X-cells were first described as an unknown cell type in northern hemisphere flatfish in 1969. Almost a decade later they were described in an Antarctic fish, the bald notothen Trematomus borchgrevinki, thus demonstrating their global distribution. Since this time, X-cells from various northern hemisphere fish species and from three other Antarctic fishes, the emerald notothen Trematomus bernacchii, the crowned notothen Trematomus scotti, and the painted notothen Nototheniops larseni have been identified as perkinsozoan parasites of the Family Xcellidae. Currently there are seven X-cell species described within this family. Here we report the morphology of X-cells isolated from the gill filaments of the bald notothen and include details of some of its division forms. Using short-read high-throughput DNA sequencing technology we have sequenced, assembled, and verified a 5347-bp region of the X-cell rRNA repeat unit that includes the complete 18S gene. In all cases, phylogenetic analyses identified this sequence as a distinct taxon and placed it among the perkinsozoan alveolates alongside other previously identified species in the X-cell family. Using a combination of morphological and genetic evidence we now describe a new X-cell genus and species, Cryoxcellia borchgrevinki gen. nov., sp. nov., from McMurdo Sound, Antarctica.

X 细胞于 1969 年首次被描述为北半球比目鱼中的一种未知细胞类型。将近十年后，它们在南极鱼（秃头 notothen Trematomus borchgrevinki）中被描述，从而证明了它们的全球分布。从那时起，来自北半球各种鱼类和其他三种南极鱼类的 X 细胞，即 emerald notothen Trematomus bernacchii、crowned notothen Trematomus scotti和 painted nototheniops larseni已被确定为 Xcellidae 科的 perkinsozoan 寄生虫。目前，该家族中描述了七种 X 细胞。在这里，我们报告了从秃头 notothen 的鳃丝中分离出来的 X 细胞的形态，并包括了它的一些分裂形式的细节。我们使用短读高通量 DNA 测序技术对包含完整 18S 基因的 X 细胞 rRNA 重复单元的 5347-bp 区域进行了测序、组装和验证。在所有情况下，系统发育分析都将此序列确定为一个独特的分类单元，并将其与之前在 X 细胞家族中确定的其他物种一起置于 perkinsozoan 肺泡中。结合形态学和遗传学证据，我们现在描述了一个新的 X 细胞属和种，Cryoxcellia borchgrevinki将军 十一月，sp。十一月，来自南极洲麦克默多海峡。