New perspectives of Microsentis wardae Martin & Multani, 1966 (Acanthocephala: Neoechinorhynchidae) from Gillichthys mirabilis Cooper in California, with scanning electron microscopy images and energy dispersive X-ray analysis

Fully developed, sexually mature small male and female acanthocephalans, Microsentis wardae Martin & Multani, 1966 (Neoechinorhynchidae) reaching only 2.25 mm and 2.42 mm, respectively, were collected from the rectum of longjaw mudsuckers, Gillichthys mirabilis Cooper, in the salty marches of Anaheim Bay and San Diego Bay, California. Our specimens were half the size of those reported in the original description from the same host in Scammon's Lagoon over 700 km to the south. The ratio of proboscis and receptacle size to trunk size was markedly higher in our specimens compared to the larger specimens measured in the original description. The anatomy of all structures in our specimens from Anaheim Bay was comparable to that of the larger Scammon's Lagoon specimens that have apparently realized more growth in the Scammon's Lagoon. We have observed more structures that are not reported in the original description, especially evident from our scanning electron microscopy images, which are not possible to observe in the original line drawings. In our specimens, the micropores were unusually widely spaced and the energy dispersive X-ray analysis showed longitudinal hook sections with high levels of sulphur and phosphorus and moderate levels of calcium, but the whole hooks showed highest levels of sodium and magnesium – the biochemical hook signature of this species. Sequences of the small subunit (18S) of the nuclear ribosomal DNA were generated and compared with acanthocephalan sequences available from GenBank. As M. wardae comprises a monotypic genus, therefore, phylogenetic analyses inferred from the 18S gene showed its relationship with other species of closely related genera of Eoacanthocephala. This is the first report of molecular data of M. wardae.