Spadella

Spadella is a genus of small, transparent marine invertebrates belonging to the family Spadellidae within the phylum Chaetognatha, commonly known as arrow worms. Unlike most chaetognaths, which are pelagic (free-swimming in open water), species of Spadella are benthic, meaning they live near the seafloor and often attach to substrates in shallow marine environments.

The first recorded observation of a Spadella species was made by Busch in 1851, when Spadella cephaloptera was first reported. However, the genus itself was formally described by Langerhans in 1880, and currently includes several recognized species.

Spadella species play an important role in marine food webs, preying on copepods and other planktonic organisms. They have also been of scientific interest due to their unique evolutionary traits, particularly in the context of bilaterian phylogeny and Hox gene organization, which has led to debates on the evolutionary origins of chaetognaths.