title: Ultrastructure of trichocysts in Hematodinium spp. infecting Atlantic snow crab, Chionoecetes opilio.
abstract: Trichocyst morphology and development were explored using transmission electron microscopy in Hematodinium spp. isolated directly from Atlantic snow crab (Chionoecetes opilio) hemolymph and from in vitro cultures. Appearance of trichocysts defines the initiation of a morphological transition in the parasites life cycle from vegetative stage to the transmission stage. Trichocysts within sporonts were found in distinct clusters near the nucleus in close apposition to the Golgi. As cells transitioned to more mature dinospores however, trichocysts were found randomly distributed throughout the cytoplasm. Clusters contained both primordial and maturing trichocysts at various stages indicating an asynchronous development. The random distribution of mature trichocysts suggests deployment to the cell membrane for future extrusion. Mature trichocysts of Hematodinium spp. appeared structurally similar to trichocysts from photosynthetic dinoflagellates. Hematodinium spp. trichocysts differed by the presence of peripheral tubules associated with novel cuboidal appendages in the apical region rather than a network of central electron dense fibres as found in photosynthetic dinoflagellates. Additionally, the trichocyst membrane of Hematodinium spp. was in close apposition to the square crystalline core. Trichocyst expulsion was not observed during our study which along with features of development and maturation within Hematodinium life stages should provide insight into proposed roles in host attachment or defense that could further our understanding of the mechanisms of pathogenesis and transmission of the parasite.
authors: AVC Lobster Science Centre, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada; Department of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: phgaudet@upei.ca.
authors: P H
authors: PH
authors: Gaudet
authors: AVC Lobster Science Centre, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada; Department of Pathology & Microbiology, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: cawthorn@upei.ca.
authors: R J
authors: RJ
authors: Cawthorn
authors: National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Alaska Fisheries Science Center, Resource Assessment and Conservation Engineering Division, 7600 Sand Point Way NE, Seattle, WA 98115, USA. Electronic address: frank.morado@noaa.gov.
authors: J F
authors: JF
authors: Morado
authors: Diagnostic Services, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: wadowska@upei.ca.
authors: D
authors: D
authors: Wadowska
authors: Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: gwright@upei.ca.
authors: G M
authors: GM
authors: Wright
authors: AVC Lobster Science Centre, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada; Department of Biomedical Sciences, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada. Electronic address: sgreenwood@upei.ca.
authors: S J
authors: SJ
authors: Greenwood
mesh_terms: D056893:Alveolata / Q000254:growth & development / Q000502:physiology / Q000648:ultrastructure*; D000818:Animals; D003386:Brachyura / Q000469:parasitology*; D006458:Hemolymph / Q000469:parasitology; D046529:Microscopy, Electron, Transmission
keywords: Chionoecetes opilio; Dinoflagellate; Hematodinium; Trichocyst; Ultrastructure