Armandia brevis is an undulatory burrowing opheliid polychaete found in surficial heterogeneous sediments (muds) (Dorgan et al., 2013). Its fast, energetic undulatory behavior is superficially similar to undulatory behavior exhibited by nematodes. A. brevis also exhibits swimming behavior, particularly during the spawning phase of its life cycle.
A. brevis has a smooth, rigid body with ventral and lateral grooves extending along the entire elongated body. Internally, A. brevis has longitudinal and oblique muscles, but lacks circular muscles (Clark and Hermans, 1976; Law et al., 2014).