Terrestrial ciliates (Protozoa,Ciliophora) from two islands (Gough,Marion) in the southern oceans,with description of two new species,Arcuospathidium cooperi and Oxytricha ottowi

Twenty-seven soil and moss samples from Gough Island (40°21′S, 09°53′E) and Marion Island (46°52′S, 37°51′E), two small volcanic elevations in the South Atlantic and southern Indian Oceans, were investigated for ciliated protozoa using the non-flooded Petri dish method. Collections were made from a variety of biotopes covering most principal soil and vegetation types. Sixty species were found, 39 on each of the two islands studied; all are first records for these regions. The mean number of species per sample was markedly higher on Gough (14) than on Marion Island (5.7), reflecting increased climatic severity and decreased soil fertility, respectively. Grassland with a well developed soil cover supported more species than sites with sparse vegetation or heavily eutrophic penguin-influenced habitats. Colpodids dominated the frequency spectrum due to their r-selected survival strategy. The most common species were Colpoda steinii, a euryoecious bacteria feeder, and Pseudoplatyophrya nana, an obligate fungal sucker, also belonging to the Colpodea. Species were very patchily distributed, probably due to the environmental severity allowing few pioneers to establish stable populations. Hemimastix amphikineta, a peculiar heterotrophic flagellated organism, was found on Gough Island, an observation that supports the restricted Gondwanian distribution previously proposed for this species. Two new species were found. Arcuospathidium cooperi n. sp., a gymnostome ciliate, was discovered on Marion Island and belongs to a small group of spathidiids lacking extrusomes. Oxytricha ottowi n. sp., a hypotrichous ciliate, was discovered on Gough Island and is unique in having eight macronuclear nodules.