Nematodes within the Secernentea have phasmids, which are unicellular glands. Phasmids likely function as chemoreceptors. Females may produce pheromones to attract males.
Nematodes in general have papillae, setae and amphids as the main sense organs. Setae detect motion (mechanoreceptors), while amphids detect chemicals (chemoreceptors).
Communication Channels: tactile ; chemical
Other Communication Modes: pheromones
Perception Channels: tactile ; chemical
The life cycle of Dracunculus insignis is fairly simple and involves at least two hosts. Females carrying larvae internally release a toxin which causes the formation of a blister on the hosts skin. This blister bursts open on contact with water allowing the female to release her larvae upon contact with water. Dracunculus insignis passes through two larval stages in an intermediate copepod host, either Cyclops vernalis or C. bicuspidatus thomasi. After penetrating the intermediate host, larvae migrate to the hemocoel within one to two hours. Growth is temperature dependent. Temperatures between 8 and 15°C showed no development of larvae after sixty days. At 24°C the first molt occurs after just eight or nine days. A second molt follows just seven days later. At the third larval stage, D. insignis exits the host through the skin and must be in water. The larvae must be swallowed either by a paratenic host or the definitive host. Frogs often serve as paratenic hosts and Dracunculus insignis must wait for a definitive host to eat the frog. Definitive hosts for D. insignis are North American carnivores which are usually semi-aquatic. These include, mink, raccoon, otter, fisher, and occasionally domestic dogs. Upon reaching the definitive host, D. insignis undergoes two molts before reaching adulthood. The molt to the fourth stage takes place after one to two weeks after being ingested by the definitive host. Males will have completed the final molt to adulthood after approximately sixty days while females mature in sixty-five to seventy days. By 120 to 270 days, most females will have been fertilized and have their uterus full of larvae.
Dracunculus insignis does not parasitize humans. However, it does infect carnivores, including domestic dogs. A dog parasitized by D. insignis will exhibit subcutaneous swellings between three and five cm in diameter. Most often these can be found on the limbs, but they have been reported on the head of dogs. Dehydration, vomiting, diarrhea, and asthma are also common symptoms of infection. Infestation usually involves a trip to the veterinarian for removal of the parasite. The procedure for removing D. insignis involves placing the dog in water deep enough to cover the wounds thus causing the adult females to emerge from the swellings. This is followed by dissection to completely remove the parasites.
A close relative of Dracunculus insignis, D. medinensis (the Guinea worm) is responsible for a condition known as dracunculiasis in humans throughout much of Africa and the Middle East. Chemicals to kill the parasite are being tested on D. insignis in hopes of eradicating the problems caused by D. medinensis.
Negative Impacts: causes or carries domestic animal disease
The life cycle of Dracunculus insignis involves at least two hosts: an intermediate copepod host, either Cyclops vernalis or Cyclops bicuspidatus thomasi. Definitive hosts for D. insignis are North American carnivores which are usually semi-aquatic. These include, mink, raccoon, otter, fisher, and occasionally domestic dogs.
Ecosystem Impact: parasite
Species Used as Host:
Dracunculus insignis is an endoparasite with individuals being found most often in the intramuscular connective tissue of the limbs as well as the subcutaneous tissue of the abdomen in the definitive host. The diet of both juveniles and adult females is composed of host tissue fluid and a small amount of blood. Pharyngeal glands and intestinal epithelium produce digestive enzymes. Extracellular digestion begins within the lumen and is finished intracellularly. Adult males, with their atrophied gut, do not feed.
Animal Foods: blood; body fluids
Primary Diet: carnivore (Eats body fluids)
Dracunculus insignis is limited to North America.
Biogeographic Regions: nearctic (Native )
While outside of a host, Dracunculus insignis is limited to aquatic environments. As such, D. insignis requires a semi-aquatic or fully aquatic host such as a mink, raccoon, otter, fisher, and occasionally domestic dogs.
Habitat Regions: temperate ; tropical
Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; rainforest ; scrub forest ; mountains
Aquatic Biomes: lakes and ponds; rivers and streams; temporary pools
Wetlands: marsh ; swamp ; bog
Other Habitat Features: urban ; suburban ; agricultural ; riparian
Dracunculus insignis adults are white cylindrical worms 17.6 to 23.0 cm in length and 3 to 4 mm at maximum width. Dracunculus insignis is dioecious. Females are much larger than males when they are filled with first-stage larvae. Larvae are approximately 500 microns long and 50 microns wide. Over the course of development, the head changes from a pointed shape to a dome shape by adulthood.
The worm's cuticle has three or more main outer layers made of collagen and other compounds. The outer layers are non-cellular and are secreted by the epidermis. The cuticle layer protects the nematodes so they can invade the digestive tracts of animals. The worms molt four times, the first two before hatching, and then before their adult stage.
Longitudinal muscles are along the body wall and are obliquely arranged in bands. Dorsal, ventral and longitudinal nerve cords are connected to the main body of the muscle.
The mouth leads to a thin esophagus and intestine. The male intestine is completely atrophied. As a nematode in the group Secernentea, these worms have a specialized tubular excretory system with three canals. The canals are arranged to form an “H”.The rectum is long and tubular in shape.
Range length: 17.6 to 23 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: female larger; sexes shaped differently
These parasites are usually not preyed on directly, but are ingested from host to host.
Females may produce a phermomone to attract males. The male coils around a female with his curved area over the female genital pore. The gubernaculum, made of cuticle tissue, guides spicules which extend through the cloaca and anus. Mating occurs when a male inserts a spicule into the female's vulva and releases his sperm. Males use spicules to hold the female during copulation. Nematode sperm are amoeboid-like and lack flagella. The fertilized eggs develop into larvae within the uterus. By 120 to 270 days, most females will have been fertilized and have their uterus full of larvae. Females will create a lesion in their host from which they will send their larvae into the water by 300 to 365 days post-infection. Females release eggs for five to seven days after which they die and are absorbed into the host body. The rare occurrence of Dracunculus insignis males is due to their death directly following mating.
Key Reproductive Features: sexual ; fertilization (External ); ovoviviparous
Parental Investment: pre-fertilization (Provisioning)
