Nephtyidae is a taxonomic family of worms. They are commonly referred to as catworms.
Nephtyidae are pale, clearly segmented polychaetes with a small pentagonal prostomium with two pairs of small antennae. There segments are little differentiated and have a rectangular cross-section.
Nephtyids are active predators, with a strong muscular proboscis, armed with two well developed jaws.
They can dig relatively fast through sandy sediments. They can also swim with sinuous movements.