ABSTRACT
Ascidians are solitary or colonial marine invertebrates that share a common ancestor with vertebrates and belong to the phylum Chordata. Colonial ascidians include more than 1,700 species and are a highly varied group in terms of sizes, shapes, colors and geographical locations. Here we discuss one of the most-studied model species, Botryllus schlosseri, as a most suitable representative of colonial ascidians. Botryllus was first described four centuries ago but has been studied extensively just in the past seven decades, revealing a promising model for diverse biological disciplines. This chapter details the history of the research, biology and geographical distributions of this cosmopolitan species. Special attention is devoted to several unique phenomena staging this species as a model system in biology, such as the continuous life and death cycles of colonial modules (blastogenesis), the capacity for whole-body regeneration and the unique self/non-self recognition (histocompatibility) resulting in either natural immunological rejection or chimerism. The description is followed by with current applications, the development of tools and the description of several leading scientific challenges. Following the wide range of phenomena developing in Botryllus, it is anticipated that this species will become a central model in biology. Working with B. schlosseri may reform and shift dogmas in biology.
