Systematics of ‘lithistid’ tetractinellid demosponges from the Tropical Western Atlantic – implications for phylodiversity and bathymetric distribution. Lithistid Sponges from the Tropical Western Atlantic

Background Among all present demosponges, lithistids represent a polyphyletic group withexceptionally well preserved fossils dating back to the Cambrian. Knowledge of their recentdiversity, particularly in the Tropical Western Atlantic Ocean (TWA) where they are commonin deep waters, is scarce making any comparison between present and past major ‘lithistid’faunas difficult. In addition, the lack of sufficient molecular and morphological data hamper anypredictions on phylogenetic relationships or phylodiversity from this region. The Harbor BranchOceanographic Institute (HBOI, Fort Pierce, Florida) holds the largest collection of TWA lithistidsponges worldwide, however, the majority remain to be taxonomically identified and revised.Methods/Principal Findings In this study we provide sequences of 249 lithistid demo-sponges using two independent molecular markers (28S rDNA (C1-D2) and cox1 mtDNA). Inaddition, a morphological documentation of 70 lithistid specimens is provided in the databaseof the Sponge Barcoding Project (SBP). This integrated dataset represents the largest andmost comprehensive of the TWA lithistids to date. The phylogenetic diversity of ‘lithistid’demosponges in the Bahamas and Jamaica are high in comparison to other TWA regions;Theonellidae and Corallistidae dominate the fauna, while Neopeltidae and Macandrewiidae arerare. A new tetractinellid suborder, one new genus and several new species are recognizedand the Pacific ‘lithistid’ genera, Herengeria and Awhiowhio, are reported from the TWA for thefirst time. The higher-taxa relationships of desma-bearing tetractinellids are discussed andtopics for revision suggested.Conclusion This first integrative approach of TWA ‘lithistid’ demosponges contributes to abetter understanding of their phylogenetic affinities, diversity and bathymetric distribution pat-terns within the TWA. As in the Pacific, the TWA ‘lithistid’ demosponges dominate deep-waterhabitats. Deeper taxonomic investigations will undoubtedly contribute to a better comparisonbetween present major ‘lithistid’ faunas and their fossil record in the Mesozoic.

背景：在现生寻常海绵（demosponges）类群中，石海绵类（lithistids）属于一多系群，其化石记录可追溯至寒武纪，且保存状态极为完好。目前学界对该类群现生多样性的认知较为匮乏，尤其是在深水环境中分布广泛的西热带大西洋（Tropical Western Atlantic Ocean, TWA）区域，这使得难以对比现代与远古的主要石海绵动物群。此外，该区域缺乏足够的分子与形态学数据，阻碍了对其系统发育关系与系统多样性的预测。佛罗里达州皮尔斯堡的哈勃分支海洋学研究所（HBOI）拥有全球规模最大的西热带大西洋石海绵标本馆藏，但其中绝大多数尚未完成分类学鉴定与修订工作。

方法与主要结果：本研究通过两个独立的分子标记（28S核糖体DNA（28S rDNA，C1-D2区）与细胞色素c氧化酶亚基I线粒体DNA（cox1 mtDNA）），获取了249株石海绵类寻常海绵的序列数据。此外，本研究还为70份石海绵标本完成了形态学记录，并将其上传至海绵条形码项目（SBP）的数据库中。该整合数据集是目前全球针对西热带大西洋石海绵类群规模最大、内容最全面的数据集。与西热带大西洋其他区域相比，巴哈马与牙买加海域的石海绵类寻常海绵系统多样性水平更高；其中球海绵科（Theonellidae）与梳海绵科（Corallistidae）为该区域的优势类群，而新皮海绵科（Neopeltidae）与Macandrewiidae科则较为罕见。本研究确立了1个新的四放海绵亚目（tetractinellid suborder）、1个新属以及多个新种；此外，首次在西热带大西洋区域报道了太平洋石海绵类群——赫伦海绵属（Herengeria）与阿维奥海绵属（Awhiowhio）。本研究还探讨了具脱骨针（desma）的四放海绵类群的高级阶元系统发育关系，并提出了后续修订的研究方向。

结论：本研究首次针对西热带大西洋石海绵类寻常海绵开展整合性研究，有助于加深学界对该区域内其系统发育亲缘关系、物种多样性以及水深分布模式的认知。与太平洋海域的情况一致，西热带大西洋的石海绵类寻常海绵为深水生境的优势类群。后续开展更深入的分类学研究，无疑将有助于更好地对比现代主要石海绵动物群与其中生代的化石记录。