By: Brian Jones, Owen Klassen, Sean Stoqua Chaetognatha By: Brian Jones, Owen Klassen, Sean Stoqua

Introduction Phylum Chaetognatha are often called ‘arrow worms’ Live in marine ecosystems Most are planktonic (80%) while some are benthic (20%) Most abundant type of animal present in many deep sea environments 120 modern species that range in size from 2 to 120 mm One of the earliest Bilaterians -but the name is actually derrived from latin, meaning “hair jaw” -planktonic – small organisms that float or drift in great numbers in fresh or salt water -benthic – meaning that they live near the floor of the sea -characterized by bilateral symmetry (they have a front and back end, as well as a topside and downside

Evolution While early fossils have been found .. Their fossils do not preserve well … Have been around since the Cambrian time period It has been hypothesized that they are linked to the deuterstome phyla or acanthocephalan worms Early fossils (300 million years) Deuterstome phyla – this view is based on certain embryological features that are shared between the two groups Acanthocephalan worms –based on the presence of an unusual cuticle structure

Characteristics Transparent or translucent torpedo shaped invertebrate Body is made up of three sections There is a fin on the tail as well as two sets of lateral fins They have a circulatory system, gaseous exchange organs or excretory system Hermaphroditic Gets its name from ‘grasping spines’ around its mouth Fins – tail fin is used for motion Lateral fins are used for stability An intestine runs the length of the trunk (where digestion occurs) ending in an anus just before the tail Hermaphroditic – carry both eggs and sperm Grasping spines – used to hunt, are covered up by a flexible hood (during swimming)

Interesting Facts Some have bioluminescent organs in their fins Some feed on freshly hatched fish and other arrow worms Contain neurotoxins used to paralyze and kill their prey They were around during the same time period of the dinosaurs Today they can be found in every ocean in the world

More Facts They are all carnivores Although they have been around for 300 million years, they are still abundant in numbers Considered a useful model for examining ancestral bilateran Their nervous system is relatively simple and resembles that of a protosome Also known as “glassworms”

Video https://www.youtube.com/watch?v=PkGhxtpK7IU The first 40 seconds of this video demonstrates the movements of the cool grasping spines of the chaetognatha

Sources http://academic.evergreen.edu/t/thuesene/chaetognaths/chaetognaths.htm http://www.helium.com/items/1291972-what-are-arrow-worms http://eol.org/pages/1740/overview http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Chaetognatha.html http://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/21862/1/23%282%29_P95-183.pdf