A new species of Angiostoma (Angiostomatidae) is described from the intestine of the plethodontid salamander, Pseudoeurycea mixteca from Puebla State, in central Mexico. The new species closely resembles Angiostoma limancis, Angiostoma kimmeriensis, Angiostoma spiridonovi, Angiostoma stammeri, and Angiostoma carettae, because they all possess 8 pairs of pedunculate papillae in the caudal region; however, the new species can be distinguished by the unique arrangement of papillae, with 1 pre-cloacal pair, and 7 post-cloacal pairs. Among the 12 congeneric species of Angiostoma described so far, 2 have been described as parasites of salamanders, Angiostoma plethodontis from Plethodon cinereus and Plethodon richmondi in Virginia, USA, and Angiostoma onychodactyla from Onychodactylus japonicus in Japan. Angiostoma lamotheargumedoi n. sp. is readily distinguished from these 2 species by the presence of lateral alae and by the number of pre-cloacal papillae.

A new species and genus of Acanthocephala is described based on specimens found in the intestine of Anisotremus interruptus (Gill, 1862), Haemulon sexfasciatum Gill, 1863, Haemulon scudderi Gill, 1863, Pomadasys leuciscus (Günther, 1864), and Eugerres sp. Jordan and Evermann, 1927, from the marine waters of Chamela Bay, Jalisco, México. Koronacantha mexicana n. sp. is characterized by having an elongate proboscis with a heavy cuticle, cuticular body spines, and 8 cement glands, indicating that it should be assigned to the Illiosentidae Golvan, 1960. The genus Koronacantha n. gen. can be distinguished from other members of the family by the possession of (1) a row of heavy, strongly recurved proboscis hooks in the shape of an inverted apostrophe with roots that are simple but exaggerated in size and a small hook blade, occurring just anterior to a posteriormost comblike group of 4 or 5 small, close-set hooks, (2) cerebral ganglion near middle of proboscis receptacle, and (3) paired sensory papillae at mid-neck.

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Morphologically similar species, that is cryptic species, may be similar or quasi-similar owing to the deceleration of morphological evolution and stasis. While the factors underlying the deceleration of morphological evolution or stasis in cryptic species remain unknown, decades of research in the field of paleontology on punctuated equilibrium have originated clear hypotheses. Species are expected to remain morphologically identical in scenarios of shared genetic variation, such as hybridization and incomplete lineage sorting, or in scenarios where bottlenecks reduce genetic variation and constrain the evolution of morphology. Here, focusing on three morphologically similar Stygocapitella species, we employ a whole-genome amplification method (WGA) coupled with doubledigestion restriction-site associated DNA sequencing (ddRAD) to reconstruct the evolutionary history of the species complex. We explore population structure, use population-level statistics to determine the degree of connectivity between populations and species, and determine the most likely demographic scenarios which generally reject for recent hybridization. We find that the combination of WGA and ddRAD allowed us to obtain genomic-level data from microscopic eukaryotes (~1 millimetre) opening up opportunities for those working with population genomics and phylogenomics in such taxa. The three species share genetic variance, likely from incomplete lineage sorting and ancient admixture. We speculate that the degree of shared variation might underlie