Abstract
The occurrence of the sandy beach mysids Archaeomysis spp. (Mysidacea) with epibiontic peritrich ciliates (Protozoa) has been studied. Epibiontic peritrich infestations were found on four Archaeomysis species collected from the western North Pacific. This study provided the evidence of existence of a previously undescribed symbiontic association between mysids and epibiontic ciliates. Overall incidence of infestation for Archaeomysis sp., A. kokuboi, A. vulgaris, and A. japonica hosting peritrichs averaged 74.7, 75.6, 22.3, and 1.2%, respectively, with higher incidence in the northern populations for the genus. No mysids carrying peritrichs were found in specimens taken from central to southwestern Japan. Thus, the attached ciliates were considered to have a cold water affinity. Seasonal observations over one year suggested that the mysid-ciliate association in the northern waters of Japan was a year-round phenomenon. The incidence of infested mysids in the harsh zone of sandy beaches was noticeably higher than that in the infralittoral bottoms, suggesting that the habitat of host mysids may be a factor affecting the infestation success of the peritrichs.
