Cordyceps is a genus of ascomycete fungi (sac fungi) that includes about 400 described species. All Cordyceps species are endoparasitoids, mainly on insects and other arthropods (they are thus entomopathogenic fungi); a few are parasitic on other fungi. The best known species of the genus is Cordyceps sinensis, first recorded as yartsa gunbu in Tibet in the 15th Century. It is known as yarsha gumba in Nepal. The Latin etymology describes cord as club, ceps as head, and sinensis as Chinese. Cordyceps sinensis, known in English commonly as caterpillar fungus, is considered a medicinal mushroom in oriental medicines, such as Traditional Chinese medicines and Traditional Tibetan medicine.
When a Cordyceps fungus attacks a host, the mycelium invades and eventually replaces the host tissue, while the elongated fruiting body (ascocarp) may be cylindrical, branched, or of complex shape. The ascocarp bears many small, flask-shaped perithecia contain the asci. These in turn contain the thread-like ascospores, which usually break into fragments and are presumably infective.
Some Cordyceps species are able to affect the behavior of their insect host: Cordyceps unilateralis causes ants to climb a plant and attach there before they die. This ensures the parasite's environment is at an optimal temperature and humidity and maximal distribution of the spores from the fruiting body that sprouts out of the dead insect is achieved. Marks have been found on fossilised leaves which suggest this ability to modify the host's behaviour evolved more than 48 million years ago.
The genus has a worldwide distribution and most of the approximately 400 species have been described from Asia (notably Nepal, China, Japan, Korea, Vietnam and Thailand). Cordyceps species are particularly abundant and diverse in humid temperate and tropical forests.
The genus has many anamorphs (asexual states), of which Beauveria (possibly including Beauveria bassiana, Metarhizium, and Isaria) are the better known, since these have been used in biological control of insect pests.
Some Cordyceps species are sources of biochemicals with interesting biological and pharmacological properties, like cordycepin; the anamorph of Cordyceps subsessilis (Tolypocladium inflatum) was the source of ciclosporin—a drug helpful in human organ transplants, as it suppresses the immune system (Immunosuppressive drug).
Leucochloridium Paradoxum, common name green-banded broodsac, is a parasitic flatworm (or "helminth") that uses gastropods as an intermediate host.
The worm in its larval, miracidia stage, travels into the digestive system of a snail to develop into the next stage, sporocyst. The sporocyst grows into long tubes to form swollen "broodsacs" filled with tens to hundreds of cercariae. These broodsacs invade the snail's tentacles (preferring the left, when available), causing a brilliant transformation of the tentacles into a swollen, pulsating, colorful display that mimics the appearance of a caterpillar or grub. The broodsacs seem to pulsate in response to light intensity, and in total darkness do not pulse at all. The infection of the tentacles of the eyes seems to inhibit the perception of light intensity. Whereas uninfected snails seek dark areas to prevent predation, infected snails have a deficit in light detection, and are more likely to become exposed to predators, such as birds. Birds are the definitive hosts where the cercariae develop into adult distomes in the digestive system of the bird. These adult forms sexually reproduce and lay eggs that are released from the host via the bird's excretory system. These droppings are then consumed by snails to complete the life cycle of this parasitic worm.
The resulting behavior of the flatworm is a case of aggressive mimicry, where the parasite vaguely resembles the food of the host. This gains the parasite entry into the host's body; this is unlike most other cases of aggressive mimicry, in which only a part of the host resembles the target's prey and the mimic itself then eats the duped animal.
This life cycle is similar to other species of genus Leucochloridium.
Intermediate hosts: Succinea putris – Hosts: birds, Zebra Finch (Taeniopygia guttata)
