# Differential distribution of minerals in the proboscis hooks of Corynosoma pseudohamanni Zdzitowiecki, 1984 (Acanthocephala: Polymorphidae) juveniles from Notothenia coriiceps Richardson off Argentine Islands, West Antarctica

## TL;DR

This study examines the mineral composition of hooks in a specific parasitic worm found in Antarctic fish, revealing differences in elemental distribution that may aid in species identification.

## Contribution

The paper introduces the first elemental analysis of proboscis hooks in Corynosoma pseudohamanni juveniles using EDXA, revealing differential mineral distribution.

## Key findings

- Calcium was most prevalent in hook roots and centers, while sulfur was highest at hook tips.
- Phosphorus levels were consistent but lower than calcium, with sulfur negligible in roots.
- The elemental distribution pattern is proposed to have taxonomic and biological significance.

## Abstract

Corynosoma pseudohamanni Zdzitowiecki, 1984 (Polymorphidae) was described from the intestinal tract of 5 species of seals, including the type and primary host, the Weddell seal Leptonycotes weddellii (Lesson) in the South Shetlands, West Antarctica. Notothenia coriiceps Richardson was the primary paratenic host of 14 fish hosts reported in the original description. We redescribed excysted juveniles from the body cavity of N. coriiceps collected off Galindez Island, Argentine Islands, and included its molecular analysis, SEM images, and Energy Dispersive X-ray Analysis (EDXA) for the first time. The identity and distribution of mineral elements in the center and edge of anterior, middle, and posterior proboscis hooks establish their taxonomic relevance. Samples were dehydrated through an ascending ethanol series and then critical point dried, mounted on stubs and coated with carbon with a thickness of 20 nm. The specimens were examined and positioned using the LYRA3 FIB-SEM (TESCAN, Brno – Kohoutovice, Czech Republic), equipped with a Phoenix energy-dispersive X-ray analyzer (Oxford Instruments, Abingdon, England). X-ray spot and live scan analyses were performed at 15 kV with a spot size 2. The AZtec version 4.3 software system (Oxford Instruments, Abingdon, England) was used. We demonstrated the highest calcium levels in all hooks and hook roots compared to sulfur and phosphorus. Here, for the first time, we report a new aspect of the elemental analysis of hooks, demonstrating the differential distribution of sulfur, phosphorous, calcium, and magnesium at the center and margins of anterior, middle, and posterior hooks and hook roots. Calcium was the most prevalent element in roots (root edge and root middle) and the center of middle of all hooks. Phosphorous was equally common but not as prevalent and was highest in the middle of the roots and the middle of all hooks. Sulfur was negligible or absent in the roots and middle of all hooks but highest at hook tips and the edge of the middle hook. The biological and taxonomic importance of this EDXA pattern is discussed, as well as its relevance to hook strength and flexibility, species identity, and comparative systematics. Comparative results were also presented for cystacanths of five other species of acanthocephalans for which EDXA patterns have been studied.