Ithyoclinostomum yamagutii n. sp. (Digenea: Clinostomidae) in the great blue heron Ardea herodias L. (Aves: Ardeidae) from Mississippi, USA

Size does not matter: molecular phylogeny reveals one of the largest trematodes from vertebrates, the enigmatic Ithyoclinostomum dimorphum, as a species of Clinostomum (Trematoda: Clinostomidae)

“…In our phylogenetic analyses, the recently described Ithyoclinostomum yamagutii presented as an early diverging and isolated lineage from other clinostomids, as previously shown by Briosio-Aguilar et al (2019) and Rosser et al (2020) . On one hand, these authors assigned their specimens to Ithyoclinostomum primarily based on: the large body size, the position of the cirrus-sac (pre-testicular), the testes shape (deeply lobed), the position of gonads in the posterior fourth of the body, and the large free area (void of any internal organ) between the ventral sucker and anterior testis; these features are found in the type species of the genus, Ithyoclinostomum dimorphum, now C. dimorphum .…”

“…brieni further differs from the 'typical' Clinostomum species by having the genital pore post-testicular and the whole genital complex extremely close to the posterior end. These findings depict an opposing scenario to recent molecular phylogenetic studies ( Woodyard et al, 2017 ; Rosser et al, 2020 ) that have endorsed previous morphological arrangement for the family (Kanev et al, 2002). Moreover, our data raise doubts concerning which morphological features are informative at higher-level classification schemes.…”

“…The models used were as follows: TVM+F+G4 for both ITS-1 and ITS2, and K2P+I for 5.8S, all included in the ribosomal gene cluster ITS1-5.8S-ITS2 alignment (3 partitions); TVM+F+I+G4 for the 28S dataset alone; TIM3+F+I+G4, TIM+F+G4, GTR+F+G4, for the 1st, 2nd and 3rd codon positions of the cox 1 dataset, respectively (3 partitions); GTR+F+G4, K2P+I, TVM+F+G4, TVM+F+I+G4, TN+F+G4, K3Pu+F+G4, TPM2+F+G4, for the ITS1, 5.8S, ITS2, 28S, cox 1 1st + 2nd + 3rd codon positions of the concatenated dataset (7 partitions). Outgroups were chosen based on previous phylogenetic studies ( Briosio-Aguilar et al, 2019 ; Rosser et al, 2020 ; Montes et al, 2021 ).…”

“…More than 30 species have been described worldwide, resulting in a complex taxonomy revised by different authors over time ( Braun, 1901 ; Ukoli, 1966 ; Kanev et al, 2002 ). The use of molecular data has allowed important advances in the knowledge of this group, including the description of new species, the link between larval stages and adults and inferences about the phylogeny, ecology and biogeography of clinostomids (e.g., Caffara et al, 2011 , 2019 ; Locke et al, 2015 , 2019 ; Woodyard et al, 2017 ; Rosser et al, 2017 , 2020 ; Sereno-Uribe et al, 2018 ). However, a proper classification that reflects the evolutionary history of the group is still in progress and far from being achieved, mainly because molecular data for some key taxa (type genera and species) is lacking.…”

“…Despite advances in the phylogenetic classification of trematodes, especially Clinostomidae, there are still no sequences available to I. dimorphum , the type species of the genus Ithyoclinostomum . More recently, the second species of the genus, Ithyoclinostomum yamagutii Rosser et al, 2020, was described from birds and linked to metacercariae from fish in North and Middle America ( Briosio-Aguilar et al, 2019 ; Rosser et al, 2020 ). Again, the large size (∼25 mm; yet much smaller than I .…”