Eusirus holmi is a large marine amphipod, reaching a maximum length of 4 cm. Its body is mainly white in colour, however individuals also host reddish-brown and orange highlights. The eyes are intermediate in size and red in colour. The species possessantennae, which are as long as its body. Individuals also possess well developed graspingclaws on their first two pairs of legs. The species is predatory, using these grasping claws to capture and hold on to prey. After breeding E. holmi lays several hundred eggs into a brood pouch, with eggs hatching during the warmersummer months.