Taxonomy of Echinostoma revolutum and 37-Collar-Spined Echinostoma spp.: A Historical Review

Abstract

Echinostoma flukes armed with 37 collar spines on their head collar are called as 37-collar-spined Echinostoma spp. (group) or ‘Echinostoma revolutum group’. At least 56 nominal species have been described in this group. However, many of them were morphologically close to and difficult to distinguish from the other, thus synonymized with the others. However, some of the synonymies were disagreed by other researchers, and taxonomic debates have been continued. Fortunately, recent development of molecular techniques, in particular, sequencing of the mitochondrial (nad1 and cox1) and nuclear genes (ITS region; ITS1-5.8S-ITS2), has enabled us to obtain highly useful data on phylogenetic relationships of these 37-collar-spined Echinostoma spp. Thus, 16 different species are currently acknowledged to be valid worldwide, which include E. revolutum, E. bolschewense, E. caproni, E. cinetorchis, E. deserticum, E. lindoense, E. luisreyi, E. mekongi, E. miyagawai, E. nasincovae, E. novaezealandense, E. paraensei, E. paraulum, E. robustum, E. trivolvis, and Echinostoma sp. IG of Georgieva et al., 2013. The validity of the other 10 species is retained until further evaluation, including molecular analyses; E. acuticauda, E. barbosai, E. chloephagae, E. echinatum, E. jurini, E. nudicaudatum, E. parvocirrus, E. pinnicaudatum, E. ralli, and E. rodriguesi. In this review, the history of discovery and taxonomic debates on these 26 valid or validity-retained species are briefly reviewed.

Echinostoma mekongi: Discovery of Its Metacercarial Stage in Snails, Filopaludina martensi cambodjensis, in Pursat Province, Cambodia

“…The metacercariae of E. mekongi were almost round (163–190 μm in diameter), equipped with 37 collar spines on the head collar, and morphologically indistinguishable from those of the other 37-collar-spined Echinostoma spp. However, they were slightly or markedly larger than the metacercariae of E. lindoense (120–130 μm), E. revolutum (132–152 μm), E. miyagawai (144–154 μm), and E. trivolvis (135–170 μm) [ 1 ].…”

“…However, many of the other 37-collar-spined Echinostoma spp. are known to infect both birds and mammals, for example, E. revolutum , E. miyagawai , and E. trivolvis [ 1 ]. Although natural reservoir hosts for E. mekongi have never been discovered, this may also be applied to E. mekongi for taking both type of hosts.…”

“…or ‘ Echinostoma revolutum group’, total 26 valid or validity-retained spp. were acknowledged worldwide [ 1 ]. They included 16 valid species, i.e., E. revolutum , E. bolschewense , E. caproni , E. cinetorchis , E. deserticum , E. lindoense , E. luisreyi , E. mekongi , E. miyagawai , E. nasincovae , E. novaezealandense , E. paraensei , E. paraulum , E. robustum , E. trivolvis , and Echinostoma sp.…”

“…They included 16 valid species, i.e., E. revolutum , E. bolschewense , E. caproni , E. cinetorchis , E. deserticum , E. lindoense , E. luisreyi , E. mekongi , E. miyagawai , E. nasincovae , E. novaezealandense , E. paraensei , E. paraulum , E. robustum , E. trivolvis , and Echinostoma sp. IG of Georgieva et al, 2013, and 10 validity-retained species., i.e., E. acuticauda , E. barbosai , E. chloephagae , E. echinatum , E. jurini , E. nudicaudatum , E. parvocirrus , E. pinnicaudatum , E. ralli , and E. rodriguesi [ 1 ]. Recently, however, E. robustum Yamaguti, 1935 has been put to a synonymy with E. miyagawai Ishii, 1932 [ 2 ].…”

“…Recently, however, E. robustum Yamaguti, 1935 has been put to a synonymy with E. miyagawai Ishii, 1932 [ 2 ]. Eight among the 26 species, including E. revolutum , E. cinetorchis , E. echinatum , E. lindoense , E. mekongi , E. miyagawai (experimental infection), E. paraulum , and possibly E. paraensei (from the coprolite of a human mummy), are regarded as human-infecting 37-collar-spined echinostomes [ 1 ].…”