Systematic study on the selected groups of marine amphipods (Crustacea: Malacostraca: Peracarida) from Korea

Abstract

For the systematic study of marine amphipods, three groups of amphipods, the sand-burrowing amphipods, the algae-living amphipods, and the amphipods associated with invertebrates, were selected based on their habitat types. Two modern taxonomic methods, the DELTA software and the Digital Drawing, were applied for this thesis. In the first three chapters, the three selected groups of amphipods were examined with morphological taxonomic analyses, respectively. In the last chapter, a molecular taxonomic study was conducted for the species of three selected groups using mitochondrial COI gene sequences in order to confirm the accuracy of morphological classification.As a result of the taxonomic study of sand-burrowing amphipods in chapter 1, 18 species of 6 genera belonging to four families Dogielinotidae, Haustoriidae, Phoxocephalidae, and Urothoidae were identified. Among them, 5 species, Paraphoxus sp., Urothoe sp. 1, Urothoe sp. 2, Urothoe sp. 3, and Urothoe sp. 4, were defined as unknown species, indicating a possibility of new species differing from the congeneric species, and Urothoe convexa was redescribed. Through chapter 2, the taxonomic revision and review of algae-living amphipods, especially of the family Ampithoidae were provided. Three species of the genus Ampithoe, A. lacertosa,Ampithoe new species 1, and Ampithoe new species 2, were described, and the holotype of A. tarasovi collected from Russia was redescribed. A species previously known as A. tarasovi in Korea was newly identified as Ampithoe new species 1, and the description was included. A taxonomic review for all species of the genus Peramphithoe was conducted based on their descriptions and illustrations. The morphological diagnoses and species information were provided additionally. The holotype of P. namhaensis was redescribed, and a new species of the genus was described. In chapter 3, three amphipod species belonging to three families, Melitidae, Pleustidae, and Stenothoidae, were described and information about relationships between the amphipod species and their host invertebrate was provided. Among the three species, Melita anmyeonensis was confirmed to be associated with a bivalve species, Barnea dilatata. Melita anmyeonensis lived between the gills and mantle cavity of B. dilatata. The species could be protected from desiccation and solar irradiation inside the mantle cavity of the host during the low tide period. This was the first record of an association between a species of Melita and a bivalve mollusk. An unknown species of the genus Dactylopleustes was found to be associated with an echinoid species, Mesocentrotus nudus.As obligate associates,the amphipod species was regarded as a new member of the genus Dactylopleustes. Moreover, Metopa groenlandica was collected inside of the cavity of a brachiopod species, and the host brachiopod seemed to provide the amphipod species similar conditions as the bivalve hosts do. The genera Dactylopleustes and Metopa were described for the first time from the Korean fauna. Lastly, the objective of chapter 4 was to test the validity of DNA barcoding as a supplementary tool for species discrimination and to verify anaccuracy of morphological classification of the Korean amphipod species. A 658 bp sequence of COI was obtained from a total of 113 individuals of 27 Korean species (excluding a cryptic species of the genus Urothoe) belonging to 14 genera in 9 families. For Korean amphipod species in this study, a barcode gap was observed for the range between 4% and 9 %. The COI gene confirmed to be an informative molecular marker for species identification. A cryptic species of the genus Urothoe was detected from the species U. convexa.