Pentastomida
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Tongueworm is any of a group of parasitic, wormlike animals found in the respiratory system of vertebrates, especially reptiles. Tongueworms cling to the lining of the nasal passageways and lungs where they feed on the blood of the host. Also called pentastomids, tongueworms occur worldwide, although most species are tropical.
The body of the tongueworm is highly modified for parasitism, that is, obtaining nourishment from the body of another, usually larger host organism (see Parasite). Adults of most species are 2 to 13 cm (0.8 to 5.1 in) long. Their mouth is jawless and sometimes projects outward as a trunklike proboscis. The mouth is flanked by two pairs of small, fingerlike projections equipped with claws that are used to attach to the host. The name pentastomid, meaning five-mouthed, derives from the fact that, in some species, these four grasping organs resemble the proboscis and look like additional mouths. The single, true mouth leads to a long, straight gut, the front of which forms a muscular pharynx for sucking blood. Frontal glands near the mouth of the tongueworm produce substances that break down the host tissue or prevent the host's blood from clotting. Like most internal parasites, tongueworms have no organs of excretion, gas exchange (breathing), or circulation. The tongueworm's blood flows freely throughout the body cavity. The tongueworm's nervous system consists of a frontal ganglion, or primitive brain, and a ventral nerve cord that runs along the bottom of the body cavity.
The sexes of tongueworms are separate, and the females are larger than the males. Fertilization is internal and occurs within the primary host. The larva has two or three pairs of walking legs, each with two claws. The larva may be autoinfective, that is, it remains in the primary host. If not autoinfective, the larva may form a protective capsule, called a cyst, which either moves through the digestive tract to be deposited with the host's feces or moves passively out of the host's nose or mouth.
Tongueworm eggs may pass out of the host before they hatch. If an intermediate host animal accidentally swallows the cyst or egg, the infective larva emerges inside the new host. It bores through the gut wall and completes its development into the next infective stage. If the intermediate host is eaten by a predator, the predator may acquire the pre-adult tongueworm. The juvenile tongueworm then crawls up the esophagus to the respiratory system and implants itself in the lungs or nasal passageways to complete the cycle. The larvae of one species of tongueworm that infests reindeer can infest the next generation of hosts by boring through the placenta. Examples of typical intermediate hosts and their corresponding primary hosts are cockroaches and lizards, fish and crocodiles, and rabbits and dogs.
Scientific classification: Tongueworms make up the phylum Pentastomida. Their relationship to other animals is not clear; they resemble both arthropods and annelids. One theory on the origin of this group is that they are actually highly modified crustaceans.
Tongueworm is any of a group of parasitic, wormlike animals found in the respiratory system of vertebrates, especially reptiles. Tongueworms cling to the lining of the nasal passageways and lungs where they feed on the blood of the host. Also called pentastomids, tongueworms occur worldwide, although most species are tropical.
The body of the tongueworm is highly modified for parasitism, that is, obtaining nourishment from the body of another, usually larger host organism (see Parasite). Adults of most species are 2 to 13 cm (0.8 to 5.1 in) long. Their mouth is jawless and sometimes projects outward as a trunklike proboscis. The mouth is flanked by two pairs of small, fingerlike projections equipped with claws that are used to attach to the host. The name pentastomid, meaning five-mouthed, derives from the fact that, in some species, these four grasping organs resemble the proboscis and look like additional mouths. The single, true mouth leads to a long, straight gut, the front of which forms a muscular pharynx for sucking blood. Frontal glands near the mouth of the tongueworm produce substances that break down the host tissue or prevent the host's blood from clotting. Like most internal parasites, tongueworms have no organs of excretion, gas exchange (breathing), or circulation. The tongueworm's blood flows freely throughout the body cavity. The tongueworm's nervous system consists of a frontal ganglion, or primitive brain, and a ventral nerve cord that runs along the bottom of the body cavity.
The sexes of tongueworms are separate, and the females are larger than the males. Fertilization is internal and occurs within the primary host. The larva has two or three pairs of walking legs, each with two claws. The larva may be autoinfective, that is, it remains in the primary host. If not autoinfective, the larva may form a protective capsule, called a cyst, which either moves through the digestive tract to be deposited with the host's feces or moves passively out of the host's nose or mouth.
Tongueworm eggs may pass out of the host before they hatch. If an intermediate host animal accidentally swallows the cyst or egg, the infective larva emerges inside the new host. It bores through the gut wall and completes its development into the next infective stage. If the intermediate host is eaten by a predator, the predator may acquire the pre-adult tongueworm. The juvenile tongueworm then crawls up the esophagus to the respiratory system and implants itself in the lungs or nasal passageways to complete the cycle. The larvae of one species of tongueworm that infests reindeer can infest the next generation of hosts by boring through the placenta. Examples of typical intermediate hosts and their corresponding primary hosts are cockroaches and lizards, fish and crocodiles, and rabbits and dogs.
Scientific classification: Tongueworms make up the phylum Pentastomida. Their relationship to other animals is not clear; they resemble both arthropods and annelids. One theory on the origin of this group is that they are actually highly modified crustaceans.
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