BIOTIC Species Information for Neomysis integer
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Researched byGeorgina Budd Data supplied byMarLIN
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Scientific nameNeomysis integer Common nameAn opossum shrimp
MCS CodeS76 Recent SynonymsNone

PhylumCrustacea Subphylum
Superclass ClassEumalacostraca
SubclassPeracarida OrderMysidacea
SuborderMysida FamilyMysidae
GenusNeomysis Speciesinteger

Additional InformationThe species seems to be particularly susceptible to injury, causing atypical morphology which may lead to misidentification (Hayward & Ryland, 1995). Synonyms of Mysis or Neomysis vulgaris were in use in the early and continental literature, though Tattersall & Tattersall (1951) considered the specific integer (Leach) to have priority (Parker, 1979).
Taxonomy References Hayward & Ryland, 1995b, Makings, 1977, Mauchline, 1980, Tattersall & Tattersall, 1951, Parker, 1979, Barnes, 1994,
General Biology
Growth formArticulate
Feeding methodActive suspension feeder
Environmental positionEpibenthic
Typical food typesDetritus, diatoms, filamentous algae and small crustaceans. HabitFree living
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityIntermediate SizeSmall(1-2cm)
HeightNot relevant Growth Rate1-2 mm/month
Adult dispersal potential100-1000m DependencyIndependent
General Biology Additional InformationGrowth rate
In mature adults from the Ythan Estuary, Scotland, growth rate was recorded to be 1-2 mm per month in the field, which followed a rapid period of growth, of 4-5 mm per month in the summer juveniles (Astthorsson, 1980). The winter generation had a growth rate of 3-4 mm monthly for juveniles and about 1 mm per month for mature adults. During the winter there was a period of about 3 months when growth ceased (Astthorsson & Ralph, 1984).
Swimming behaviour
Neomysis integer performs a diel vertical migration, rising towards the surface waters during the night and returning to the deeper waters at daylight where it remains throughout the day (Hough & Naylor, 1992). Normal diurnal light levels are inhibitory and produce a negatively phototactic response in most species; the 24 hour cycle of change in ambient light intensity is the dominant factor controlling the diel vertical migration of mysids, such as Neomysis integer (Mauchline, 1980).
Maintenance of position
As a pelagic organism, Neomysis integer faces the problem of retaining its position within the estuarine environment, against conditions of net seaward transport (Hough & Naylor, 1992). In general, there are three main controls of the positioning of pelagic invertebrate populations in estuarine systems: reproductive compensation of seaward losses (a relatively large number of juveniles are produced per brood, behavioural adaptations (alterations in swimming activity at different tidal phases) and hydrodynamic process (distribution directly related to patterns of water circulation) (Schlacher & Wooldridge, 1994).
In laboratory experiments, Hough & Naylor (1992) found Neomysis integer to have an endogenously controlled circa-tidal swimming activity, with peak swimming activity expressed during the ebb tide. In the investigation of the significance of its endogenously controlled ebb tide swimming, Hough & Naylor (1992) observed Neomysis integer to demonstrate rheotaxic behaviour. Typically on the ebb tide in the Conway Estuary, shallow pools of isolated water are left as the tide ebbs. Aggregations of Neomysis integer in imminent risk of stranding initially headed into the current, but as the water level dropped, and before a pool was completely cut off, the species swam with the current draining from the pool and entered the stream before finally re-orientating and swimming into the current. Hough & Naylor (1992) suggested that such rheotaxic behaviour coupled a continuous ebb-phased swimming rhythm, may be of importance in the avoidance of stranding on the shore at low tide.
Maximum swimming speed by the mysid is also important, since it dictates in which flow velocities the species can maintain its position. Specimens studied by Roast et al. (1998b) from the East Looe River Estuary (Cornwall) tolerated current velocities of 6 and 9 cm s-1, a few could swim at speeds of up to 27cm s-1, but was not sustainable for more than a few seconds. Roast et al. (1998b) found the swimming speeds of Neomysis integer correlated well with the distribution of the species in the East Looe River Estuary, where mysids were found consistently in slower moving water (<15 cm s-1) and were absent in faster flowing water (>20 cm s-1). Roast et al. (1998b) stated that if swimming speed is an important factor in the position maintenance of the species, it is likely to be beneficial for the mysid to utilize any available shelter in order to conserve energy. In experimental conditions, Roast et al. (1998b) observed Neomysis integer to attach themselves to the substratum, thereby entering the boundary layer where lower velocity flows are experienced. This corresponds with field studies, for instance in the Conway Estuary, North Wales, Neomysis integer was always caught in greatest abundance in near-bottom plankton samples (Hough & Naylor, 1992). On the ebb tide, during flood and high-tide periods in the Ythan Estuary, Scotland, the species was concentrated in a band toward the moving tide edge where flows were typically lower. Also on the ebb tide and at low tide the species aggregated in shallower water and in the lee of rocks and macroalgal clumps where water flow rates were less than 10 cm/sec (Lawrie et al.,1999). Shallow burrowing into the sediment is also a common means of position maintenance in moving waters, and is a common behaviour of mysids inhabiting areas subject to tidal disturbance (Roast et al., 1998b).
Biology References Makings, 1977, Mauchline, 1980, Tattersall & Tattersall, 1951, Mauchline, 1971, Astthorsson, 1980, Hough & Naylor, 1992, Lawrie et al., 1999, Barnes et al., 1979, Astthorsson & Ralph, 1984, Schlacher & Wooldridge, 1994, Roast et al., 1998b,
Distribution and Habitat
Distribution in Britain & IrelandRecords indicate Neomysis integer to have a widespread, but patchy distribution on all British and Irish coasts in locations of lowered salinity, usually estuaries or brackish water enclosures.
Global distributionDistributed from Artic Norway to the Atlantic coast of Spain.
Biogeographic rangeNot researched Depth range5-10 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationSalinity tolerance
Neomysis integer is a euryhaline species normally found in locations with salinities in the range 0.5 - 20 psu. However, it may be found more rarely in adjacent isolated waters of salinities greater than 20 psu, and in freshwaters. For instance, Neomysis integer adapted successfully to the transition from brackish lagoon to freshwater lagoon in the case of Loch Mor Barvas, Isle of Lewis, Scotland (Barnes, 1994).

