Chaetognatha

There are currently two recognized orders of chaetognaths: (i) Phragmophora, with the planktonic genera Eukrohnia, and Heterokrohnia; the benthoplanktonic genus Archeterokrohnia; and the benthic genera Spadella, Paraspadella, Hemispadella, Calispadella, Bathyspadella, and Xenokrohnia; and (ii) Aphragmophora, with the planctonic genera Krohnitta, Pterosagitta and Sagitta. In this leaflet, the genus Sagitta is not divided into several genera. This taxonomic division is based on revisions by Ritter-Zahony (1911) and Tokioka (1956). More recent information can be found in Bone et al. (1991), Casanova (1999), and Pierrot-Bults (2017).
This is a major revision of ICES Identification Leaflets for Plankton No. 1 (Fraser, 1939; revised by Fraser, 1957). It covers the 28 of the 41 planktonic species recognized in the ICES Area. Excluded are 12 species of the very deep living genus Heterokrohnia and Sagitta abyssicola, all occurring below approximately 2000 m.