University of Tasmania, Australia

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Von Ritter-Záhony 1909


Superphylum Deuterostomia
Phylum Chaetognatha
Class Sagittoidea
Order Aphragmorphora
Family Sagittidae
Genus Sagitta


  • Maximum adult body length: 105 mm; tail: 10-18 % of body length.

Distinguishing characteristics

  • Chaetognaths belong to an exclusively marine phylum commonly known as arrow worms.
  • There are around 100 species in the phylum, of which 10 are known from south-east Australian waters.
  • They are mostly holoplanktonic predators on copepods and other crustaceans but there are a few benthic forms.
  • The head bears 1 or 2 rows of sharp spines.
  • Posterior to these are a paired lateral group of grasping spines (‘jaws’).
  • The transparent body bears one or two pairs of lateral fins and the tail bears a caudal fin.
  • Sagitta minima can be recognised by its small size (ca. 6 mm), and short ovaries.
  • Sagitta serratodentata reaches 17.5 mm.
  • Sagitta gazella reaches 53 mm. They can be identified on the basis of the shape and arrangement of the lateral fins.


  • Sagitta minima is common in the south-east Australian region, occurring almost throughout the year in estuarine, inshore coastal, coastal and oceanic waters (Nyan Taw, 1975).
  • Sagitta serratodentata tasmanica has been recorded from inshore coastal waters of south-east Australia (Thomson, 1947) and Tasmania (Nyan Taw, 1978).
  • There are several sub-species that may co-exist. Separating these requires well-preserved adults since it depends on the form of the mature seminal vesicles.
  • Sagitta gazellae has a circum-global distribution restricted to the north by the sub-tropical convergence (region where sub-tropical and sub-Antarctic currents meet), and to the south by the Antarctic neritic zone. Therefore, although common in oceanic waters off the east coast of Tasmania, it is not found in the sub-tropical regions further north.


  • A wholly marine group.
  • They are hermaphrodites, each bearing large paired ovaries and testes.
  • Development is direct.
  • All are strongly carnivorous feeding primarily on copepods.
  • Known to undertake diel vertical migration to track the vertical movements of their prey.
  • Alternately float and swim by means of a series of rapid flicks of the post-anal tail in the dorsoventral plane.
  • Lateral fins act as stabilisers.
  • Prey capture is by a series of movable spines flanking the mouth.