First report of hexabothriid monogeneans from Australian carcharhinids

Area of Science:

• Parasitology
• Marine Biology
• Molecular Phylogenetics

Background:

• Hexabothriidae are monogenean parasites infecting elasmobranchs.
• Previous records of Heteronchocotyle leucas and Erpocotyle carcharhini are limited.
• The hexabothriid fauna of Australian carcharhinids was previously undocumented.

Purpose of the Study:

• To describe new host and geographic records for H. leucas and E. carcharhini in Australia.
• To investigate potential host-specific adaptations in H. leucas morphology.
• To provide molecular data and explore phylogenetic relationships of these hexabothriids.

Main Methods:

• Morphological analysis of collected parasites.
• Morphometric measurements and statistical correlation with host size.
• DNA extraction and sequencing of the 28S ribosomal RNA gene.

Main Results:

• First report of H. leucas and E. carcharhini from Australian carcharhinids, establishing new host records.
• H. leucas populations showed significant size variation across different host species, suggesting adaptation.
• Sucker sclerite size in H. leucas correlated positively with worm growth, maintaining functional shape; early-developing sclerites became redundant.
• Novel 28S rRNA sequences for H. leucas and E. carcharhini were generated, aiding phylogenetic placement within Hexabothriidae.

Conclusions:

• H. leucas and E. carcharhini are newly recorded in Australia, expanding their known distribution.
• Parasite size plasticity in H. leucas indicates adaptation to host-specific gill microhabitats.
• Sclerite development in H. leucas suggests a conserved growth pattern with early functionalization of key structures.