Australotaenia hobbsi, Chambrier & Scholz, 2024

Chambrier, Alain De & Scholz, Tomáš, 2024, A new species of Australotaenia (Cestoda: Proteocephalidae) from a hylid frog in Australia, Zootaxa 5458 (3), pp. 420-426 : 421-423

Australotaenia hobbsi n. sp.

( Figs. 1–7 )

Type and only host. Ranoidea australis (Gray, 1842) ( Anura : Hylidae ).

Site of infection. Intestine.

Type and only locality. Adelaide River , Northern Territory, Australia, collected on December 23, 1978 by R. Hobbs .

Type material. Holotype (A44/ MU, one slide with whole-mounted specimens, nine slides with cross-sections).

Material studied. One slide with stained specimen and nine slides with cross sections (A44/ MU).

Etymology. The species is named in honour of Russell Hobbs from Murdoch University, Perth, Australia.

Morphological description (based on one complete specimen holotype from Ranoidea australis ; all measurements are given in micrometres unless otherwise stated; x = mean, n = number of measurements.): Proteocephalidae , Acanthotaeniinae. Total length 154 mm long, maximum width 1.75 mm wide, with proglottids up to 1.5 mm long. Strobila acraspedote, anapolytic. Immature, mature and pregravid wider than long (length/width ratio 0.34–0.67, 0.66–0.76, and 0.72–0.89, respectively; Figs. 2, 3 ); gravid proglottids wider than long to quadrate (length/width ratio 0.82–1.01; Fig. 4 ). Tegument thin, about 5 in thickness.

Scolex small, narrower than neck ( Fig. 1 ), aspinose, 565 long and 570 wide. Suckers uniloculate, spherical, directed laterally ( Fig. 1 ). Apical part of scolex dome-shaped, 355 long and 255 wide, containing large glandular apical organ, 125 long and 145 wide ( Fig. 1 ); retractor muscles not observed. Neck up to 665 wide; unsegmented zone posterior to scolex to first recognisable proglottids long (up to 6.5 mm).

Inner longitudinal musculature weakly developed, consisting of few bundles of muscular fibres ( Figs. 6, 7 ); they are few or missing laterally, making clear delimitation of medulla and cortex impossible. Osmoregulatory canals median to vitelline follicles ( Figs. 2, 3 ). Ventral canals thin-walled, almost indistinguishable ( Fig. 2 ); dorsal canals straight, thick-walled, about 5 in diameter, situated between vitelline follicles and testes, lateral to ovary ( Figs. 2, 3 ). Genital ducts run between osmoregulatory canals.

Testes spherical, 55–80 long and 55–75 wide, in one layer and in one field between vitelline follicles, more concentrated laterally and anteriorly ( Fig. 2 ); 69–92 (x = 83, n = 11) in number, overlapping dorsally vas deferens ( Fig. 2 ). Testes reach anterior margin of proglottids anteriorly and ovary posteriorly ( Figs. 2, 3 ). Vas deferens strongly coiled, never reaching mid-line of proglottid, occupying slightly elongated area ( Fig. 3 ). Cirrus-sac small, pear-shaped, thin-walled, 175–210 long by 85–95 wide ( Figs. 2 , 5 ); length: width ratio 1.53–2.20. Length of cirrus-sac represents 12–15% (x = 13%, n = 11) of proglottid width ( Figs. 2, 3 ). Cirrus occupies about 60% of length of cirrus-sac ( Fig. 5 ). Genital atrium narrow and deep ( Fig. 5 ); genital pore equatorial to slightly pre-equatorial, at 44–51% (x = 48%, n = 11) of proglottid length; genital pores irregularly alternating ( Figs. 2, 3 ).

Ovary large, deeply follicular, butterfly-shaped, 905–1095 wide ( Figs. 2, 3 ). Width of ovary represents 67–77% (x = 71%, n = 11) of proglottid width; length of ovary represents 30–44% of proglottid length ( Figs. 2, 3 ). Relative ovarian size, i.e., ratio of ovary surface of ovary to surface of proglottid (see de Chambrier et al. 2012) 17%. Vagina anterior or posterior to cirrus-sac, without vaginal sphincter, lined with thin layer of cells in its terminal (distal) part ( Fig. 5 ). Mehlis’ gland 70–110 in diameter, representing 5.2–7.8% of proglottid width ( Fig. 3 ).

