Key to some common neritic chaetognaths of California, Oregon and Washington.

Prepared by Erik V. Thuesen

1. Heavy transverse musculature along the body segment gives opaque appearance, small (< 10 mm), one pair of lateral fins, benthic or epibenthic, often attached to algae or other substrate: Family Spadellidae >>> 2

  • No transverse musculature along the body segment, transparent, size can exceed 20 mm, two pairs of lateral fins, planktonic: Family Sagittidae >>> 3

    • 2. Without adhesive organs, body length to 6.5 mm >>> Spadella bradshawi. 

  • With adhesive organs, body length to 3.8 mm >>> Paraspadella pimukatharos.

    • 3. Inner edges of grasping spines with small serrations (400x), seminal vesicles with anterior nipple, matures at 14-17 mm >>> Serratosagitta bierii. 

  • Grasping spines without serrations, no anterior nipple on seminal vesicles >>> 4

    • 4. Fins with complete rays >>> 5

  • Fin rays very sparse and/or only filling outer edges >>> 6

    • 5. Two rows of eggs in each ovary extend as far as, or further than, the middle of the anterior fins, collarette extensive, seminal vesicles with terminal knobs when fully mature, body length to 26 mm >>> Sagitta bipunctata.

  • Ovaries do not reach the anterior fins >>> 7

    • 6. Ovaries may extend past the leading edge of the posterior fins; sperm usually forms a heavy "V" pattern in the tail section, whereby the anterior and central portion of the tail section is devoid of sperm, seminal vesicles are simple bulbs, total body length when mature is more than 15 mm >>> Flaccisagitta enflata.

  • Ovaries shorter than the length of the posterior fins with a few large ova, highly transparent with buoyancy sac mesenteries often visible, Seminal vesicles are very simple, total mature body length less than 10 mm >>> Mesosagitta minima.

    • 7. Anterior fins, seminal vesicles and posterior fins may all be touching in alignment, collarette-type tissue extends the length of the body, mature body length of 8-16 mm >>> Parasagitta euneritica.

  • Posterior fins not touching seminal vesicles, mature body length of 24-48 mm >>> Parasagitta elegans.