Biodiversity & Conservation

An amphipod - Jassa falcata

Jassa falcata

Image - Jassa falcata Image width ca XX cm.
Image copyright information

  • #
  • #
  • #
Distribution map

Jassa falcata recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

Sightings Have you seen Jassa falcata?
If so please submit your record.

Jassa falcata is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Arthropoda Arthropods, joint-legged animals, e.g. insects, crustaceans & spiders
Class Malacostraca Crabs, lobsters, sand hoppers and sea slaters
Authority Montagu, 1808
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland Found on all British coasts. Reported from several sites around the coast of Ireland.
Habitat information icon Habitat information Jassa falcata constructs tubes from debris amongst algae, hydroid growths and on solid surfaces in sediment and areas of strong water currents such as pilings, buoys, rafts or the hulls of ships. It is an important fouling organism because the tubes of Jassa falcata often form dense mats or 'nests'. Also found in Laminaria spp. holdfasts and similar habitats.
Text page icon Description A tube dwelling amphipod, elongate and rather flattened up to 13 mm in length. Colour varied, often yellow-grey with brown, red or black patches depending the colour of the surrounding habitat. Eyes small, round and dark.
Identifying features
  • Antennae 1 bears a two segmented accessory flagella and is shorter and more slender than antennae 2.
  • Gnathopod 2 larger than gnathopod 1, terminating in characteristic claw which differs in size and form between sexes.
  • In adult males, gnathopod 2 propodus is greatly enlarged, with a stout thumb opposing the dactylus.
  • Uropod 3 biramous, outer ramus with hooked spine and 1-3 small teeth.
  • Telson small, triangular, with two setae on each side of apex.
Additional information icon Additional information
  • Jassa falcata shows marked variation in shape and relative proportions of the taxonomically useful characteristics vary with growth stage.
  • Therefore, the taxonomy of Jassa falcata has proved to be problematic.
  • The species Jassa marmorata and Jassa herdmani are easily confused with Jassa falcata so that some of the literature on Jassa falcata may refer to these species or a mixture of Jassa species (Conlan, 1990).

Want to know more? more

This review can be cited as follows:

Jacqueline Hill 2000. Jassa falcata. An amphipod. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 03/09/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=3581>