Morphological and molecular analysis of <i>Ephydatia fluviatilis</i> (Porifera: Spongillida: Spongillidae) from Nanjing, China

We present a comprehensive morphological description of <i>Ephydatia fluviatilis</i> collected in Nanjing for the first time in studies of freshwater sponges in China, based on scanning electron micrography of the sponge meshwork, the megascleres, the gemmules, and the delicate gemmuloscleres, in comparison with relevant data reported worldwide. The morphotype revealed in this study shows a peculiar spicular complement of the skeleton composed of two types of megascleres (the normal oxeas and occasional styles) with abundant tiny, centrally distributed microspinoses, gemmules (ca. 440 μm in diameter) bearing two types of spinose decoration on the shaft (i.e., erect long spines and microspinoses). We report the first complete ITS sequences of the morphotype of <i>E. fluviatilis</i> from China, which, combined with homologous sequences of related taxa from GenBank, are used in a phylogenetic analysis in order to understand the species relationship within <i>Ephydatia</i> and neighbouring taxa. Combining the ITS phylogeny and the gemmulosclere morphotypes, we identify three clades in the paraphyletic genus <i>Ephydatia</i> that are distinguished by different birotule gemmulosclere morphotypes for gemmule-bearing species. Multiple losses of gemmules within endemic taxa, as previously proposed, are confirmed in this study in a phylogenetic context obtained herein. Additionally, genetic similarities are found in some morphologically diverse species, likely indicating recent endemism leading to morphological specialization. Considering the diverse fossil record of <i>Ephydatia</i> from Cenozoic sedimentary strata of wide geographic ranges, we hypothesize that <i>Ephydatia</i> might have a deep root in the Paleogene or earlier and experienced a rapid, Quaternary radiation with emergences of specialized endemic species that lost gemmules under glacial-interglacial paleoenvironment.本研究针对中国淡水海绵研究领域首次在南京采集的溪栖河海绵（Ephydatia fluviatilis）开展全面形态学特征描述，研究基于该海绵的骨针网、大形骨针（megascleres）、芽球（gemmules）以及纤细的芽球骨针（gemmuloscleres）的扫描电子显微成像（scanning electron micrography），并与全球已报道的相关数据进行比对。本研究揭示的该物种形态型拥有独特的骨骼骨针组合：其骨骼包含两种大形骨针（正常直形骨针与偶见的单端尖骨针），且分布有大量细小的中央微棘（microspinoses）；其芽球直径约为440μm，外壁带有两种棘状纹饰——直立长棘与微棘。本研究报道了中国境内溪栖河海绵（Ephydatia fluviatilis）该形态型的首个完整内转录间隔区（Internal Transcribed Spacer, ITS）序列；研究将该序列与从基因银行（GenBank）获取的相关类群同源序列相结合，开展系统发育分析（phylogenetic analysis），以阐明河绵属（Ephydatia）及其近缘类群的物种间亲缘关系。结合内转录间隔区系统发育树与芽球骨针形态型特征，本研究在并系属河绵属（Ephydatia）中识别出三个演化支（clades），这些演化支可通过产芽球物种的双轮芽球骨针（birotule gemmulosclere）形态型差异进行区分。本研究在本次获得的系统发育框架下，证实了此前提出的、特有类群中多次出现芽球丢失的演化事件。此外，本研究在部分形态多样性较高的物种中发现了遗传相似性，这可能暗示近期的特有化进程催生了形态特化。考虑到河绵属（Ephydatia）在全球广泛分布的新生代（Cenozoic）沉积地层中拥有多样的化石记录，本研究提出如下假说：河绵属可能起源于古近纪（Paleogene）或更早的地质时期，并在第四纪（Quaternary）经历了快速辐射演化，期间演化出了在冰期-间冰期古环境（glacial-interglacial paleoenvironment）下丢失芽球的特化特有物种。