''Parasagitta elegans'' is a small

arrow worm The Chaetognatha or chaetognaths (meaning ''bristle-jaws'') are a phylum of predatory marine worms that are a major component of plankton worldwide. Commonly known as arrow worms, about 20% of the known Chaetognatha species are benthic zone, be ...

in the family

Sagittidae Sagittidae is a family of sagittoideans in the order Aphragmophora. Genera *'' Aidanosagitta'' Tokioka & Pathansali, 1963Tokioka, T. & Pathansali, D. (1963). Another new chaetognath from Malay waters, with a proposal of grouping some species of ...

, previously named ''Sagitta elegans''

Morphology

''Parasagitta elegans'' (prev. ''Sagitta elegans''). Body of adult animal can grow up to 45 mm, is narrow, firm and opaque (this image: animal very see-through. Visible opaque animal needs better picture). Fins are separated, rounded, and completely rayed. Anterior fins beginning below the ventral ganglion. Alimentary diverticula present. Eyes with small, round pigment spot. Ovaries long and narrow. Seminal vesicles conical in shape, either exactly next to or very close to the tail fin, separated from posterior fins. For anatomy, reproduction, classification, and fossil record; see Chaetognatha

Taxonomy

Three subspecies are recognised - ''Sagitta elegans arctica'', ''Sagitta elegans baltica'' and ''Sagitta elegans elegans''. The subspecies are considered to vary in size depending on the temperature of the waters in which they develop, which could be an indication of them being synonymous species. The numbers of hooks and teeth vary slightly in the three subspecies.

Ecology

General

With exception for the

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

species ''Spadella'', arrow worms are all adapted for planktonic existence. They swim to the surface at night when it is safer for them to hunt, and descend during daytime. Most of the time they drift passively, but they can dart forward in swift spurts, using their caudal fin and longitudinal muscles. Horizontal fins bordering the trunk serve largely as stabilizers, and are used in flotation rather than in active swimming.

Distribution

''Parasagitta elegans'' and the three subspecies occur in Arctic and subarctic waters. ''S. elegans elegans'' is a coastal subspecies with oceanic influence. ''S. elegans arctica'' is a boreal-arctic form, and ''S. elegans baltica'' is the smallest form, found only in or near the Baltic Sea. All subspecies are typically found in waters 0-200m deep.Immerz, Antonia. Abundanz Und Verteilung Von Chaetognathen in Der Arktis. 25 July 2016, epic.awi.de/id/eprint/43249/1/BachelorThesis_AntoniaImmerz.pdf.

References

{{Taxonbar, from=Q2195676 Chaetognatha Planktology Animals described in 1873