The complete mitochondrial genome of Saccostrea Kegaki (Pterioida, Ostreidae)

The complete mitochondrial genome of the tropical oyster Saccostrea echinata (Bivalvia: Ostreidae) from the South China Sea

Saccostrea echinata is a rock perched oyster with wide distribution and tremendous potential for commercial mariculture. However, the taxonomy of this genus is confused. In this study, we described the complete mitochondrial genome of medium-sized form of Saccostrea echinata. The genome is 16,282 bp in length, encoding the standard set of 12 protein-coding genes (PCGs), 23 tRNA genes, and two rRNA genes, with circular organization. The overall base composition of the whole mitochondrial genome was A (26.78%), T (36.64%), G (21.99%), and C (14.59%) with an AT bias of 63.42%. The longest PCG of these species was ND5, whereas the shortest was ND4L.

Revision shock in Pacific oysters taxonomy: the genus Magallana (formerly Crassostrea in part) is well-founded and necessary

The description of the genus Magallana provoked taxonomic ‘revision shock’ among Bayne and colleagues, who criticised: (1) the supporting evidence for this taxonomic change, (2) the procedure used and (3) its impact on the nomenclatural stability of oysters. Here, we demonstrate that the description of the genus Magallana fulfils the norms of taxonomic and indexing revisions, and is well-founded on a scientific basis. The clade named Magallana is supported by a robust phylogeny based on comprehensive taxon sampling, independent datasets and varied analytical methods. A new maximum likelihood phylogenetic analysis of oysters, based on mitochondrial gene order data (representing molecular phenotypes above the sequence level), has provided additional support for this classification. These results are fully consistent with all previously published phylogenetic studies, thus providing an unambiguous indication of the stability of the clade that meets all the currently accepted criteria for naming clades as taxa. We show that, while the criterion of ‘morphological diagnosability’ is not applicable at any level of oyster classification, several striking molecular phenotypes are diagnostic of Magallana, both at the nuclear and the mitochondrial genome level. The classification with three genera Magallana, Crassostrea and Talonostrea reflects the evolutionary diversity of Crassostreinae and is consistent with taxonomic ranking criteria adopted for other oyster subfamilies.

Temporal changes in hemocyte functions of the oyster Saccostrea kegaki (Torigoe & Inaba, 1981) on Jeju Island off the south coast of Korea are closely associated with annual gametogenesis

Hemocyte parameters have been used as a proxy to characterize the health condition of marine bivalves, as the effects of external and internal stresses are reflected well in these parameters. Marine bivalve hemocyte functions are often depressed during the post-spawning period due to physiological stress and energy depletion. In this study, we analyzed temporal changes in hemocyte parameters of the oyster Saccostrea kegaki on Jeju Island, off the south coast of Korea, using flow cytometry. Total hemocyte count (THC), hemocyte types, hemocyte mortality, and phagocytosis capacity were analyzed. S. kegaki spawned during June and August, when the sea surface temperature increased from 18 to 23 °C. Most of the oysters were in the spent and resting phases from September to January. THC dropped dramatically from September to October, when most oysters completed spawning. Histology revealed that the residual eggs or sperm were actively resorbed through phagocytosis by hemocytes during the spent stage. Hemocyte mortality also showed its annual peak in October, possibly due to increased resorbing activities. The phagocytosis capacities of the granulocytes decreased dramatically from September to February. The level of energy reserves (glycogen) in post-spawning tissues was significantly lower than that prior to spawning. The low energy level reserve during the post-spawning period likely reduced the THC and immune capacities, as oysters may have been unable to acquire sufficient food from the ambient environment.