Nematomorpha (sometimes called
Gordiacea, and commonly known as
Horsehair worms or
Gordian worms) are a
phylumIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
of parasitic
animalAnimals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously...
s that are
morphologicallyIn biology morphology is the form, structure and configuration of an organism.This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs...
and
ecologicallyEcology is the interdisciplinary scientific study of the interactions between organisms and the interactions of these organisms with their environment....
similar to
nematodeThe "roundworms" or "nematodes" are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 80,000 have been described, of which over 15,000 are parasitic. It has been estimated that the total number of...
worms, hence the name. They range in size from 1 cm to 1 meter long, and 1 to 3 millimetres in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the
larvaA larva is a young form of animal with indirect development, going through or undergoing metamorphosis ....
e are parasitic on
beetleBeetles are the group of insects with the largest number of known species. They are classified in the order Coleoptera , which contains more described species than in any other order in the animal kingdom, constituting about 25% of all known life-forms...
s,
cockroachCockroaches are insects of the order Blattaria. This name derives from the Latin name for the insect, Blatta....
es,
OrthopteraThe Orthoptera are an order of insects with paurometabolous or incomplete metamorphosis, including the grasshoppers, crickets and locusts.Many insects in this order produce sound by rubbing their wings against each other or their legs, the wings or legs containing rows of corrugated bumps...
and
crustaceanCrustaceans are a very large group of arthropods, comprising almost 52,000 described species , and are usually treated as a subphylum . They include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles...
s. About 326 species are known and a conservative estimate suggests that there may be about 2000 species worldwide. The name "Gordian" stems from the legendary
Gordian knotThe Gordian Knot is a legend associated with Alexander the Great. It is often used as a metaphor for an intractable problem, solved by a bold stroke :"Turn him to any cause of policy,
...
. This relates to the fact that nematomorpha often tie themselves in knots.
Description and biology
Nematomorphs possess an external
cuticleA cuticle , or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Cuticles are non-homologous, differing in their origin, structure and chemical composition.-Human anatomy:In human anatomy, cuticle ...
without cilia. Internally, they have only longitudinal muscle and a non-functional gut, with no
excretoryThe excretory system is a biological system that removes excess, unnecessary or dangerous materials from an organism. It is responsible for the elimination of oxygen waste products of metabolism as well as other nitrogeneous materials. Since the normal operation of most biological systems creates...
,
respiratoryThe respiratory systems function is to allow gas exchange to all parts of the body. The space between the alveoli & the capillaries, the anatomy or structure of the exchange system, and the precise physiological uses of the exchanged gases vary depending on the organism...
or
circulatory system- [Headline text]--75.137.171.242 01:21, 21 October 2009 :bThe circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, nitrogen waste products, etc. to and from cells in the body to help fight diseases and help stabilize body temperature and pHb to maintain...
s. Reproductively, they are
dioeciousDioecious species are whose members can produce only one type of gamete; each individual organism belonging to a dioecious species is distinctly male or female . The majority of animal species are dioecious...
, with the internal fertilization of eggs that are then laid in gelatinous strings. The larvae that hatch have rings of cuticular hooks and terminal stylets that are believed to be used to enter the hosts. They are mostly free living but males and females aggregate into tight balls (
Gordian knots) during mating.
In
Spinochordodes telliniiThe nematomorph hairworm Spinochordodes tellinii is a parasitic worm whose larvae develop in Orthopteran insects . This parasite is able to influence its host's behavior: once the parasite is grown, it causes its grasshopper host to jump into water, where the grasshopper will likely drown...
, which has orthopterans as its vector, the infection acts on the insect's brain and causes it to seek water and drown itself, thus returning the nematomorph to water. They are also remarkably able to survive the predation of their host, being able to wriggle out of the predator that has eaten the host.
Taxonomy
Nematomorphs can be confused with nematodes, particularly
MermithidMermithidae is a family of nematode worms that are endoparasites in arthropods. As early as 1877, Mermithidae was listed as one of nine subdivisions of the Nematoidea. Mermithidae are confusable with the horsehair worms of the phylum Nematomorpha that have a similar life history and...
worms. Unlike Nematomorphs, Mermithids do not have a terminal
cloacaIn zoological anatomy, a cloaca is the posterior opening that serves as the only such opening for the intestinal, reproductive and urinary tracts of certain animal species. The word comes from Latin, and means sewer...
. Male mermithids have one or two spicules just before the end apart from having a thinner, smoother cuticle, without areoles and a paler brown colour.
The phylum is placed along with the
EcdysozoaThe Ecdysozoa are a grouping of protostome animals, including the Arthropoda , Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes...
clade of moulting organisms that include the
ArthropodAn arthropod is an invertebrate that has an exoskeleton , a segmented body, and jointed attachments called appendages. Arthropods are animals belonging to the Phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
a. Fossilized worms have been reported from Early Cretaceous Burmese amber dated to 100–110 million years apart from a fossil from the Mesozoic.
Relationships within the phylum are still somewhat unclear, but two classes are recognised:
- Class Nectonematoida: Marine, planktonic, with a double row of natotory seta
Seta is a biological term derived from the Latin word for "bristle". It refers to a number of different bristle- or hair-like structures on living organisms.-Animal setae:In zoology, most "setae" occur in invertebrates....
e along each side of the body; with dorsal and ventral longitudinal epidermal cords, blastocoelom spacious and fluid filled; gonadThe gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s single; larvae parasitise decapod crustaceansThe decapods or Decapoda are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers.-Anatomy:...
- Class Gordioidea: Freshwater and semiterrestrial; lack lateral rows of setae; with a single, ventral epidermal cord; blastocoelom filled with mesenchyme
Mesenchyme, or mesenchymal connective tissue, is an example of reticular connective tissue, a type of loose connective tissue, which is derived from all three germ layers and located within the embryo . Mesenchyme is characterized morphologically by a prominent ground substance matrix containing a...
in young animals but becomes spacious in older individuals; larvae primarily parasitise Orthoptera
External links
- Nematomorpha Biodiversity Project website. Provides pictures, life cycle information and searchable databases.
- horsehair worms on the UF
The University of Florida is a public land-grant, sea-grant, space-grant major research university located on a campus located in Gainesville, Florida, in the United States. The university traces its origins to 1853, and has continuously operated on its present Gainesville campus since the fall...
/ IFASThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
Featured Creatures Web site
Videos
- Videos of a cricket infected with a Gordian worm with the worm emerging to mate, as well as emerging from predators that have eaten the infected cricket. From Nature
Nature is a prominent British scientific journal, first published on 4 November 1869. Most scientific journals are now highly specialized, and Nature is among the few journals that still publish original research articles across a wide range of scientific...
, April 2006. — explains the proteomeThe proteome is the entire complement of proteins expressed by a genome, cell, tissue or organism. More specifically, it is the set of expressed proteins at a given time under defined conditions. The term is a portmanteau of proteins and genome....
research done on this worm
- The cricket suicide (video)