Gnathostomulids

Gnathostomulids are a phylum of marine invertebrate animals that are part of the larger group of bilaterian animals. They are characterized by their lack of a rigid exoskeleton and are often described as "threadworms" or "horsehair worms" due to their elongated and thin bodies, which can range in length from millimeters to centimeters. Gnathostomulids have a simple, open circulatory system and are able to move about using a type of motion called "irroriculture," by waving a thin, hair-like structure along the entire length of their body.

Gnathostomulids are typically found in marine environments, ranging from shallow tide pools to deeper ocean waters. They are reported to be abundant in certain areas, but are often overlooked due to their small size and intricate habitat requirements. In terms of behavior, gnathostomulids are predators and feed on small invertebrates and detritus. Some species have even been observed actively hunting down prey.

The systematic classification of gnathostomulids is still a subject of ongoing research and some taxonomic groups are considered to be paraphyletic or polyphyletic. They are generally considered to be closely related to other small, body-hair-like invertebrates such as rotifers and some species of parasitic wasps.

In popular culture, gnathostomulids have gained some attention due to their unique appearance and predacious behavior, however, scientific understanding and description of these organisms is quite limited. Little research is conducted on these organisms, which are thought to be extremely diverse in their morphology and as such, more thorough investigations in this field are necessary to increase our knowledge about gnathostomulids.