Morphological and molecular description of Corynosoma paraevae n. sp. (Acanthocephala: Polymorphidae) juveniles from Notothenia coriiceps Richardson (Perciformes: Nototheniidae) in Argentine Islands, West Antarctica.

Abstract

Adults of Corynosoma evae Zdzitowiecki, 1984 were described from the leopard seal Hydrurga leptonyx (Blainville) in South Shetlands, South Georgia, and Falkland Islands and juveniles from the Antarctic dragonfish Parachaenichthys georgianus (Fischer) were also reported. We describe excysted juveniles of a morphologically indistinguishable cryptic species, Corynosoma paraevae n. sp. from the body cavity of Notothenia coriiceps Richardson collected off Galindez Island, Argentine Islands, West Antarctica. Our juveniles were generally smaller than those of adults of C. evae but most other measurements were comparable. We compared our morphometric description of C. paraevae n. sp. juveniles from N. coriiceps with the one available for C. evae adults collected from H. leptonyx and the juveniles redescribed from three other species of Antarctic notothenioid fish. We have included optical microscopy and scanning electron microscope (SEM) images of internal and external structures, respectively. Various cuts of proboscis hooks and roots studied by Energy Dispersive X-ray analysis (EDXA) revealed the highest levels of calcium, phosphorous, and sulfur reaching 50.55%, 20.30%, and 4.15%, respectively. This pattern is compared with those of cystacanths of 6 other species of acanthocephalans. Our molecular description of the new cryptic species involved the 18S subunit of ribosomal DNA and mitochondrial cytochrome c oxidase subunit 1 (cox1) from mitochondrial DNA. The cox1 tree showed that the four isolates of the new species and two of C. evae from the same collection form separate clades that confirmed C. paraevae n. sp. as different species. The cox1 interspecific relationship inferred with 14 sequences revealed 08 groupings alienated from each other.