West L, Powers D
Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950.
Mol Mar Biol Biotechnol. 1993 Mar-Apr;2(2):71-5.
Although it is generally accepted that the first multicellular organisms arose from unicellular ancestors, the phylogenetic relationships linking these groups remain unclear. Anatomical, physiological, and molecular studies of current multicellular organisms with relatively simple body organization suggest key characteristics of the earliest multicellular lineages. Glass sponges, the Hexactinellida, possess cellular characteristics that resemble some unicellular protistan organisms. These unique sponges were abundant in shallow seas of the early Cambrian, but they are currently restricted to polar habitats or very deep regions of the world oceans. Due in part to their relative inaccessibility, their potential significance to the early phylogeny of the eukaryotic kingdoms has been largely overlooked. We used sequences of the 18s ribosomal RNA gene of Farrea occa, a representative of the deep-water hexactinellid sponges, and Coelocarteria singaporense, a representative of the more common demosponges, and compared them with selected ribosomal RNA gene sequences available within the Protista. Using four computational methods for phylogenetic analysis of ribosomal DNA sequences, we found that the hexactinellid sponge-demosponge cluster is most closely related to Volvox and Acanthamoeba.
尽管人们普遍认为最早的多细胞生物起源于单细胞祖先，但连接这些类群的系统发育关系仍不明确。对当前身体结构相对简单的多细胞生物进行的解剖学、生理学和分子研究揭示了最早多细胞谱系的关键特征。玻璃海绵，即六放海绵纲，具有一些类似于单细胞原生生物的细胞特征。这些独特的海绵在寒武纪早期的浅海中大量存在，但目前仅限于极地栖息地或世界海洋的极深区域。部分由于它们相对难以获取，它们对真核生物早期系统发育的潜在意义在很大程度上被忽视了。我们使用了深水六放海绵纲的代表物种奥氏远海海绵（Farrea occa）和更常见的寻常海绵纲的代表物种新加坡腔海绵（Coelocarteria singaporense）的18s核糖体RNA基因序列，并将它们与原生生物界中可用的选定核糖体RNA基因序列进行了比较。使用四种核糖体DNA序列系统发育分析的计算方法，我们发现六放海绵纲-寻常海绵纲聚类与团藻属和棘阿米巴属关系最为密切。
