Calispadella alata n. gen., n. sp., the first chaetognath recorded from a hydrothermal vent site (Mid-Atlantic Ridge)

Calispadella alata n. gen., n. sp., is the first chaetognathdescribed from a hydrothermal vent field (Mid-Atlantic Ridge,depth 1600 m). It belongs to the family Spadellidae (presenceof transverse muscles in trunk and long tail segment). Thereis a pair of lateral fins making no contact with the body posteriorly;these free wing-like extensions end in festoons provided distallywith patches of adhesive cells. This unique feature in a deepbentho-planktonic species can be seen as an adaptation to adhereat times to the substrate to resist local turbulences producedby the hydrothermal fluids. This may also indicate that thisnew genus is phylogenetically close to the neritic genus Paraspadella,which has adhesive finger-like processes. Calispadella alatais sexually precocious as reported for other deep chaetognaths,contrary to most deep living organisms which exhibit delayedsexual maturity. This feature might be a means to increase thepossibility of mating in scarce populations.