Labyrinthuloides haliotidis n.sp. (Protozoa: Labyrinthomorpha), a pathogenic parasite of small juvenile abalone in a British Columbia mariculture facility

Abstract

Labyrinthuloides haliotidis n.sp. is an achlorophyllous eucaryotic protist that is pathogenic to juvenile abalone (Haliotis kamtschatkana and Haliotis rufescens) less than 190 days of age (postsetting). Within the muscle and nervous tissue of the head and foot of susceptible abalone and in axenic nutrient culture media at 10 °C, vegetative stages of L. haliotidis proliferated by binary fission and produced ectoplasmic nets from sagenogenetosomes located on the cell periphery. When the abalone died and the parasites were released from the decaying tissue or when culture forms were washed free of nutrient medium and placed in sea water, internal multiple fission (sporulation) occurred within some cells, producing zoosporoblasts. After 24 to 72 h of incubation at 10 °C, the zoosporoblasts ruptured to release from 3 to about 10 infective biflagellated zoospores. After about 24 h of active swimming, or on contact with a glass surface, the zoospores shed their flagella. Ultrastructure of vegetative stages and zoospores related this species more closely to the thraustochytrids than to the labyrinthulids. Confusion still prevails concerning the higher taxonomic affinities of this group of organisms. In keeping with recent publications on the taxonomy of the kingdom Protozoa, L. haliotidis was considered to be a protozoan of the phylum Labyrinthomorpha and not allied with the fungi.