Anoplocephaloides Baer 1923

Anoplocephaloides Baer, 1923

(Fig. 1)

Diagnosis: Strobila short and wide. Scolex large with prominent suckers directed anteriorly. Neck (unsegmented region) usually absent. Proglottides craspedote, much wider than long; velum curved posteriorly. Genitalia single. Genital pores unilateral, positioned slightly anterior to middle of proglottis margin. Genital atrium weak; genital papilla absent. Ventral osmoregulatory canals narrow, strongly arched. Genital ducts cross osmoregulatory canals dorsally. Internal and external seminal vesicles present. External seminal vesicle large in postmature proglottides, attaining or approaching size of cirrus sac. Cirrus sac short, barely extending across ventral longitudinal canal. Retractor muscle of cirrus sac absent. Testes arranged in single transverse group in antiporal part of proglottis, usually not extending beyond antiporal ventral longitudinal canal. Ovary large relative to proglottis size, transverse, more or less poral, sparsely lobed. Vagina short, not extending across ventral longitudinal canal; enters genital atrium ventral or postero-ventral to cirrus sac. Early uterus transverse tube in anterior part of proglottis, ventral to testes, extending ventrally and bilaterally across longitudinal osmoregulatory canals; poral end terminates anterior to cirrus sac and external seminal vesicle or partly overlaps them. Fully developed (pregravid) uterus sparsely sacculated with wide anterior and posterior sacculi that are pressed against adjacent sacculi throughout their development; distinct transverse trunk absent. Pyriform apparatus present. Female reproductive organs mature slightly earlier than male organs; testes persist after resorption of female glands overlapping developing uterus. Parasitic in geomyid (type hosts) and cricetid (Arvicolinae) rodents, exceptionally in other rodents. Type species: A. infrequens (Douthitt, 1915) Baer, 1923 [syns. Anoplocephala infrequens Douthitt, 1915, Paranoplocephala infrequens (Douthitt, 1915) Baer, 1923]; cotypes USNPC 49515 and 49520 from the plains pocket gopher Geomys bursarius (Shaw). Other species: A. dentata (Galli-Valerio, 1905) Rausch, 1976 [syns. Anoplocephala dentata Galli-Valerio, 1905, Paranoplocephala dentata (Galli-Valerio, 1905) Spasskii, 1956], A. troeschi (Rausch, 1946) Rausch, 1976 (syn. Paranoplocephala troeschi Rausch, 1946), A. lemmi (Rausch, 1952) Rausch, 1976 (syn. Paranoplocephala lemmi Rausch, 1952), A. kontrimavichusi Rausch, 1976, A. dentatoides Sato, Kamiya, Tenora & Kamiya, 1993 and A. bulmeri Haukisalmi & Eckerlin, 2009. Notice that A. dentata -like cestodes include at least 6 more or less cryptic species, as determined by molecular methods (Haukisalmi et al. 2009).

Remarks. The genus Anoplocephaloides is restricted to a monophyletic group of species with the above features (see also Haukisalmi et al. 2009). Anoplocephaloides differs unequivocally from the other genera considered here with respect to the transverse, longitudinal and/or dorso-ventral position of the early uterus, except Microcephaloides, Paranoplocephaloides, Hokkaidocephala and Gallegoides Tenora & Mas-Coma, 1978 (Table 2). Anoplocephaloides differs markedly from Microcephaloides by its shorter and wider body, much larger scolex with anteriorly directed suckers, absence of a neck, posteriorly curved velum, slightly anterior position of the genital openings and antiporal extent of the testes (see also Haukisalmi et al. 2008b).

Anoplocephaloides can be unequivocally separated from Paranoplocephaloides by its short, ”wedgeshaped” body, larger scolex, shape of the velum, position of the genital openings and unilateral genital pores (see also Gulyaev 1996). In addition to the differences in the direction of the suckers, shape of the velum and lateral position of the genital openings, Hokkaidocephala differs from Anoplocephaloides (and other genera) by the peculiar structure of its fully developed (pregravid) uterus (see also Haukisalmi et al. 2008a). Gallegoides has antiporal and anterior testes positioned mainly in the posterior part of the proglottis and alternating genital pores, which differentiates it unambiguously from Anoplocephaloides.

Anoplocephaloides lemmi differs from the other species of Anoplocephaloides by its larger body with more numerous proglottides, more elongated anterior strobila and presence of a neck (Rausch 1976 and the present study). A recent molecular phylogenetic study shows unequivocally that A. lemmi forms a monophyletic group with the other Anoplocephaloides species (Haukisalmi et al. 2009). In the phylogram based on sequences of the partial cytochrome I (COI) gene, A. lemmi formed the basal lineage within Anoplocephaloides, which seems to provide grounds for the separation of A. lemmi at the generic level. However, the phylogram based on sequences of the 28S ribosomal RNA, which is a more conservative region than COI, placed A. lemmi and A. kontrimavichusi as independent basal lineages within Anoplocephaloides. Because the phylogenetic relationships within Anoplocephaloides are still partly obscure and because A. lemmi confirms morphologically with the other Anoplocephaloides species (with a few deviations), it is retained in this genus.

Anoplocephaloides spp., including A. lemmi, all inhabit the posterior small intestine, caecum or junction between them, in which respect they differ from all other species in the arvicoline clade of cestodes and phylogenetically related taxa.

FIGURE. 1. Anoplocephaloides spp. A. Strobila of A. cf. dentata from Microtus arvalis (scale-bar 1.0 mm). B. Mature proglottis of A. infrequens (cotype) from Geomys bursarius (scale-bar 0.50 mm). C, D. Development of uterus in A. cf. dentata from Microtus pennsylvanicus (scale-bars 0.30 mm). E. Male ducts of A. cf. dentata from Microtus miurus (scale-bar 0.20 mm). F. Female ducts and early uterus of A. cf. dentata from M. miurus (scale-bar 0.20 mm).