A paradigm for the recognition of cryptic trematode species in tropical Indo-west Pacific fishes: the problematic genus Preptetos (Trematoda: Lepocreadiidae)

Three new species of Helicometroides Yamaguti, 1934 from Japan and Australia, with new molecular evidence of a widespread species

“…The interpretation of genetic variation in marine fish trematodes for the recognition of species is receiving substantial attention, particularly in the light of ITS2 and cox 1 sequence data (Bray et al ., 2021). Recent studies in the tropical Indo-west Pacific using the cox 1 region have frequently identified morphologically indistinguishable trematodes in the same or comparable fishes forming distinct clades based on the geographical distribution (allopatric populations) as reflecting intraspecific variation rather than distinct species.…”

“…Recent studies in the tropical Indo-west Pacific using the cox 1 region have frequently identified morphologically indistinguishable trematodes in the same or comparable fishes forming distinct clades based on the geographical distribution (allopatric populations) as reflecting intraspecific variation rather than distinct species. Such findings have been reported for six species of the Aporocotylidae Odhner, 1912 (Cutmore et al ., 2021), three species of the Gorgocephalidae Manter, 1966 (Huston et al ., 2021), three species of the Lepocreadiidae Odhner, 1905 (Bray et al ., 2018, 2021) and seven species of the Monorchiidae Odhner, 1911 (McNamara et al ., 2014; Wee et al ., 2021 a ). These intraspecific variations are much reduced in the ITS2 region (in some cases, the differences in the ITS2 region disappear entirely), resulting in the interpretation of a single population (one clade) rather than multiple populations (distinct clades).…”

“…These intraspecific variations are much reduced in the ITS2 region (in some cases, the differences in the ITS2 region disappear entirely), resulting in the interpretation of a single population (one clade) rather than multiple populations (distinct clades). For example, Preptetos paracaballeroi Bray et al ., 2021 occurs at Heron and Lizard Islands where the populations differ by 27–31 base pairs in the cox 1 region while there are no differences at all for the ITS2 region. Such dramatic conflict in genetic variation between cox 1 and ITS2 sequences has presented a significant obstacle in the interpretation of the status of some populations.…”

“…However, the nature of the H. longicollis complex presents components not accounted for by the criteria proposed by Bray et al . (2021). Specifically in this system, cryptic morphology is paired with sympatric lineages identified from a recombinant region (ITS2) in addition to a non-recombining region ( cox 1).…”

A new order of fishes as hosts of blood flukes (Aporocotylidae); description of a new genus and three new species infecting squirrelfishes (Holocentriformes, Holocentridae) on the Great Barrier Reef

“…Some individual worms were processed for both morphological and molecular analysis (hologenophores, sensu Pleijel et al [ 48 ]). Species were delineated using an integrative interpretation of morphological, ecological, and genetic data, following the criteria of trematode species recognition proposed by Bray et al [ 6 ] (i.e. reciprocal monophyly in the most discriminating available molecular marker + distinction in morphology or host distribution).…”