Elemental Composition of Proboscis Hooks in Metacanthocephalus rennicki inflatus (Acanthocephala: Rhadinorhynchidae) from Antarctic Notothenia coriiceps
Résumé
Aims: Specimens of Metacanthocephalus (Bimuscularis) rennicki inflatus (Amin et al., 2025) (Acanthocephala: Rhadinorhynchidae) from Notothenia coriiceps Richardson collected off Galindez Island, West Antarctica were studied for metal analysis of hooks. We report on the Energy Dispersive X-ray Analysis (EDXA) for this acanthocephalan or any member of the same genus for the first time. History: We have described the mineral distribution in the margins and center of the anterior, middle, and posterior proboscis hooks of cystacanths of many acanthocephaln species. Our studies included X-ray scans (EDXA) of FIB-sectioned hooks and spines of these acanthocephalan worms. The chemical composition of the hooks is characteristic of acanthocephalans. Study Design: We report here a new aspect of elemental analysis of hooks demonstrating the differential distribution of sulfur, phosphorous, calcium, and magnesium at the tip, middle, and base of anterior, middle and posterior hooks. SEM data maps were created, marking spectra from the edge and middle of hook tips, middle, and roots. These were followed by color-coded spectra showing magnesium, calcium, phosphorous, and sulfur element overlays. Then, graphs and tables were created for each spectrum of anterior, middle, and posterior hooks. Place and Duration of Study: The study took over one year between collecting data in Antarctica, processing specimens in Ukraine and the United States and laboratory work in Brazil. Methodology: The fixed samples were dehydrated through a graded ethanol series and subsequently were critical point dried using a Tousimis Autosamdri-815 (Tousimis Research Corporation, Rockville, MD, USA). Samples were mounted on aluminum stubs and coated with a 20 nm layer of carbon using a Balzers MED 010 sputter coater (Balzers Union Ltd., Balzers, Liechtenstein). Results and conclusions: We demonstrated highest levels of calcium in all hooks especially middle hook tips (56.0%) compared to somewhat lower levels of phosphorus also in all hooks. The lowest level of both these two elements was found in the base of anterior hooks (15% and 9.2%). Sulfur and magnesium were also found in all hooks but at negligible levels. Calcium was found to be the most prevalent element in the middle hooks. Phosphorous was highest in the tip of posterior hooks (23.7%). Sulfur was most negligible (0.3%) in anterior hook tip but most pronounced (1.1%) in anterior hook base and middle of posterior hook. Magnesium was somewhat more prevalent reaching 2.9% at the anterior hook tip. Importance: The biological importance of this pattern is discussed in terms relevance to hook strength and flexibility, species identity and comparative systematics. This EDXA profile of Metacanthocephalus (Bimuscularis) rennicki inflatus was distinctly differentiated from that of morphologically related species especially those that co-infected the same host species.