Pyrosomida

Pyrosomida is an order of pelagic colonial tunicates within the class Thaliacea. Members form transparent, hollow colonies that can take on cylindrical or funnel-shaped shapes and may reach considerable lengths. The colony is composed of many individual zooids that are genetically identical and connected by a shared tunic and interior digestive system, functioning as a single, cohesive organism.

Colonies are typically built from numerous zooids arranged along a central canal. They possess incurrent and excurrent openings to draw in seawater, filter food particles such as phytoplankton and microzooplankton, and expel processed water. Each zooid resembles a small tunicate, but cannot survive independently when part of the colony. The feeding and locomotion of the entire colony are coordinated through the shared body plan and the flow of water through the colony’s internal system.

Pyrosomes are known for bioluminescence; they emit blue light when stimulated, a trait that has given rise to their name, which derives from the Greek for fire. This light production is a characteristic feature of many colonies observed in the open ocean.

Distribution and habitatally, Pyrosomida occur in pelagic environments worldwide, with a higher prevalence in tropical and subtropical seas. They are typically found in the upper water column, from the surface down to several hundred meters, and can form drifting blooms. Mass occurrences or strandings on beaches can occur, particularly after storms or strong currents.

Taxonomy and species: Pyrosomida is an order within Thaliacea, alongside other orders such as Salpida and Doliolida. Notable species within the genus Pyrosoma include Pyrosoma atlanticum and Pyrosoma giganteum, both of which form large, leaf- to tube-like colonies in the oceans.