Arostrilepis cooki Makarikov, Galbreath & Hoberg, 2013, sp. n.
Creators: name: Makarikov, Arseny A.
name: Galbreath, Kurt E.
name: Hoberg, Eric P.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Platyhelminthes
Cestoda
Cyclophyllidea
Hymenolepididae
Arostrilepis
Arostrilepis cooki

description: Arostrilepis cooki sp. n.
(Figs. 4, 5)
Type host: Myodes gapperi (Vigors) (Rodentia: Cricetidae: Arvicolinae).
Other hosts: Currently unknown.
Type locality: Near Meziadin Junction, British Columbia, Canada (56o21’55”N, 129o16’28”W).
Other localities: Taft Creek, British Columbia (56o29’46”N, 129o25’31”W); near Bell II, British Columbia, south side Deltaic Creek (ca., 56o32’38”N, 129o32’39”W); Pattee Canyon, Missoula Co., Montana, USA (46o48’N, 113o57’W).
Type material: Holotype MSB Para 1244 (field number IF 6750/ cyt- b sequence) from type host and locality by A.M. Runck et al., 9 June 2003. Paratypes from type host species: MSB 1245 (IF 6751/ cyt- b sequence) by A.M. Runck et al., at type locality, 9 June 2003; MSB 1249–1252 (IF 6830 C2; 6830 C3; 6830 C4; 6830 C6/ cyt- b sequence) by A.M. Runck et al., at Taft Creek, British Columbia, 14 June 2003; MSB 1217 (JMK 02-10), collected by J. M. Kinsella at Pattee Canyon, Montana, 10 October 2002; MSB 1246–1248 (IF 6827 C1; 6827 C2; 6827 C3) by A. Runck et al., at Bell II, British Columbia, 14 June 2003.
Symbiotype: Myodes gapperi (IF 6750) at type locality, skull and skeleton in MSB Mammalogy Division.
Description: Based on 8 specimens. Fully developed strobila up to 150 mm long, with maximum width at postmature or pregravid gravid proglottides, 1.25–1.4 mm. Strobila flat, consisting of about 850 craspedote proglottides. Scolex slightly compressed dorso-ventrally, 280–372 (324, n = 4) wide, clearly wider than neck. Suckers unarmed, ovoid in surface view, 162–238 × 124–195 (190 × 161, n = 8), with thin walls, prominent (Fig. 4 A, B). Rhynchus and rostellar apparatus absent. Neck relatively long and narrow, 160–200 (178, n = 8) wide.
Two pairs of osmoregulatory canals, without transverse anastomoses. Dorsal osmoregulatory canals thin, 0.5–2 (1.2, n = 10) wide, situated predominantly in same sagittal plane as ventral canals. Ventral osmoregulatory canals 30–65 (44, n = 15) wide. Position of dorsal osmoregulatory canals not always constant; loops may be situated laterally to ventral canals. Genital pores unilateral, dextral. Genital ducts usually pass dorsally to longitudinal osmoregulatory canals, position of genital ducts between osmoregulatory canals within single strobila appears rarely (Fig. 4 C, D). Development of proglottides gradual, protandrous. Strobilar part containing juvenile proglottides without external segmentation; proglottides become externally distinct at level of premature part of strobila.
Mature proglottides 120–275 × 680–1040 (198 × 785, n = 12), transversely elongate, trapeziform (Fig. 4 C, D). Testes relatively large, usually three in number, almost of equal size, 115–175 × 85–125 (135 × 96, n = 25), round or oval, commonly situated in triangle; poral testis separated from two antiporal testes by female gonads. Arrangement of testes may vary (from triangle with flat angle to linear). Cirrus-sac relatively short, 190–218 × 35–48 (205 × 42, n = 15), with well-developed external muscular layers, commonly extends across ventral longitudinal canal (Figs. 4 D, 5C). Genital atrium simple, infundibular, deep, opens laterally about middle or slightly anterior of lateral proglottis margin. Cirrus 88–109 (98, n = 16) long, conical, with relatively wide basal region, 19–24 (21, n = 16) in diameter, and narrow distal region, 8–14 (11, n = 16) in diameter; armed along entire length with relatively large (up to 3.3–4 long) rosethorn-shaped spines (Fig. 5 A). Internal seminal vesicle with circular musculature, ovoid, 85–120 × 28–40 (95 × 33, n = 15), shorter than half of cirrus-sac length (Figs. 4 D, 5C). External seminal vesicle transversely elongate, 117–171 × 65–103 (151 × 78, n = 15), clearly outlined from vas deferens, slightly larger than seminal receptacle.
