Nectonema

Nectonema is a genus of parasitic nematomorph worms belonging to the class Nectonematoida. These worms are unique among nematomorphs due to their exclusively marine habitat. They are parasites of decapod crustaceans, particularly crabs and shrimp.

Description: Nectonema adults are free-living in the ocean and can be quite long, slender, and translucent. They lack a digestive system, absorbing nutrients through their body wall. A defining characteristic is the presence of two rows of natatory bristles along each side of the body, used for swimming. These bristles are not found in other nematomorph groups. The anterior end of the worm possesses a crown of cephalic bristles.

Life Cycle: The life cycle begins with the adult Nectonema spawning in the ocean. The larvae are thought to infect crustacean hosts, likely through ingestion. Inside the host, the larva develops into a juvenile worm, absorbing nutrients and growing. Once the worm reaches maturity, it emerges from the host, often causing the host's death. The adult worm then lives freely in the ocean, reproduces, and restarts the cycle.

Taxonomy: Nectonema is the only genus in the family Nectonematidae and the order Nectonematoida. This group is considered relatively ancient and distinct from other nematomorphs, which are typically freshwater or terrestrial parasites of insects. The exact phylogenetic relationships within the nematomorphs are still under investigation.

Distribution: Nectonema species are found in marine environments worldwide.

Ecological Significance: Nectonema plays a role in marine ecosystems as a parasite, influencing the populations of its crustacean hosts. Its presence and abundance can be indicators of environmental health and ecosystem stability. Its unique adaptations to a marine parasitic lifestyle make it a subject of interest in evolutionary biology.