Nematoida

Nematoida, also known as Nematomorpha or Gordiacea, are a phylum of parasitic worms also known as horsehair worms or Gordian worms. As larvae, they are parasitic on insects, including beetles, grasshoppers, crickets, and cockroaches, or other arthropods such as crustaceans and millipedes. The free-living adults are aquatic or semi-aquatic and can be found in streams, ponds, puddles, and damp soil.

Description:

Nematoid worms are typically long and thin, resembling strands of hair or thread. They are cylindrical in shape and range in color from light brown to black. Adults can range in length from a few centimeters to over a meter. They lack a functional digestive system as adults and rely on nutrients stored from their parasitic larval stage. They also lack a circulatory, respiratory, or excretory system.

Life Cycle:

The nematoid life cycle begins with the adult worms mating in water. Females lay eggs in gelatinous strings or masses. After hatching, the larvae must find a suitable host to continue their development. Larvae infect their hosts either through direct ingestion, penetration of the host's cuticle, or by encysting on vegetation that is then eaten by the host. Once inside the host, the larvae develop into juvenile worms, absorbing nutrients and growing. When the worm reaches maturity, it induces the host to seek out water, where the worm then emerges, often fatally injuring or killing the host. After emerging, the adult worm will reproduce and continue the cycle. Some species have been shown to manipulate the behavior of their hosts to increase the likelihood of the host encountering water.

Classification:

Nematoida are closely related to nematodes (roundworms), and both phyla are grouped together in the clade Nematoida. The exact phylogenetic relationships within Nematoida are still under investigation.

Ecological Significance:

Nematoida play a role in regulating insect populations. Their parasitic lifestyle can significantly impact the health and survival of their hosts.

Human Interaction:

Nematoida are not known to parasitize humans or cause any direct harm. However, their presence in water sources can sometimes be alarming due to their appearance.