New Morphological and Molecular Data on Lobatostoma anisotremum Oliva & Carvajal, 1984 (Trematoda: Aspidogastridae) from Anisotremus scapularis (Tschudi, 1846) (Eupercaria incertae sedis: Haemulidae) off the Peruvian Coast, with Insights into the

The aspidogastrean genus Lobatostoma Eckmann, 1932 remains poorly understood, with limited morphological and molecular data hindering its systematics and phylogenetic resolution. In the present study, we provide the first integrative characterisation of Lobatostoma anisotremum Oliva & Carvajal, 1984 from the southeastern Pacific coast of Peru, combining detailed morphological, ultrastructural and molecular analyses. A total of 137 specimens were recovered from the intestine of 65 Peruvian grunt, Anisotremus scapularis (Tschudi, 1846) (Haemulidae), with a prevalence of 43% and mean abundance of 2.1 ± 3.4 parasites per host. Morphological observations based on light microscopy and scanning electron microscopy (SEM) allowed the refinement of diagnostic features, including tegumental papillae distribution, marginal organs, and reproductive structures. Molecular characterisation included the generation of novel sequences for the 18S rDNA and 28S rDNA gene fragments, representing the first comprehensive molecular dataset for L. anisotremum. Phylogenetic analyses based on 18S and 28S rDNA datasets consistently recovered L. anisotremum as sister to L. manteri Rohde, 1973, with strong support in the 28S analysis. In contrast, L. kemostoma (MacCallum & MacCallum, 1913) was recovered as a distinct and independent lineage, clearly separated from other congeners, supporting previous hypotheses of non-monophyly within Lobatostoma. These findings could be further supported by consistent morphological differences, particularly in cephalic lobe configuration, hindbody length and number of alveoli on the ventral disc. Our results also suggest that current family- and subfamily level classifications within Aspidogastridae Looss, 1901 may not reflect evolutionary relationships, as evidenced by the nested position of Multicalycidae Gibson & Chinabut, 1984 and the apparent non-monophyly of traditionally defined subfamilies. Although our data supports the distinctiveness of certain lineages, including L. kemostoma, we refrain from proposing formal taxonomic changes due to limited taxon sampling and the need for a comprehensive revision of the group. Overall, this study highlights the importance of integrative approaches in resolving the systematics of Aspidogastrea Faust & Tang, 1936 and provides a robust framework for future taxonomic and phylogenetic studies.