Arctocestus

Arctocestus n. g.

(Fig. 13)

Etymology. The name of the new genus refers to the Arctic distribution of A. serratus and its hosts, Dicrostonyx spp. “ Arctocestus ” is masculine.

Diagnosis. Strobila of moderate dimensions. Scolex small, distinctly separate from neck. Suckers directed laterally or antero-laterally. Neck narrow (absolutely and relative to scolex width), of variable length. Length/width ratio of mature proglottids ca. 25%. Proglottids craspedote, with pronounced, protruding velum, giving strobila characteristic serrate appearance. Genital pores unilateral or infrequently (and irregularly) alternating. Genital ducts pass dorsal to longitudinal osmoregulatory canals. Ventral longitudinal osmoregulatory canals wide. Testes antiporal, most poral testes may reach midline of proglottid, i.e. level of antiporal lobe or middle of vitellarium. Several testes regularly positioned lateral to antiporal ventral longitudinal canal. Testes slightly overlapping ovary. Cirrus sac long and wide, with prominent external muscle layers, usually extending markedly across ventral longitudinal canal. Vagina tubiform, slightly shorter than cirrus sac, usually overlapping ventral longitudinal canal. Seminal receptacle pyriform or irregularly ovoid. Ovary median or slightly poral, extends to ventral longitudinal canal porally, but not antiporally. Vitellarium slightly antiporal with respect to ovary. Early uterus reticulated, anterior, ventral to other organs and extending across longitudinal canals bilaterally; lateral parts distinctly widened posteriorly. In collared lemmings, Dicrostonyx spp. (Cricetidae: Arvicolinae) in Arctic Eurasia and North America.

Type species: A. serratus (Haukisalmi & Henttonen, 2000) n. comb.

Paranoplocephala serrata Haukisalmi & Henttonen, 2000

Holotype of A. serratus: USNPC 88363.

Remarks. Arctocestus is compared with Rauschoides, Eurotaenia, Douthittia and Lemminia, all of which have an absolutely and relatively narrow neck, medium/long vagina (relative to the cirrus-sac length) and ovoid/ pyriform (not elongated) seminal receptacle. Arctocestus differs from all the latter genera in its distinctive (serrated) proglottid shape, transversely more elongated proglottids and less extensive distribution of testes in the poral part of the proglottid. In addition, Arctocestus has more numerous testes lateral to the antiporal ventral canal than Eurotaenia, Douthittia and Lemminia.

Arctocestus serratus shows phylogenetic affinity with Rauschoides in nad1 data (99%) and concatenated data (94%), but not in the cox1 data; in the latter it has an unresolved basal position. However, the pronounced morphological differences and high genetic divergence between Arctocestus and Rauschoides favour their status as independent genera.