Description: This caprellid grows up to 23 mm and has a smooth body and head, with some small tubercles occasionally present towards the rear. The rostrum is not clearly differentiated from the head. The 3rd segment on antenna 1 is more than half the length of the 2nd segment. There are swimming setae (hairs) on antenna 2. The first set of gnathopods have 2 grasping spines. The 2nd set of gnathopods have strong forward-facing spines on each side, and single grasping spines along with a large rectangular tooth and some smaller teeth. Pereopods 2 and 3 are absent, or very poorly developed. Pereopod 5 is well developed, with 7 articles.

Habitat: Sublittoral, usually on buoys or floats.

Distribution: A few scattered records around Britain and Ireland, mostly in the south. Has been recorded as far north as Shetland. Type locality is in United States, and it has a cosmopolitan distribution worldwide, so this is potentially a non-native.

Similar Species: Could be confused with other caprellids; especially Caprella fretensis but close inspection of the 3rd segment of antenna 1 should help distinguish between the two.

Key Identification Features:

• Smooth head and body.
• Rostrum not clearly differentiated from head.
• Swimming setae on antenna 2.
• 3rd segment on antenna 1 more than half the length of segment 2.

Distribution Map from NBN: Caprella equilibra at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Caprella equilibra at iNaturalist World Species Observations database.

WoRMS: Caprella equilibra at World Register of Marine Species.