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Chatognaths are transparent or translucent and are covered by a cuticle. They have fins and a pair of hooked, chitinous, grasping spines on each side of their heads that are used in hunting. The spines are covered with a hood when swimming. They have a distinct head, trunk and tail. All species are hermaphroditic, carrying both eggs and sperm. A few species are known to use neurotoxins to subdue prey. Chaetognaths are traditionally classed as deuterostomes by embryologists. Molecular phylogenist s, however, consider them to be protostomes. They have some developmental similarities to nematodes. Although they have a mouth with one or two rows of tiny teeth, compound eyes, and a nervous system, they have no repiratory, circulatory, or excremental systems. Materials are moved about the body cavity by cilia. Waste materials are simply excreted through the skin.

Chaetognaths swim using their tail fin for propulsion and the body fins for stabilization and steering.

Chaetognaths fossilize poorly, but are thought to have originated in the CambrianThe Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period. It is the first peri. Chaetognath grasping spines are found occasionally as fossils from the late Paleozoic onward. Complete body fossils that have not been formally described are reported from the Kicking Horse Shale member of the Middle Cambrian Burgess Shale of British Columbia and the Lower CambrianThe Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period. It is the first peri Maotianshan shalesThe Maotianshan shale is an early Cambrian rock formation exposed in the Yunnan Province of China in the villages of Ercaicun and Chengjiang near the city of Kunming. These shales appear very early in the Cambrian sequence in China. They were discovered a of Yunnan, China. Chaetognaths are thought possibly to be related to some of the animals grouped with the conodontsConodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). The animals are sometimes referred to as conodontophora ("bearers of conodonts"), taking the word "conodont" to refer to the tee. The conodontsConodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). The animals are sometimes referred to as conodontophora ("bearers of conodonts"), taking the word "conodont" to refer to the tee themselves, however, are thought to be related to the vertebrates. It is now thought that the protoconodonts , which are known only from their teeth, might be chaetognaths rather than conodontsConodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). The animals are sometimes referred to as conodontophora ("bearers of conodonts"), taking the word "conodont" to refer to the tee. The Burgess Shale fossil Amiskwia is thought by some to be a Chaetognath, but it lacks teeth and is generally thought to belong to some other phylum of worms.