The Histology of a Siphonophore - Nanomia bijuga

A few weeks back, we posted a stunning video of Siphonophore living deep in the ocean (pelagic) -

Anyone watching the video says double wow, when he realizes that the odd creature is not one multicellular animal, but a colony of multi-cellular animals (edited). Siphonophores play unique role in evolution of multicellular animals, and we also mentioned Casey Dunn’s interesting work on trying to understand them at the molecular level.

Today we came across a bioarxiv paper by his group that the readers may find interesting.

The siphonophore Nanomia bijuga is a pelagic hydrozoan (Cnidaria) with complex morphological organization. Each siphonophore is made up of many asexually produced, genetically identical zooids that are functionally specialized and morphologically distinct. These zooids predominantly arise by budding in two growth zones, and are arranged in precise patterns. This study describes the cellular anatomy of several zooid types as well as of the stem and gas-filled float, called the pneumatophore. The distribution of cellular morphologies across zooid types enhances our understanding of zooid function. The unique absorptive cells in the palpon, for example, indicate specialized intracellular digestive processing in this zooid type. Furthermore, there are multiple areas of both endodermal and ectodermal epithelial complexity. Though cnidarians are usually thought of as mono-epithelial, we characterize at least two cellular populations in this species which are not connected to a basement membrane. This work provides a greater understanding of epithelial diversity within the cnidarians, and will be a foundation for future studies on Nanomia bijuga, including functional assays and gene expression analyses.

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