Description: This amphipod is yellow to grey in colour with strong brown, red or black striping and marking. It reaches up to 7 mm in size and lives in self-constructed tubes. Eyes are small, round and dark in colour. The accessory flagellum is distinct and made up of two sections. Uropod 3 branches into two (biramous), the outer ramus has a hooked spined towards the rear and 1-3 teeth placed distolaterally. In males the gnathopods can help with identification, although there can be a lot of variation between individuals. In males the propodus of gnathopod 2 is very enlarged and has a small distal tooth and a large proximal process. In females the propodus is also large but the gnathopods differ slightly in shape from the male and there is no proximal projection. The telson is small and triangular, with two bristles on each side.

Habitat: Lives in tubes built from debris, either on solid structures (e.g. pilings, hulls of ships, buoys) or amongst algae and hydroids. Can be very common on ships and in harbours/marinas. Found both intertidally and sublittorally.

Distribution: Recorded from all around Britain and Ireland and seems to be widespread and the most common Jassa species here. However, there has been some confusion over identification of Jassa species, especially distinguishing between J. falcata, J. herdmani and J. marmorata.

Similar Species: Jassa species may be easily confused, and there are a number of superficially similar looking amphipods found in Britain and Ireland so careful inspection, using a microscope, and use of specialist identification guides may be required.

Key Identification Features:

• Yellow to grey with strong markings in brown, black or red.
• Lives in tubes constructed from debris.
• Accessory flagellum distinct and has 2 sections.
• Uropod 3 biramous; outer ramus with hooked spine and 1-3 teeth.
• In males gnathopod 2 very enlarged with small tooth and large process.
• Small, triangular telson with 2 setae on each side.

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

iNaturalist: Jassa falcata at iNaturalist World Species Observations database.

GBIF data for Jassa marmorata

WoRMS: Jassa falcata at World Register of Marine Species. Accepted name: Jassa marmorata Holmes, 1905. AphiaID: 102433.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Peracarida; Amphipoda; Senticaudata; Corophiida; Caprellidira; Photoidea; Ischyroceridae; Ischyrocerinae; Ischyrocerini; Jassa