Ovary 305–410 (329, n = 20) wide, median, fan-shaped, irregularly lobed, ventral to male genital organs, occupying substantial part of median field, slightly overlapping testes (Fig. 4 D). Vitellarium 60–117 × 115–172 (91 × 153, n = 20), postovarian, median, scarcely lobed. Vagina tubular, clearly distinct from seminal receptacle; ventral to cirrus-sac. Distal part of vagina 92–111 × 9–19 (100 × 13, n = 10), thick-walled, covered externally by dense layer of intensely stained cells; proximal part of vagina infundibular (Fig. 5 C). Conductive part of vagina 110–132 × 10–27 (122 × 17, n = 10), thin-walled, vastly varying in diameter depending on degree of distention with sperm. Seminal receptacle relatively small, transversely elongate, 80–122 × 40–77 (100 × 51, n = 14).
Uterus appears as complex of fine-walled anastomosing tubes of varying length and diameter, positioned ventrally to other organs. With development of proglottides, tubular structures increase in width and uterus becomes labyrinthine. Testes remain in postmature and pregravid proglottides; cirrus-sac and vagina persist in gravid proglottides. Gravid proglottides transversely elongate, 185–360 × 810–1330 (261 × 1107, n = 10). Fully developed uterus labyrinthine, occupying entire median field, extending bilaterally beyond longitudinal osmoregulatory canals (Fig. 5 D). Uterus contains numerous (up to 1100) eggs. Eggs 31–38 × 58–72, elliptic, with thin outer coat (Fig. 5 B); oncosphere 13–17 × 18–23. Embryophore fusiform, 17–20 × 40–48, with straight polar processes. Embryonic hooks small, 7.5–8.3 long.
Etymology: This species has been named in honor of Joseph A. Cook in recognition of contributions in understanding rodent systematics and biogeography, and innovative explorations of host-parasite associations among arvicoline rodents.
Remarks: Arostrilepis cooki sp. n. is distinguished from congeners by the length and shape of the cirrus (Table 2). In specimens of A. cooki the cirrus is longer in comparison to A. beringiensis, A. microtis, A. tenuicirrosa, A. gulyaevi, A. mariettavogeae and A. schilleri. The cirrus is armed with relatively large rosethornshaped spines and has a conical form; these features distinguish A. cooki from A. beringiensis, A. intermedia, A. janickii and A. schilleri, which have cylindrical cirri, and from A. microtis, A. tenuicirrosa and A. gulyaevi, in which the cirri have a conical basal region and cylindrical distal region. Compared to A. cooki, the cirrus of A. tenuicirrosa is armed with relatively small needle-shaped spines. The form and the length of the cirrus of A. cooki are most similar to those of A. macrocirrosa, but in specimens of the former the cirrus is narrower in the basal region (Figs. 11, 12). Arostrilepis cooki is characterized by a relatively narrow strobila. The cirrus-sac is shorter than that in A. horrida and A. microtis but larger than in A. beringiensis, A. janickii, A. mariettavogeae and A. schilleri. The ovary is narrower relative to those in A. horrida, A. microtis and A. gulyaevi. The scolex and the suckers are larger in comparison to A. janickii. The egg and oncosphere are large relative to those in A. horrida, A. microtis and A. janickii (see Table 2). The proximal end of the cirrus-sac in hermaphroditic mature proglottides overlaps the ventral longitudinal osmoregulatory canal. This species can be distinguished from A. beringiensis as its testes are arranged in a triangle; in the latter species, the testes form a flat angle or are situated in one row. Similarly, the testes form one row in A. microtis and A. mariettavogeae. Furthermore, the external seminal vesicle is larger than the seminal receptacle, the gravid proglottides are transversely elongate, and the polar processes of the embryophore are straight in A. cooki. This species is a specific parasite of red-backed voles (Myodes) from North America.
description: Published as part of Makarikov, Arseny A., Galbreath, Kurt E. & Hoberg, Eric P., 2013, Parasite diversity at the Holarctic nexus: species of Arostrilepis (Eucestoda: Hymenolepididae) in voles and lemmings (Cricetidae: Arvicolinae) from greater Beringia, pp. 401-439 in Zootaxa 3608 (6) on pages 412-414, DOI: 10.11646/zootaxa.3608.6.1, http://zenodo.org/record/216055