BIOTIC Species Information for Jassa falcata
Researched byJacqueline Hill Data supplied byMarLIN
Refereed byProf. P. Geoff Moore
Scientific nameJassa falcata Common nameAn amphipod
MCS CodeS569 Recent SynonymsNone

PhylumCrustacea Subphylum
Superclass ClassEumalacostraca
SubclassPeracarida OrderAmphipoda
SuborderGammaridea FamilyIschyroceridae
GenusJassa Speciesfalcata

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).
Taxonomy References Howson & Picton, 1997, Hayward & Ryland, 1995b, Fish & Fish, 1996, Lincoln, 1979, Conlan, 1990,
General Biology
Growth formArticulate
Feeding methodPredator
Active suspension feeder
See additional information
Temporary attachment
Environmental positionEpibenthic
Typical food typesUnselective suspension feeder of detritus and small organisms. HabitTubiculous
Bioturbator FlexibilityHigh (>45 degrees)
FragilityIntermediate SizeSmall(1-2cm)
HeightInsufficient information Growth Rate0.07 mm/day
Adult dispersal potential10-100m DependencyIndependent
General Biology Additional Information
  • Jassa falcata builds tubes, from debris, among algae and hydroids, and on solid surfaces and structures. Males and females live in separate tubes constructed of pieces of debris cemented together, the tubes often forming dense mats.
  • This species is essentially a benthic tube dwelling amphipod although intermittent swimming and crawling is common.
  • Jassa falcata is generally a suspension feeder, however, large specimens have also been seen to capture and feed upon other smaller amphipods and ostracods to supplement their diet.
  • Growth rate is given as maximum growth rate observed in laboratory investigations at varying temperatures. Maximum growth took place at 20 °C (Nair & Anger, 1979).
Biology References Hayward & Ryland, 1995b, Fish & Fish, 1996, Baardseth, 1970, Nair & Anger, 1979, Conlan, 1990,
Distribution and Habitat
Distribution in Britain & IrelandFound on all British coasts. Reported from several sites around the coast of Ireland.
Global distributionCosmopolitan in temperate and warm-temperate waters; widespread and frequently recorded in Atlantic, Pacific and Indian Oceans, both north and south of the equator. Reported from most coastal regions of North East Atlantic, and often locally abundant.
Biogeographic rangeNot researched Depth rangeLower eulittoral to 5 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationThis species is an important fouling organism. The animals construct tubes from pieces of debris and sediment cemented together, often forming dense mats, particularly in warm water discharge pipes from power stations (Fish & Fish, 1996).

Reported to depths of 5m in Japan (Kamenskaya, 1977). Jassa falcata is often found inhabiting Laminaria holdfasts and so may be found at the greater depths inhabited by some kelps.
Jassa falcata appears to be out-competed by Parajassa pelagica or unable to survive in very strong wave action at shallow depths (K. Hiscock personal communication).

Substratum preferencesOther species (see additional information)
Artificial (e.g. metal/wood/concrete)
Physiographic preferencesOpen coast
Strait / sound
Enclosed coast / Embayment
Biological zoneLower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Wave exposureVery Exposed
Moderately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Hayward & Ryland, 1995b, Lincoln, 1979, Picton & Costello, 1998, Costello et al., 1989,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismDirect Development
Reproductive SeasonAll year Reproductive LocationInsufficient information
Reproductive frequencyAnnual protracted Regeneration potential No
Life span<1 year Age at reproductive maturity<1 year
Generation time<1 year FecundityInsufficient information
Egg/propagule sizeInsufficient information Fertilization typeExternal
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodNot relevant
Duration of larval stageNot relevant   
Reproduction Preferences Additional Information
  • Reproduction, and therefore production of gametes, occurs throughout the year although some seasonal peaks of reproduction have been observed. In Helgoland waters, for example, two peaks were observed, the main one in summer and another smaller peak in winter (Nair & Anger, 1980).
  • The mating system is polygynous. Several broods of offspring are produced, each potentially fertilised by a different male. Males are believed to seek out mature females attracted by female pheromones.
  • There is no sperm storage, and fertilisation is external.
  • There is no larval stage. Embryos are brooded in a marsupium, beneath the thorax, formed by the oostegites (a series of flattened plates projecting from basal segments). Embryos are released as subjuveniles with incompletely developed eighth thoracopods and certain differences in body proportions and pigmentation.
  • In laboratory investigations, life span, time to maturity and fecundity were strongly influenced by temperature (Nair & Anger, 1979). At 20 °C the time to reach maturity is 2 months, about half the value observed at 10 °C. Field investigations in Helgoland observed age at maturity to be 6 months for new generations produced in low winter temperatures of 7-8 °C (Nair & Anger, 1980).
  • Growth rate also increases with increasing temperature but life span is shorter and individuals are smaller at higher temperatures (Nair & Anger, 1979).
Reproduction References Barnes, 1980, Nair & Anger, 1979, Nair & Anger, 1980,
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