Vitelline follicles spherical to oval, arranged in two lateral, longitudinal bands on lateral sides of proglottid, occupying 89–98% and 92–95% of length of proglottid on poral and aporal sides, respectively ( Figs. 2, 3 ); bands uninterrupted dorsally on poral side at level of terminal genitalia (cirrus-sac and vagina; Fig. 5 ). Follicles closely approaching, but not reaching, anterior or posterior margin of proglottids ( Figs. 2, 3 ). Most vitelline follicles situated in medulla, with a few follicles reaching to cortex, making them paramuscular ( Figs. 6, 7 ).

Primordium of uterine stem ventral ( Figs. 2 , 6 ). Formation of uterus of intermediate type described by de Chambrier et al. (2004, 2015). Gravid proglottids with 9–14 lateral diverticula ( Fig. 4 ). In terminal proglottids, uterine diverticula represent up to 76% of proglottid width ( Fig. 4 ). Eggs spherical, embryophore 19–22 in diameter, oncospheres 12–13 in diameter ( Figs. 8, 9 ).

Differential diagnosis. The present species is classified in Australotaenia based on the medullary position of the gonads, with the uterine stem in the cortex, the scolex with a glandular-muscular apical organ, the unilocular suckers, the internal longitudinal musculature consisting of a few isolated muscle fibre bundles, follicular ovary, testes forming two separated fields (except for very anterior testes in some species) and intermediate uterine development according to de Chambrier et al. (2015).

Australotaenia comprises three species, two of which have been described in hylid frogs ( Amphibia: Hylidae ), namely A. hylae ( Johnston, 1912) (syn. Ophiotaenia hylae Johnston, 1912 ) from southeastern Australia and A. grobeli of Litoria aurea from southwestern Australia and A. bunthangi , which parasitises the homalopsid snake, Enhydris enhydris (see Johnston 1912; de Chambrier 2004; de Chambrier & de Chambrier 2010; de Chambrier & Scholz 2012).

Australotaenia hobbsi n. sp. differs from the three other Australotaenia species by (i) the broader strobila (maximum body width 1,750 µm versus <930 µm), the scolex (570 µm versus less than 390 µm) and the suckers (215–230 µm in diameter versus less than 140 µm); (ii) the smaller relative size of the cirrus sac (12–15% of the proglottid width versus 17–33%) and (iii) the absence of a vaginal sphincter (present in the three other species). The new species also differs from A. grobeli and A. bunthangi in having a slightly higher number of testes (69–92 versus 46–76 and 46–64, respectively) (see Table 1 for the dimensions of each species).

Figures

FIGURES 1–4. Australotaenia hobbsi n. sp. from Ranoidea australis, Australia; holotype (A44/MU) 1―scolex; 2―mature proglottid, ventral view; ventral osmoregulatory canals indistinguishable except for the aporal pre-equatorial region; 3― pregravid proglottid, dorsal view; note the presence of numerous testes; 4―sketch of lateral uterine diverticula and the ovary in gravid proglottid, ventral view; note the posterior extension of the uterus situated ventral to the ovary and reaching to the posterior margin of the proglottid. Abbreviations: ao—apical organ; cc—chromophilic cells; cm—circular muscles; do—dorsal osmoregulatory canal; du— diverticula of uterus; gc—gland cells; Mg—Mehlis’ gland; ov—ovary; rm—retractor muscles; su—sucker; te—testes; ud— uteroduct; us—uterine stem; vi—vitelline follicles; vo—ventral osmoregulatory canals.

FIGURES 5–9. Australotaenia hobbsi n. sp. from Ranoidea australis, Australia; holotype (A44/MU). 5―terminal genitalia, dorsal view; note the absence of a vaginal sphincter. 6―cross section at the level of testes; note a weak inner longitudinal musculature represented by a few isolated muscle fibres. 7―cross section at the level of the ovary; note the presence of the uterus at level of ovarian isthmus. 8, 9―eggs. Abbreviations: cc—chromophilic cells; ci—cirrus; cs—cirrus sac; do—dorsal osmoregulatory canal; du—diverticula of uterus; em—embryophore; ga—genital atrium; lm—inner longitudinal musculature; Mg—Mehlis’ gland; oe—outer envelope; on— oncosphere; ov—ovary; sc—subtegumental cells (illustrated only partially on dorsal side); te—testes; tg—tegument; us— uterine stem; va—vas deferens; vc—vaginal canal; vi—vitelline follicles.