A myxosporean producing actinospores of the tetractinomyxon type in Hydroides norvegicus Gunnerus (Serpulidae) in Denmark was identified as a member of the family Parvicapsulidae based on small-subunit ribosomal DNA (SSU rDNA) sequences. Myxosporean samples from various Danish and Norwegian marine fishes were examined with primers that detect the novel myxosporean. Sprattus sprattus (Linnaeus) and Clupea harengus Linnaeus (Teleostei, Clupeidae) were found to be infected. The sequences of this parvicapsulid from these hosts were consistently slightly different (0.8% divergence), but both these genotypes were found in H. norvegicus. Disporic trophozoites and minute spores of a novel myxosporean type were observed in the renal tubules of some of the hosts found infected through PCR. The spores appear most similar to those of species of Gadimyxa Køie, Karlsbakk et Nylund, 2007, but are much smaller. The actinospores of the tetractinomyxon type from H. norvegicus have been described previously. In GenBank, the SSU rDNA sequences of Parvicapsulidae gen. sp. show highest identity (82%) with Parvicapsula minibicornis Kent, Whitaker et Dawe, 1997 infecting salmonids (Oncorhynchus spp.) in fresh water in the western North America. A phylogenetic analysis places P. minibicornis and Parvicapsulidae gen. sp. in a sister clade to the other parvicapsulids (Parvicapsula spp. and Gadimyxa spp.).
The life cycle of marine Eubothrium sp. (Cestoda: Pseudophyllidea), from Atlantic salmon (Salmo salar L.) was experimentally completed in one year and included only one intermediate host (Acartia tonsa Dana) (Copepoda: Calanoida). Adult cestodes were collected from farmed salmon, and ripe eggs released by the cestodes were fed to Acartia tonsa. Ingested eggs hatched in the gut and the larvae developed in the haemocoel of the copepod for 15 days at 16°C. A total of 170 seawater-reared salmon were exposed to infected copepods and the total prevalence of Eubothrium sp. in the salmon after infection was 95.3%, with a mean intensity of 15.0 (range 1-87). The infected salmon were kept in the laboratory where the growth of the cestodes was studied for eleven months. Mean length of the cestodes increased with time, but a large variation among the cestodes was observed. Growth and maturation of the cestodes were dependent on host size and the number of worms present in the intestine. No evidence of mortality of Eubothrium sp. was observed during the experimental period.
The fish leech Johanssonia arctica (Johansson, 1898) was collected from king crabs Paralithodes camtschaticus (Tilesius, 1815) in Finnmark, N Norway, and allowed to feed on experimental fish hosts in the laboratory. This leech ingested blood from laboratory-reared cod (Gadus morhua) and halibut (Hippoglossus hippoglossus). Some experimental halibut acquired trypanosome infection, with parasitaemia between ca. 500 and 60,000 trypanosomes ml-1. The trypanosomes were of variable size and measured 39-90 µm (mean 57 µm) ca. 81 days post-infection. Characteristic features are cell striation, refractile cytoplasmic granules, anterior nucleus and a relatively long (ca. 6 µm, max 9 µm) distance from the posterior end to the kinetoplast. Following growth, the trypanosomes became increasingly slender, with fewer striae and a nucleus position less pronounced anterior. The trypanosome is considered distinct from a type transmitted by the leech Calliobdella nodulifera (Malm, 1863) in the NE Atlantic, but is regarded conspecific with a trypanosome transmitted by J. arctica in the NW Atlantic. This trypanosome has in the past been identified as Trypanosoma murmanensis Nikitin, 1927, a poorly described species. T. murmanensis cannot be recognized with certainty among the trypanosomes transmitted by C. nodulifera and J. arctica respectively. We propose that the J. arctica-transmitted species is considered T. murmanensis Nikitin, 1927 sensu stricto.
Sequencing of SSU rDNA showed that actinospores of the tetractinomyxon type, which develop in Chone infundibuliformis Krøyer (Annelida, Polychaeta, Sabellidae) from the northern Øresund, Denmark, are identical with Ceratomyxa auerbachi Kabata, 1962 (Myxozoa, Ceratomyxidae). This myxosporean was found in the gallbladder of the Atlantic herring Clupea harengus L. from the northern Øresund, Denmark, and from the Bergen area, western Norway. The pansporocysts and actinospores of C. auerbachi are described. This is the third elucidated two-host life cycle of a marine myxozoan, and the first involving a marine ceratomyxid.