Histological observations on the development of Ceratomyxa shasta actinosporeans in the polychaete host, Manayunkia speciosa

This study was designed to describe the internal anatomy of the freshwater polychaete, Manayunkia speciosa (Fabriciidae). Understanding the internal anatomy provided insight to then describe the development of the actinospore stage of Ceratomyxa shasta in the polychaete. The first phase of the study focused on six aspects of M. speciosa internal anatomy: (1) integument, (2) musculature, (3) waste processing, (4) nervous system, (5) sensory system, and (6) reproduction. Epidermal width and cellular arrangement of M. speciosa integument varied along the length of the polychaete body. Movement of the polychaete involved the use of longitudinal and oblique musculature. Combined with chaetal bundles and uncini, musculature orientation also provided maneuvering capability. Waste processing was efficient and simplistic. The excretory system included paired nephridia in anterior segments and a simple ciliated gut along the length of the body. Nephridia, located in segments 1 through 3, were approximately 13% of the total body length. The nervous system included a ventral nerve cord that was adjacent to the epidermis and lined with basal cells. Additionally, segments (especially posterior segments) were innervated with chaetal nerves that maintained coordination between musculature and chaetae. The sensory system was composed of nuchal organs (chemoreceptors), statocysts (gravity receptors), and simple ocelli (light receptors). Nuchal organs were internalized, and located within the pre-segmental region of the polychaete. Female M. speciosa had spermathecae or sperm storage organs. Additionally, gonoducts or pores along gamete-bearing segments were involved in the release of eggs from the coelom. The second phase of the study described the life cycle from release of myxospore sporoplasm to mature actinospore for the myxozoan parasite C. shasta in the freshwater polychaete. Infection was initiated through exposure to lab-infected waters. Mature myxospores were present in the gut of segment 4 by 2 hrs post-exposure (PE). Migration of early developmental stages occurred from gut epithelia, though the nervous system, and into the epidermis. Once the parasite reached the epidermis, development typically occurred in segments 6 to 10. All life stages were present, including a proliferative stage (schizogony), development of a pansporocyst (gametogony), sexual reproduction (gametogamy), and spore formation (sporogony). At water temperatures averaging 17.3ºC, schizogony began by 3 hrs PE, gametogony by 14 days PE, gametogamy by 35 days PE, and sporogony between 35 and 49 days PE. Development to a mature actinospore took approximately 49 days PE. Up to 13,650 ± 7,807 actinospores could be released from a single polychaete over a 14-day period. Actinospores appeared to be released directly through the epidermis into the water column.