Arrow worms of the family Sagitta
(about 6 specie in scandinavian waters)

Sagitta elegans 3,0 kB

Distribution in scandinavian waters

Maximum length: One specie (Sagitta maxima) can be as long as 9cm. Compare with a finger.
Appearance: Uncoloured and transparent. On the side of the head are a pair of rows of curved grasping spines. From the anterior (on the middle of the body) to the tail are a pair of lateral fins. The eyes of Sagitta are black and evident. Compare Sagitta with the arrow worms of the group Eukrohnia.
Depth: From the surface to a depth of several hundred metres.
Environment: Pelagic.
Misc: Arrow worms are very effective predators that can catch and kill broods of their own size. They are fast swimmers and are able to puncture the external skeleton of their prey with their bristles and teeth and there after inject poison. Besides broods, they eat many of the other creatures that inhabit pelagic waters, such as krill, ghost shrimps, copepods, medusae and other arrow worms. The most important ingredient in their diet are copepods. Many of the above prey are themselves predators and eat amongst other things, arrow worms.
    Every arrow worm developes both male and female sexual organs. The male organs develope first, but they seldom fertilize themselves although they carry sperm and eggs at the same time. Fertilized eggs are released directly into the water where they develope directly (without a larva stage) into arrow worms.
Classification: The family Sagitta is part of the group chaetognatha. The two specie that are most common in Swedish waters are Sagitta setosa and Sagitta elegans. Sagitta elegans is shown in the picture above.

Sagitta     Other names

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson