elSSN : 2234-8190
elSSN : 2234-8190
elSSN : 2234-8190
First Records of Two Benthic Chaetognaths, Spadella japonica and Paraspadella gotoi (Chaetognatha), in the Coast of South Korea, with Taxonomic Reassessment Using Morphological and Molecular Data
Seohwi Choo1, Yvan Perez2, Man-Ki Jeong3, Ho Young Soh1,4,*
1Big Data Fishery Resource Management Interdisciplinary Program, Chonnam National University, Yeosu 59626, Korea
2Mediterranean Institute of Marine and Terrestrial Biodiversity and Ecology (IMBE) UMR 7263, Aix-Marseille University, University of Avignon, CNRS, Marseille, IRD, France
3Department of Smart Fisheries Resources Management, Chonnam National University, Yeosu 59626, Korea
4Department of Ocean Integrated Science, Chonnam National University, Yeosu 59626, Korea
The phylum Chaetognatha includes the Spadellidae, characterized by exclusive benthic species. Over the recent decades, 10 species belonging to Spadellidae have been discovered, each with unique habitats worldwide, including sediments, marine caves, and hydrothermal vent sites, underscoring the fragmented and isolated spatial distribution of Spadellidae species. Here, we report the first presence of Spadella japonica and Paraspadella gotoi in South Korean waters, two species previously described from specimens collected in South Japan. Comparative morphological analysis identified several variations from the former descriptions of S. japonica, mainly a larger adult size, a higher number of grasping spines, and the presence of posterior teeth. We also provide new scanning electron microscopy observations of P. gotoi which especialy focuses on the morphology of the adhesive organs. Molecular analyses using new sequences of small subunit ribosomal RNA genes enable to reassess the relationships of Spadellidae within Phragmophora with the broadest taxonomic sampling to date. We also generated cytochrome c oxidase subunit I mitochondrial (mtCOI) barcodes and all species always formed monophyletic groups in the phylogenetic analyses. Additionally, we observed highly divergent mitochondrial lineages in an interbreeding population of S. japonica. The intra- and interspecific genetic distances of mtCOI sequences within the genus Spadella reveals that the divergence between distinct lineages within a species is nearly as significant as that observed between different species. While considering the limitations of the mtCOI gene in establishing an accurate genetic threshold for species delimitation due to the absence of marked barcode gap, it remains an effective molecular marker for identifying congeneric chaetognath species with a tree-based approach.
Chaetognatha, benthic species, morphology, biogeography, phylogeny, DNA barcording