This alien-like creature belongs to the family of skeleton-shrimps or ghost shrimps. Their common names denotes the threadlike slender body which allows them to virtually disappear among the fine filaments of seaweed, hydroidsand bryozoans. The family includes approximately 170 species, all easily recognizable from other amphipodsbecause of their slender elongated bodies. They are all exclusively marine and are found in oceans worldwide. Caprella septentrionalis lives in the Arctic and Northern Atlantic.
The species reaches a length of 3 cm, where males are larger than females. Mating can only occur moments after the female has molted. Males locate potential partners with the aid of their antenna to detect the pheromones released by the females; the male then rides or carries the female until the latter is ready to molt.