Animal Phyla/Chaetognatha


 * Chaetognatha
 * Name Meaning: Longhair jaw
 * English Common Name: Arrow worms
 * Major distinguishing characteristics: Chitinous spines either side of head, fins
 * Approximate number of species described: about 100 modern species

Natural History
Most species of Chaetognath are plaktonic. Some attached to algae or other substrate. They are hermaphroditic, having both male and female parts.

All species are predatory. They may rise and fall in the water column on a daily cycle.

Taxonomy
There is one class containing two orders.
 * Class Sagittoidea
 * Order Aphragmophora
 * Order Phragmophora

Anatomy
All species are transparent or translucent. They have three body parts, a head, trunk, and tail. The trunk has a pair of fins which help the animal move about in the water.

They have sharp hooks or spines on the head which allow them to grab prey.

They rise and fall in the water column using ammonia-filled vacuolated cells in the trunk.

The Fossil Record
Chaetognaths have been described as fossils of the early Cambrian Period, though that identification has been challenged. They almost certainly appear by the Pennsylvanian.

Quiz

 * /Chaetognatha Quiz/

References and Further Reading

 * Chaetognatha on Tree of Life
 * Chaetognatha on Encyclopedia of Life
 * Chaetognatha on Wikipedia