Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. Most measure between 0.5 and 1 mm long. Like flatworms they've a ciliated epidermis, but are unique in having but one cilium per cell. They've no body cavity, and no circulatory or respiratory system. Each gnathostomulid's simultaneously hermaphrodite, possessing an ovary and a testis. They're characterized by a specialized, muscular jaw, which they use to scrape smaller organisms off of the grains of sand t… (More on Gnathostomulid)