any of certain marine crustaceans of the family Caprellidae (order Amphipoda), particularly of the genera Caprella and Aeginella. The common name derives from the slender body structure. Most species are predators on other small animals, but some feed on organic debris.

Aeginella longicornis (longicornia), which occurs among eelgrass, sponges, and wharf pilings between Labrador and the mid-Atlantic coast of the United States, is about 2.5 centimetres (1 inch) long and muddy green or brown in colour. Like most other skeleton shrimp, it moves with a high-arching action similar to that of the measuring worm.

Caprella septentrionalis, with habits similar to those of A. longicornis, is found in the North Sea and on the North American coast from Greenland to New England; it attains a length of 3.2 centimetres (1.3 inches). C. grahami lives between the tubefeet of the common starfish Asterias forbesi and feeds on organic matter adhering to mucus secreted by the starfish.