Variolepis cf. bilharzii ( Krabbe, 1869 )

Mariaux, Jean & Georgiev, Boyko B., 2020, Cestode parasites (Neodermata, Platyhelminthes) from Malaysian birds, with description of five new species, European Journal of Taxonomy 616, pp. 1-35 : 27-28

Variolepis cf. bilharzii ( Krabbe, 1869)

Figs 33–35 , Table 3

Material examined

MALAYSIA • 1 spec.; Selangor, University of Malaya’s Gombak Field Station ; 3.32° N, 101.77° E; 280–350 m a.s.l.; 2 Aug. 2010; partial COI sequence, Genbank MN 590293 ; MHNG-PLAT-121153 .

Host

Copsychus malabaricus (Scopoli, 1786) ( Passeriformes , Muscicapidae ).

Description

Worm with body of medium size, 7.5 mm long; maximum width 380 at level of last available pregravid proglottides. Strobila consisting of 73 proglottides. Proglottides craspedote, wider than long. Scolex poorly delineated from neck, 150 in diameter ( Fig. 33 ). Suckers muscular, rounded, 75–88 (82, n = 4) in diameter; base covered with well developed microtriches. Rostellar sac 104 × 74, wide, mostly glandular. Rostellum well-developed, 66 × 45, muscular, armed with a single row of 10 small cricetoid hooks, about 15 long. Hooks with strong guard and thin, reduced handles ( Fig. 34 ). Neck not well marked, 140 in diameter; proglottization distinct at about 280 behind posterior margin of suckers. Genital pores unilateral, dextral, situated at about 40% of lateral proglottis margin length. Ventral osmoregulatory canals 8–13 wide, connected posteriorly in each proglottis by transverse anastomosis. Dorsal osmoregulatory canals 4–5 wide. Genital ducts dorsal to osmoregulatory canals. Genital atrium narrow, 10–15 deep, infundibular, with wide orifice.

Testes 3 in number; large, up to 109 in diameter, situated posteriorly and basically on transverse line, although one or another can be located anterior to the two others. Small external seminal vesicle present, just proximal to cirrus-sac. Cirrus-sac, elongate, 112–134 × 25–33 (124 × 29, n = 11), crossing osmoregulatory canals. Discrete internal seminal vesicle present, in proximal quarter of cirrus-sac. Cirrus unarmed.

Vitellarium posterior to ovary, central, massive. Ovary antero-central, bi-winged with wings diverging posteriorly, compact but forming a few lobes in late development. Mehlis’ gland anterior to vitellarium. Vagina opened posteriorly to male pore and parallel, postero-ventrally to cirrus pouch. Seminal receptacle central and dorsal, between ovary wings, anterior to vitellarium, up to 74 in largest diameter ( Fig. 35 ).

Uterus starts its development in late mature proglottides as an antero-central sac, developing into a horseshoe-shaped saccular structure. Completely developed uterus and eggs not observed.

Remarks

Our material most closely matches the definition of Variolepis Spasskii & Spasskaya, 1954 . This genus has been treated very differently by various authors. Notably it has recently been put in synonymy with Wardium Mayhew, 1925 by Czaplinski (in Czaplinski & Vaucher 1994). This synonymy has, however, been widely considered as unjustified and Variolepis is now recognised as being valid ( Mariaux et al. 2017; Dimitrova et al. 2019).

The most widespread species of Variolepis is the type-species, V. farciminosa (Goeze, 1782) , that has been found on several continents and in a wide diversity of passerine hosts. Most of these contributions report substantial variations in the observed characters (see, e.g., Illescas Gómez & Gómez García 1984), casting some doubts on their conspecificity and possibly being indicative of a complex of species. A common character of “ V. farciminosa ” s. lat. is nevertheless the presence of relatively long (20 or more) rostellar hooks, that unambiguously differentiate it from our material. Nine more species of the genus are known from Passeriformes worldwide ( Schmidt 1986). We have summarized their available distinctive characters in Table 3 . Most differ from our material by their larger rostellar hook size and only V. planestici ( Mayhew, 1925) and V. bilharzii ( Krabbe, 1869) are comparable for that crucial character.

Variolepis planestici was described from an American robin by Mayhew (1925), unfortunately without some crucial details such as rostellar or cirrus-sac measurements. Despite its similar hooks, this species seem to differ from our material by having its testes clearly disposed in a triangle.

The original description of V. bilharzii is incomplete; however, Krabbe’s drawings show hooks with massive guards that are much longer than the blades ( Krabbe 1869: figs 228–229.). A later description by Joyeux & Baer (in Joyeux et al. 1928) from a West African drongo is the most complete to date but remains partial. The species was subsequently only found again by Johri (1935) in a crow from Myanmar. Interestingly, in his figure 4, Johri illustrates hooks of the same shape as shown by Krabbe. It is difficult to separate our material from V. bilharzii , although our specimen has a smaller scolex and suckers and a somewhat larger cirrus-sac. Furthermore V. bilharzii is described with testes in a triangular arrangement, but testes are mostly in a row in our material (although some variation is possible, see Fig. 35 ).

Globally, the characters available to differentiate our material and the two species discussed above are extremely limited and basically insufficient. Previously used arguments (e.g., Mayhew (1925) claimed a slight difference in hook shape for erecting V. planestici ) need to be critically evaluated with more material. As a consequence, it is very difficult to separate our material from both above-mentioned taxa, or indeed to separate them from each other. For now, we attribute our specimen to V. bilharzii , given its species range and diversity of hosts, which include East Asia and Muscicapidae . Due to priority, it is also the name that would apply to all these specimens in case they are eventually considered conspecific. A more definite conclusion would require additional specimens to assess their morphological variation and, in the case of the Malaysian material, fully gravid proglottides to observe the morphological characters of the eggs.

Figures

Figs 31–35. — 31–32. Ophryocotlyoides dasi Tandan & Singh, 1964. 31. Scolex with double crown of hooks, spinuous pseudoproboscis and armed suckers margins. 32. Mature proglottis, ventral view. — 33–35. Variolepis cf. bilharzii (Krabbe, 1869). 33. Scolex. 34. Rostellar hooks. 35. Mature proglottis. Scale bars: 31, 33 = 50 µm; 32 = 250 µm; 34 = 20 µm; 35 = 100 µm.