<i>Macrobothriotaenia ficta</i> (Cestoda: Proteocephalidea), a parasite of sunbeam snake (<i>Xenopeltis unicolor</i>): example of convergent evolution

Abstract

The poorly known proteocephalidean cestode Macrobothriotaenia ficta (Meggitt, 1931) from the sunbeam snake Xenopeltis unicolor (Ophidia: Xenopeltidae) is redescribed on the basis of re-examination of its type specimens from Burma (Myanmar), and vouchers from Thailand and Vietnam. The peculiar morphology of the scolex, which is formed by four pedunculate lobe-bearing pincer-shaped suckers, is described for the first time using scanning electron microscopy. In scolex morphology, M. ficta closely resembles phyllobothriidean cestodes, parasites of elasmobranchs. However, this similarity does not reflect phylogenetic relatedness of these cestodes but instead presents an example of convergent morphological evolution of attachment organs of unrelated groups of cestodes that parasitize different groups of vertebrates. Besides scolex morphology, the genus is characterised by the possession of a very large cirrus-sac, which may reach up to the midline of proglottides, few testes (less than 60), vitelline follicles limited to the dorsal side of proglottides, a large vaginal sphincter, and eggs with a three-layered embryophore covered with rounded projections. Numerous errors in the diagnosis of M. ficta, which appeared in the literature as a result of uncritical compilation of data without examination of original material, are corrected. Multilocus phylogenetic analysis of nuclear ribosomal RNA genes ssr-and lsrDNA and mitochondrial genes rrnL and cox1 place this species among other snake-parasitizing proteocephalideans of the genus Ophiotaenia. The convergent evolution of scolex morphology across distantly related taxa is discussed.

A large 28S rDNA-based phylogeny confirms the limitations of established morphological characters for classification of proteocephalidean tapeworms (Platyhelminthes, Cestoda)

“…the Proteocephalus aggregate (Scholz et al 2007); African Proteocephalus (de Chambrier et al 2011); Testudotaenia Freze, 1965 (de Chambrier et al 2009a), Corallobothriinae (Rosas-Valdez et al 2004, Scholz et al 2011)] or employed only a very limited taxon sampling (e.g. Zehnder and de Chambrier 2000, Škeříková et al 2001, de Chambrier et al 2008, Scholz et al 2013). …”

A new genus of proteocephalid tapeworm (Cestoda) from the marbled swamp eel Synbranchus marmoratus Bloch (Synbranchiformes: Synbranchidae) in the River Parana basin, Argentina

“…Homoplasy of morphological characteristics, especially those of the scolex, has been observed in several groups of proteocephalideans [e.g. Scholz et al 2013-Macrobothriotaenia ficta (Meggitt, 1931]. In South America, there are two other proteocephalidean genera from fishes that do not possess a metascolex and that bear four biloculate suckers in the scolex, similar to the members of the three above-mentioned monticelliine genera, i.e.…”

A new species of Pseudocrepidobothrium (Cestoda: Proteocephalidea) from Pseudoplatystoma reticulatum (Pisces: Siluriformes) in the Paraná River basin (Argentina)

“…On the other hand, the scolex can also be shared by genera belonging to different subfamilies, as for example Harriscolex and Houssayela with Euzetiella de Chambrier, Rego et Vaucher, 1999 of the Proteocephalinae, and these three with Regoella Arredondo, de Chambrier et Gil de Pertierra, 2013 of the Monticelliinae (de Chambrier et al 1999, de Chambrier and Scholz 2005, Gil de Pertierra and de Chambrier 2013, Arredondo et al 2013. Likewise, Macrobothriotaenia Freze, 1965 and Thaumasioscolex Cañeda-Guzmán, de Chambrier et Scholz, 2001 (both Proteocephaliinae) show a similar scolex morphology (formed by four lobes, with each lobe containing an unilocular, pincer-shaped sucker), but in fact they are not closely related species as demonstrated by Scholz et al (2013); the similarity in the morphology of both scoleces has been explained as an adaptation to the morphology of the hosts' intestine (Scholz et al 2013). In the case of the other above-mentioned genera, it will be interesting to clarify whether the similar shape of the scolex is an evidence of relationship or represents a homoplastic character as a result of convergent evolution.…”