Aggregata sinensis n. sp. (Apicomplexa: Aggregatidae), a new coccidian parasite from Amphioctopus fangsiao and Octopus minor (Mollusca: Octopodidae) in the Western Pacific Ocean.

A new species of parasitic Aggregata, Aggregata sinensis n. sp., is described from the octopuses Amphioctopus fangsiao (d'Orbigny, 1839-1841) and Octopus minor (Sasaki, 1920) (Mollusca: Octopodidae) in China based on morphological data and 18S ribosomal RNA (rRNA) gene sequences. The sexual gamogonic and sporogonic stages of the parasite were observed under light microscope. The sizes of oocysts were 207.35-618.74 μm in length and were 136.31-420.68 μm in width. Oocysts were fully sporulated and were shaped spherically or irregularly. Mature sporocysts within oocysts were spherical or slightly subovoid and were 19.42-22.32 μm in length and 19.12-21.55 μm in width. Sporozoites were typically spiral within sporocysts and were 17.81-24.90 μm long and 2.05-3.42 μm wide. Molecular phylogenetic analysis constructed using the 18S rRNA gene sequences supports the morphological classification that our species is placed within the genus Aggregata. Moreover, the sequence belonged to the genus Aggregata. However, the 18S rRNA gene sequence of Ag. sinensis was significantly different from that of other Aggregata available currently. Ag. sinensis is the first two-host parasitic species of Aggregata reported from definitive host Am. fangsiao and O. minor and is the only species of the genus Aggregata known in Western Pacific waters.