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 ^[1]. They almost certainly appear by the Pennsylvanian.

Quiz

Chaetognatha Quiz

References and Further Reading

↑ Morris, Simon Conway. 2009. The Burgess Shale Animal Oesia is not a Chaetognath: A Reply to Szaniawski (2005). Acta Palaeontologica Polonica 54(1):175-179.

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

[1] Morris, Simon Conway. 2009. The Burgess Shale Animal Oesia is not a Chaetognath: A Reply to Szaniawski (2005). Acta Palaeontologica Polonica 54(1):175-179.

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