Australophiotaenia Chambrier & Beveridge & Scholz 2018, n. gen.

Australophiotaenia n. gen.

Diagnosis. Usually medium to large-sized worms (up to 400 mm long). Strobila acraspedote, mature and pregravid proglottids wider than long to longer than wide, gravid proglottids much longer than wide. Scolex wider than neck (proliferation zone), suckers uniloculate, usually large, directed anteriorly. Apical organ may be present. Testes medullary, in two well-separated lateral fields, in one, rarely two layers. Cirrus-sac pyriform, usually not reaching midline of proglottid. Vagina posterior or anterior to cirrus-sac, rarely only anterior. Vaginal sphincter often present. Genital pores irregularly alternating, post-equatorial to equatorial. Ovary medullary, small, with narrow lateral lobes. Vitelline follicles arranged in two dorsal and paramuscular lateral bands, not reaching anterior and posterior margins of proglottid. Formation of the uterus of type 1 (see de Chambrier et al. 2004, 2015). Eggs with a three-layered thick-walled embryophore, in clusters in some species. Parasites of Australian reptiles. Type species Australophiotaenia gallardi (Johnston, 1911) n. comb. (syns Proteocephalus gallardi Johnston, 1911; Ophiotaenia gallardi [Johnston, 1911])

Differential diagnosis. Species of Australophiotaenia n. gen. were previously placed in Ophiotaenia (see Freze 1965; Schmidt 1986) but they can be distinguished from those currently retained in this polyphyletic genus (see de Chambrier et al. 2015) by the possession of the following characteristics: a three-layered thick-walled embryophore, a scolex with large, anteriorly directed suckers, exclusively dorsal and paramuscular position of vitelline follicles (i.e., follicles may penetrate into the medulla between fibres of the inner longitudinal musculature) (de Chambrier 1990), and a postequatorial to equatorial genital pore in most species. Molecular data support the erection of the new genus because its four species for which DNA data are available form a strongly supported monophyletic clade (see Fig. 23 in Scholz et al. 2013). Furthermore, all species of the new genus occur in reptilian hosts (snakes and lizards) from the same zoogeographical region (Australasia).

Remarks. The genus Ophiotaenia was described by La Rue (1911) with O. perspicua La Rue, 1911 from the diamondback water snake, Nerodia rhombifer (Hallowell, 1852) (Colubridae: Natricinae) in Illinois, USA as its type species. Subsequently, more than 100 nominal taxa from reptiles and amphibians in temperate, subtropical and tropical zones worldwide have been assigned to this catch-all genus (Schmidt 1986; Ammann & de Chambrier 2008; de Chambrier et al. 2010; de Chambrier & Gil de Pertierra 2012; de Chambrier et al. 2017). However, molecular data have revealed this genus as polyphyletic and as many as 10 distinct genetic lineages of Ophiotaenia were found in the most comprehensive molecular phylogenetic analysis by de Chambrier et al. (2015).

Therefore, this artificial assemblage of taxa sharing somewhat similar morphology (a simple scolex with four spherical, uniloculate suckers; elongate proglottids, containing two well-separated longitudinal testis fields; medullary testes, ovary, uterus and in most cases vitelline follicles) is in urgent need of taxonomic revision (Scholz et al. 2013; de Chambrier et al. 2017). Ophiotaenia has to be split into several (at least 10 as indicated by de Chambrier et al. 2015) distinct genera to retain monophyly of the genera. However, species of these putative new genera often share a similar morphology and it is difficult or even impossible to find morphological characteristics that would provide straightforward circumscription of individual genera. As a result, distinguishing combinations of non-unique morphological characteristics need to be searched for to adequately define genetically distinct lineages of previously congeneric taxa. Biological (host associations) and zoogeographical (distribution) traits may also help in this effort to build up a new, more natural classification of proteocephalid tapeworms from reptiles and amphibians (but also from their dominant definitive hosts, i.e. freshwater bony fishes). A similar situation exists in numerous animal groups including other fish parasites, myxozoans (see Fiala et al. 2014), in which shape of spores represent a highly homoplastic character, whereas environment (marine or freshwater) and site of infection (histozoic or coelozoic) better reflect the evolutionary history of the group.