Substratum preferencesCoarse clean sand
Gravel / shingle
Water column (pelagic)
Physiographic preferencesSealoch
Isolated saline water (Lagoon)
Biological zoneUpper Infralittoral
Lower Infralittoral
Wave exposureSheltered
Very Sheltered
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
SalinityLow (<18 psu)
Reduced (18-30 psu)
Habitat Preferences Additional Information
Distribution References Hayward & Ryland, 1995b, Makings, 1977, Parker, 1979, JNCC, 1999, Barnes, 1994, Parker & West, 1979,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismOvoviviparous
Reproductive SeasonSpring to Autumn Reproductive LocationAs adult
Reproductive frequencyAnnual protracted Regeneration potential No
Life span<1 year Age at reproductive maturity<1 year
Generation time<1 year FecundityUp to ca 50
Egg/propagule sizeInsufficient information Fertilization typeInsufficient information
Larval/Juvenile dispersal potential100-1000m Larval settlement periodNot relevant
Duration of larval stageNot relevant   
Reproduction Preferences Additional InformationThe life history and biology of Neomysis integer differs slightly between localities (Mees et al., 1994; Astthorsson, 1980; Parker & West, 1979; Mauchline, 1971; Ralph, 1965; Kinne, 1955; Vorstman, 1951). Apparently the local environmental factors, especially temperature, have an influential role in determining the duration of the breeding season and the number of generations produced per year. Typically there are three generations per year.
For instance, in a population from Loch Etive, studied by Mauchline (1971), the over-wintering members consisted predominantly of juveniles and immature males and females. Once mature they began an intensive period of breeding in the spring. The spring generation matured rapidly and bred during late June and early July, which consequently produced a third generation in the autumn. These intensive periods of breeding were set against a background of continuous breeding throughout the year, so that discrete generations were not evident, but modal age groups within the population could be traced over weeks, or in the case of the over-wintering population, a few months.
However, outside periods of intensive breeding the recruitment rate was lower: < 1% of females carried eggs and broods were smaller. Brood size in mysid shrimps has been found to be related to female body length and season (Mauchline, 1971). A winter brood of Neomysis integer from Loch Etive consisted of between 10-25 juveniles compared to 20-50 in the summer.
In contrast, to the population of Neomysis integer from Loch Etive, a population from the Ythan estuary on the east coast of Scotland studied by Astthorsson (1980), produced only two generations per year with a complete cessation of breeding during winter. Temperature differences between the two locations were implicated as the Ythan estuary had a much lower summer maximum temperature than Loch Etive (17°C cf. 20°C; Leach, 1971; Gage, 1974).
Reproduction References Makings, 1977, Mauchline, 1971, Astthorsson, 1980, Vorstman, 1951, Ralph, 1965, Parker & West, 1979, Kinne, 1955, Mees et al., 1994, Gage, 1974, Leach, 1971,
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