Gomez-Gutierrez et al. (2006) reported a newly described species of apostome ciliate, Collinia oregonensis n. sp., inhabiting the cephalothorax and abdomen of 3 euphausiid species from the Oregon-Washington coast, including Thysanoessa spinifera. Collinia oregonensis must kill its host to complete its life cycle. Adult euphausiids infected with this parasitoid possess a swollen and bright orange cephalothorax. Given that Thysanoessa spinifera and Euphausia pacifica (which is also infected by this ciliate) together account for about 90% of the euphausiid standing stock in the northern California Current System, this parasitoid ciliate may have a significant impact on euphausiid population abundance, distribution and secondary productivity (Gomez-Gutierrez et al. 2006). This ciliate is the 7th species described for the genus Collinia and the 2nd species known to infect euphausiids. Other apostome ciliates are also known from T. spinifera, such as Gymnodinioides pacifica (Landers et al. 2006 and references therein).
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