Chaetognatha is a phylum of predatory marine worms that are a major component of plankton worldwide. They show some preference for warmer waters. Chaetognaths are transparent and are torpedo shaped sometimes with arrowhead like opaque structures in their heads. They range in size from 3mm to 12cm. The common term for the phylum is Arrow Worms. There are about 100 modern species assigned to 15 genera. Despite the limited diversity, the number of individuals is staggering. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria (coral, jellyfish, anemones) Placozoa (trichoplax) Subregnum Bilateria (bilateral symmetry) Acoelomorpha (basal) Orthonectida (parasitic to flatworms, echinoderms, etc. ... Phyla Chaetognatha Echinodermata Hemichordata Chordata Deuterostomes (from the Greek: second the mouth) are one of the two superphyla of animals in the taxonomic branch bilateria, the other being the protostomes. ... Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Photomontage of plankton organisms For the Spongebob SquarePants character, see Sheldon J. Plankton. ...

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. Lynn Margulis and K. V. Schwartz place chaetognaths in the deuterostomes in their Five Kingdom classification.^[1] Molecular phylogenists, however, consider them to be protostomes. Thomas Cavalier-Smith places them in the protostomes in his Six Kingdom classification.^[2] 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 respiratory, circulatory, or excremental systems. Materials are moved about the body cavity by cilia. Waste materials are simply excreted through the skin. In botany the cuticle is the waxy covering produced by the epidermal cells of leaves to protect the plant from excessive water loss. ... Structure of chitin molecule In biology, chitin (pronounced keye-tin) is one of the main components in the cell walls of fungi, the exoskeletons of insects and other arthropods, and in some other animals. ... In zoology, a hermaphrodite is a species that contains both male and female sexual organs at some point during their lives. ... A human ovum An ovum (loosely, egg or egg cell) is a female sex cell or gamete. ... The signifier sperm can refer to: (mass noun, from Greek sperma = seed) a substance which consists of spermatozoa and which is a component of semen (mass noun) semen itself (informally, count noun with plural sperm or sperms) a single spermatozoon (= sperm cell) sperma ceti (Latin ceti, genitive of cetus = whale... A neurotoxin is a toxin that acts specifically on nerve cells, or neurons, usually by interacting with membrane proteins and ion channels. ... Phyla Chaetognatha Echinodermata Hemichordata Chordata Deuterostomes (from the Greek: second the mouth) are one of the two superphyla of animals in the taxonomic branch bilateria, the other being the protostomes. ... ... Lynn Margulis. ... In biology, phylogenetics (Greek: phylon = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e. ... Phyla Mollusca Arthropoda Annelida Protostomes (from the Greek: first the mouth) are a superphylum of animals in the taxonomic group bilateria, and include animals such as arthropods, mollusks, and nematodes. ... Thomas Cavalier-Smith is a professor of evolutionary biology at the University of Oxford, and is winner of the International Prize for Biology 2004 and one of the most notable researchers concerning the relationships, development, and classification of living things. ... Classes Adenophora    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The roundworms (Phylum Nematoda) are one of the most common phyla of animals, with over 20,000 different described species. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ...

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 Cambrian era. 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 Cambrian Maotianshan shales of Yunnan, China. Chaetognaths are thought possibly to be related to some of the animals grouped with the conodonts. The conodonts 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 conodonts. 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. The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... The Paleozoic Era is a major division of the geologic timescale, one of four geologic eras. ... The Burgess Shale (named after Mount Burgess, close to where the Shale was found) is a black shale exposure found high up in the Canadian Rockies in Yoho National Park near the town of Field, British Columbia. ... The Cambrian is a major division of the geologic timescale that begins about 542 Ma (million years ago) at the end of the Proterozoic eon and ended about 488. ... The 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. ... Conodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). ... Conodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ... Conodonts are extinct worm-like forms with distinctive conical or multi-denticulate teeth made of apatite (calcium phosphate). ... The Burgess Shale (named after Mount Burgess, close to where the Shale was found) is a black shale exposure found high up in the Canadian Rockies in Yoho National Park near the town of Field, British Columbia. ... Amiskwia is a small, probably gelatinous animal of unknown affinity known from fossils of the Middle Cambrian Burgess shale formation in British Columbia. ...

External links

• Friday chaetognath blogging - retrieved February 3
• Chaetognatha - retrieved February 3
• Invertebrates in the Plankton: Chaetognatha - retrieved February 3
• http://perezyvan.free.fr/Research/LeParco.htm Evolution and Development of Chaetognath - retrieved February 3
• Chaetognatha of the World - retrieved February 3
• ^ Systema Naturae 2000 Taxon: Phylum Chaetognatha per Margulis and Schwartz - retrieved February 3, 2006
• ^ Systema Naturae 2000 Taxon: Phylum Chaetognatha per Cavalier-Jones - retrieved February 3