Chaetognatha

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Chaetognatha

(kētôgnăth`ə), phylum of predominantly pelagic marine animals commonly known as arrowworms. Arrowworms have slender, transparent bodies, usually under 1 in. (2.5 cm) long. Lateral and caudal fins propel the animal in sudden darting movements. The well-developed head bears eyes and other sense organs, grasping spines used in the capture of prey, and rows of teeth flanking the mouth. A protective hood can be folded down over the bristles and teeth. The digestive system includes a glandular pharynx, a straight intestine, and a short, muscular rectum. The nervous system centers in a bilobed, dorsal brain and several other nerve ganglia. Although widely distributed, arrowworms prefer warm, shallow seas and are particularly plentiful in the Indo-Pacific region. They are voracious predators; some feed on freshly hatched fish nearly as large as themselves. They are influential planktonic consumers when abundant.
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Chaetognatha

A phylum of abundant planktonic arrow-worms. Their bodies are tubular and transparent, and divided into three portions: head, trunk, and tail. The head possesses one or two rows of minute teeth anterior to the mouth and usually 7–10 larger chaetae, or seizing jaws, on each side of the head. One or two pairs of lateral fins and a caudal fin are present.

Nine genera and about 42 species are recognized by some specialists. Most species belong to the genus Sagitta, which can be recognized by the presence of two pairs of teeth and two pairs of lateral fins.

Chaetognaths are cosmopolitan forms which live not only at the surface but also at great depths; however, no one species is found in all latitudes and at all depths. One of the Arctic species, Eukrohnia hamata, may extend to the Antarctic by way of deep water across the tropics. A few species are neritic and are not found normally beyond the continental shelf. Their food consists principally of copepods and other small planktonic crustaceans; however, they are very predacious and will even eat small fish larvae and other chaetognaths on rare occasions.

Studies have shown them to be useful as indicator organisms. Certain species appear to be associated with characteristic types or masses of water, and when this water is displaced into an adjacent water mass, the chaetognaths may be used as temporary evidence for such displacement.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Chaetognatha

 

(arrowworms), a phylum of marine invertebrates having a transparent elongate body that measures 5 mm to 9 cm in length. There are lateral fins and a caudal fin. The head bears sickle-shaped bristles that serve to capture prey. The coelom is divided by transverse septa into a head, trunk, and tail. The digestive tract is straight. There are no circulatory or excretory systems. The nervous system consists of an epipharyngeal brain and a ventral ganglion that are connected by long longitudinal cords. Chaetognaths are hermaphrodites. They are predators that live amid marine plankton. There are six genera, embracing about 30 species. Chaetognaths are usually assigned to the group of deuterostome animals; sometimes the invertebrates are regarded as an independent taxonomic category higher than a phylum.

REFERENCES

Filatova, Z. A. “Klass shchetinkocheliustnykh.” In Rukovodstvo po zoologii, vol. 3, part 2. Moscow, 1951.
Beklemishev, V. N. Osnovy sravnitel’noi anatomii bespozvonochnykh, 3rd ed., vols. 1–2. Moscow, 1964.
Dogel’, V. A. Zoologiia bespozvonochnykh, 6th ed. Moscow, 1975.

A. V. IVANOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

Chaetognatha

[‚kē′täg·nə·thə]
(invertebrate zoology)
A phylum of abundant planktonic arrowworms.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
2A1, D, F) suggest that they grew similarly to the grasping spines of chaetognaths, by basal accretion of thin laminae (Szaniawski 2002).
Localized disturbances of hexagonal packing of epithelia cells, whereby other polygons become interspersed with hexagons, is not uncommon (Gibson et al., 2006), and this is seen in both species of bioluminescent chaetognath. We know of no other bioluminescent organism that has evolved a hexagonal packing system to contain bioluminescent materials.
They are reported as an important food-link and as common prey for chaetognaths and fish larvae (Feigenbaum and Maris 1984).
Their diet comprised seven major prey groups (copepods, chaetognaths, amphipods, euphausiids, ostracods, unidentified fish, and unidentified gelatinous prey) and was dominated by copepods and chaetognaths.
Chaetognath assemblages in the Mexican Caribbean Sea (1991).
* Group B: Sub-Antarctic species represented by the pteropod Limacina retroversa and the chaetognath Sagitta tasmanica.
1873 discarded houses), chaetognaths Miraciinae Dana, 1846 Trichodesmium Ehrenberg ex (Distioculus Huys and Gomont, 1892 Bottger-Schnack, 1994, Macrosetella Scott, 1909, Mirada Dana, 1846, Oculosetella Dahl.
Plankton samples were comprised of primarily crustaceans (copepods, amphipods, euphausiids, and decapod (brachyuran, pagurid, caridean) larvae) and chaetognaths with some polychaetes, gastropods, cnidarians, echinoderm larvae, and fish larvae and eggs; no red, blue, or golden king crab larvae were present.
They seek plankton patches dominated by tiny crustaceans--shrimp, copepods--and predatory worms called chaetognaths.
The tendency observed in the North Atlantic is repeated in other oceans, although in the tropical areas of the Pacific and Indian oceans the biomass of krill is greater, and in addition, other groups, such as amphipods, chaetognaths, cnidarians, and pteropod mollusks each represent about 5% of the total biomass.