Chaetognatha
Methods

Any plankton net may be used to collect planktonic chaetognaths, with mesh size varying according to the size of species sought. For species living in newly described habitats, however, special gear is needed. Samples a few metres above the bottom can be obtained with mid water trawls, nets fixed on submersibles, and bottom sledges provided with nets. With these methods, about twenty new deep species and two new genera of bentho-planktonic chaetognaths (family Heterokrohniidae) have been discovered recently. In very shallow waters, bentho-planktonic species living among seagrass meadows may be caught with towed epibenthic sledges, or in plankton traps. A recently newly discovered habitat for chaetognaths, dark submarine caves, is investigated with traps baited with pieces of various invertebrates. Until now, only two benthic species (spadellids) have been discovered, but bentho-planktonic ones may also exist.

Specimens are well preserved in 4% formalin. Alcohol must be avoided to prevent shrinkage. Colouring with methylene blue is useful for distinction and identification of related species. Indeed, it permits observation of body parts that are hardly visible in nature, such as corona ciliata, limits of the lateral fins, or extensions of rays on fins.