Gymnodinioides pitelkae n. sp. (Ciliophora, Apostomatina) from the littoral amphipod, Marinogammarus obtusatus, a trophont with remnants of the tomite's infraciliature

The apostome genus, Hyalophysa, is a symbiont on most littoral decapods in the US, but no other crustacean orders have been investigated. When exuvia of the amphipod Marinogammarus obtusatus were examined, they contained swimming trophonts whose characteristics revealed by Chatton-Lwoff stains describe a new species of Gymnodinioides. Its unique characteristic is the retention in the trophont of a polykinety similar to the falciform field of the tomite, the non-feeding, migratory microstome stage common to apostome genera. The trophont's anterior pattern of kineties also resembles that of the tomite. Speculations that speciation in Gymnodinioides may result from isolation on different hosts, changes in the internal feeding apparatus, delays or mishaps during morphogenesis, or habitat changes affecting the host must consider the case of G. pitelkae. The tomite may not respond to the signals from its premoult host to change to the macrostome infraciliature although the feeding apparatus is formed.