Heterorchis, Baylis, 1915

Curran, Stephen S., Dutton, Haley R., Warren, Micah B., Preez, Louis du & Bullard, Stephen A., 2021, Two new species of Cephalogonimidae Looss, 1899 (Digenea: Plagiorchioidea) from Africa (Mozambique and Guinea), including a new phylogenetic hypothesis for related plagiorchioids, International Journal for Parasitology: Parasites and Wildlife 14, pp. 228-240 : 238-239

4.2. Systematics of Heterorchis

No information is available related to the cercariae for species from Heterorchis , and the excretory system exhibited in adult worms is so unusual that the position of Heterorchis among the flukes has been debated since the genus was erected. Baylis (1915) tentatively classified the genus in the Plagiorchiidae based on a general collection of features that conform to species in the plagiorchioid group: a scaled tegument, configuration of the alimentary tract, Y-shaped excretory bladder, small operculated tanned eggs, and a marginal anterior genital pore on the left side. Subsequent workers have either tentatively agreed with Baylis ( Dollfus, 1950; Prudhoe and Bray, 1982; Bray, 1988) or classified the genus in the Fellodistomatidae ( Yamaguti, 1953, 1958, 1971; Thomas, 1958b; Fischthal and Thomas, 1968; Vassiliad`es and Richard, 1970; Boeger and Thatcher, 1983). The modern concept of the Fellodistomatidae entails a marine life history and the absence of a designated seminal receptacle (see Bray, 2002), both of which are violated by Heterorchis spp. , which are entirely freshwater, and all have a prominent seminal receptacle. A fluke ( Kalipharynx piramboae Boeger & Thatcher, 1983 ) discovered infecting South American lungfish, Lepidosiren paradoxa Fitzinger ( Lepidosirenidae ) from the Amazon region of Brazil may represent the closest relative to Heterorchis ( Boeger and Thatcher, 1983) . Kalipharynx piramboae is a monotypic species, and like Heterorchis , Kalipharynx Boeger & Thatcher, 1983 is presently considered incertae sedis in the Plagiorchioidea (Tkach in Pojmanska´et al., 2008). While the excretory system of K. piramboae is incompletely described, it does have a terminal excretory pore rather than a large dorsal one, but otherwise, overall morphology is very similar between species in the two genera. Both groups share scale-like spines covering the body, robust suckers, a submarginal genital pore, extensive uterus with small operculated eggs, and the ovarian complex is nearly identical in both forms. We collected a single adult individual of K. piramboae from the intestine of L. paradoxa from Iquitos, Peru, and the excretory system of the specimen is largely obscured by the gonads and extensive coils of the uterus. However, convoluted lateral excretory collecting ducts are visible in the anterior half of the worm, suggesting the bladder may be Y-shaped. Metacercariae belonging in Kalipharynx were reported in two species of planorbid snails in Argentina ( Biomphalaria tenagophila [D’ Orbigny] and Biomphalaria occidentalis Paraense ), but the excretory system was not further described in the specimens (Virginia-Fern´andez et al., 2013). Closer study of the museum specimens from that study may provide insight into the condition of the excretory bladder. The addition of more detailed study of the larval stages of K. piramboae and appropriation of nucleotide data from that species may provide great insight into the

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relationship between Kalipharynx and Heterorchis , and ultimately their position and family status within the Plagiorchioidea .