally from Apodemus mice in Europe ( Prokopič 1967; Behnke et al. 1999; Tenora 2004; Klimpel et al. 2007). Such a distant host-switching suggests a possibility that the rodent-related species belong to another genus. The confirmation of this hypothesis is challenging, because the present DNA databases lack the 28S rDNA and cox 1 sequences of Microsomacanthus from birds.

Our specimen is morphologically similar to M. murissilvatici , particularly in the sizes of strobila, scolex and suckers, when compared with the data of previous reports ( Baer 1931; Prokopič 1967). A preliminary phylogeny of 28S rDNA ( Haukisalmi et al. 2010a) suggests that “ Hymenolepis ” muris-sylvatici is sister to Rodentolepis evaginata (Barker and Andrews, 1915) . Molecular phylogenetic assessments and subsequent taxonomic revisions are required for the rodent-related species of Microsomacanthus .

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.