Capitella capitata is a polychaete worm that grows up to 10 cm in length.

It may be found under pebbles or small stones, with the burrows at or near the surface of the sediment.

It is an opportunistic species tolerant of stressful conditions, and often found in polluted waters (sewer discharges, hydrocarbons, metals ...) where it out-competes less tolerant species.

[1] Capitella capitata is able to vary its reproductive strategy in accordance with its current environmental conditions.

In contrast, C. capitata can produce planktonic larvae if there is a need to discover new habitats.