Self-splicing mitochondrial introns are a rarely reported phenomenon in animals, with a sparse and uneven distribution confined to some species of sponges, corals, placozoans, and a single species of annelid. Here, we describe a mitochondrial intron present only in some populations of Phakellia robusta, a sponge distributed across the North-east Atlantic deep-sea. The mitochondrial intron of P. robusta was detected in the position 387 of the COI gene and classified as a Group I intron of class IB. Interestingly, this intron was only detected in the shallower populations of P. robusta from Ireland to Norway, spanning 1000 km and was absent in deeper samples of the species. Such deeper populations have recently been proposed to be the result of hybridization between P. robusta and its congeneric Phakellia hirondellei. We propose that this past hybridization might be behind the absence of the intron in the specimens of P. robusta occurring at deep waters. Our analyses indicate that the intron detected in P. robusta might have a double origin (most likely fungi and other organism), as it has previously suggested for the sponge Stupenda singularis. BLAST searches produced matches with the homing endonuclease gene (HEG) nested within the S. singularis intron and this HEG belongs to the family of LAGLIDADG homing endonucleases (LHEs). The evolutionary relevance of the presence/absence of this intron for this species needs to be determined and potential adaptive advantages should not be ruled out.

自分裂线粒体内含子在动物中很少报道，分布稀疏且分布不均，仅限于某些种类的海绵，珊瑚，角虫和单个类的网纹动物。在这里，我们描述了仅在部分Phakelliarobusta种群中存在的线粒体内含子，Phakelliarobusta遍及东北大西洋深海。在COI基因的387位检测到了强壮疟原虫的线粒体内含子，并将其归类为IB类的I组内含子。有趣的是，此内含子在较浅群仅检测P.罗布斯塔从爱尔兰到挪威，跨度超过1000公里，并且在该物种的更深层样本中不存在。这种更深层次的人群，近年来，提出要与杂交的结果P.罗布斯塔及其同类Phakellia hirondellei。我们建议，这种过去的杂交可能是在深水区的强壮假单胞菌标本中缺少内含子的背后。我们的分析表明，在所检测的内含子P.罗布斯塔可能有双重起源（最有可能的真菌和其他生物体），因为它以前的海绵建议Stupenda辛格拉里斯。BLAST搜索产生了与嵌套在奇异链球菌中的归巢核酸内切酶基因（HEG）相匹配的结果内含子，该HEG属于LAGLIDADG归巢核酸内切酶（LHE）家族。需要确定该内含子与该物种存在/不存在的进化相关性，不应排除潜在的适应性优势。