Sobolevitaenia anthusi

Sobolevitaenia anthusi (Spasskaya, 1958)

Figs 4–7

MALAYSIA • 2 specs (in fragments, one without gravid proglottides); Selangor, University of Malaya’s Gombak Field Station; 3.32° N, 101.77° E; 280–350 m a.s.l.; 11Aug. 2010; no COI sequence successfully retrieved; MHNG-PLAT-121462.

Motacilla cinerea Tunstall, 1871 (Passeriformes, Motacillidae).

Body of small size, with length up to 25.5 mm and maximum width 720 at level of gravid proglottides; consisting of at least 101 proglottides. Proglottides craspedote, initially wider than long but rapidly elongating; gravid proglottides up to 2.5 times as long as wide. Scolex elongate, fragile, 112–150 in diameter (Fig. 4). Suckers rounded, 82–95 (89, n = 8) in diameter, weakly muscular, with internal surface covered by small shovel-shaped spines, ca 2.5 wide (Fig. 5). Rostellar sac large, filling most of scolex volume, cylindrical, passing beyond level of posterior margin of suckers, 175–185 × 77. Rostellum large, well-delineated and weakly muscular, 150–155 × 70–72. Hooks 20 in number, in 2 poorly delineated rows; each hook with short blade and guard and long handle (Fig. 6). Anterior hooks 30–33 (32, n = 6) long. Posterior hooks 26.5–30 (27.5, n = 9) long. Proglottization distinct at 138–160 from posterior margin of suckers. Genital pores situated anteriorly at 20–25% of length of lateral proglottis margin, irregularly alternating in very short series; no more than 3 consecutive pores observed on one side. Ventral osmoregulatory canals up to 20 wide, more commonly 5–10 wide, connected posteriorly in each proglottis by transverse anastomosis. Dorsal osmoregulatory canals narrow, 2–4 wide. Genital ducts passing between osmoregulatory canals. Genital atrium small, unremarkable.

Testes 17–21 (18.5, n = 23) in number; in 2 layers, in one continuous posterior field, not overlapping osmoregulatory canals and rarely overlapping posterior lobes of ovary and vitellarium (Fig. 7). External vas deferens coiled anteriorly, overlapping proximal extremity of cirrus-sac. Cirrus-sac elongate, strong and very large, 183–228 × 35–45 (201 × 41, n = 14), often slightly bent anteriorly at mid-length, reaching or extending beyond middle of proglottis. Internal vas deferens forming several coils, mostly in proximal third of cirrus-sac. Cirrus armed with well-developed spines of various sizes; spines smaller proximally and less numerous, stronger and larger distally, up to 5 long.

Vitellarium central, compact, globulous, particularly large, 70–110 × 90–140 (86 × 109, n = 7) in late mature proglottides. Ovary antero-central, bi-alate, longitudinally elongate, large; antiporal wing slightly larger than poral wing; not overlapping longitudinal osmoregulatory canals. Mehlis’ gland globular, immediately anterior to vitellarium. Seminal receptacle oval, central, dorsally overlapping ovary and, possibly, vitellarium in part, reaching up to 225 × 175 in pregravid proglottides. Vagina opens posterior to male pore, well-marked with compact cellular sheath over its entire length, straight and transverse, parallel to cirrus-sac up to two thirds of its length, then markedly bent posteriorly, sometimes partially overlapping cirrus-sac dorsally (Fig. 7).

Uterus starts its development as a diffuse reticulum, progressively forming numerous small lobes and occupying entire median field; crossing osmoregulatory canals and extending in lateral fields. Uterus eventually becoming multisaccular, almost labyrinthine. Embryophores thick. Oncospheres oval, 26– 31 × 20–23 (28 × 21, n = 15). Embryonic hooks 10 long.

This material presents all the characters of the genus Sobolevitaenia, a genus found in various passerines, including Motacillidae, that we recently discussed in detail (Mariaux & Georgiev 2018b). In that work, we presented a summary of the main metrical and meristic characters of the 17 known species of the genus. Most of them differ obviously from the present material because of their (mostly larger) hook length, number of testes or cirrus-sac length.

The most similar taxa are the type-species S. anthusi (Spasskaya, 1958) and its possible synonym S. orientalis Spasskii & Konovalov, 1969, which are found in various Motacillidae, rarely in other passerines, in the Palaearctic (Spasskaya & Spasskii 1977). Although some variation is known for this taxon, S. anthusi shows a rostellar armature and number of testes similar to the present material. It differs, however, essentially by having a shorter cirrus-sac (that also has a more limited extension across the proglottis), a longer rostellar sac, and a shorter rostellum. Its strobila is also shorter, not exceeding 15 mm (Spasskaya & Spasskii 1977). Sobolevitaenia orientalis has a different subset of differentiating characters, including a larger scolex, a shorter rostellar sac and slightly larger posterior hooks.

Finally, S. (?) borealis (Krabbe, 1869) also show characteristics similar to the present material. However, besides its very different hosts (Calcariidae) and distribution (Greenland), this poorly known taxon also has a larger scolex, only 18 rostellar hooks and shorter posterior hooks (according to Baer 1956).

The status of S. anthusi as a single species or a complex of similar species, and its possible synonymy with S. orientalis, remains unclear. Our material differs slightly from both original descriptions but would be included in the global variation of both taxa taken together. In addition, S. anthusi has been reported with significant morphological variation across its range that extends at least along the entire north coast of Russia and south to Tajikistan and Tuva. Those elements may be indicative of a complex of species, but for now we will take the cautious option of placing our material in S. anthusi sensu Spasskaya & Spasskii (1977).