Invasion History

First Non-native North American Tidal Record: 1960
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1960

General Invasion History:

The mysid Praunus flexuosus is native to northern Europe, from Brittany to ' the coasts of Scandinavia' and the Baltic Sea, east to Finland (Tattersall and Tattersall 1951). It occurs in coastal waters, estuaries and tidepools (Tattersall and Tattersall 1951). It has been introduced to Iceland (Astthorsson 1987) and the East Coast of North America from Rhode Island to Nova Scotia (Wigley 1963; Wigley and Burns 1971; Mauchline 1980).

North American Invasion History:

Invasion History on the East Coast:

Praunus flexuosus was first collected in North American waters in Barnstable Harbor, Cape Cod Bay, Massachusetts (MA) in 1960 (Wigley 1963), and was later collected from Plymouth, MA to Appledore Island, Maine (ME) (Wigley and Burns 1971). In 1967, P. flexuosus was found in the stomach of a fish in Penobscot Bay, ME (Haefner 1969). This mysid is known from many of the estuaries of the Gulf of Maine, including Massachusetts Bay, Great Bay (New Hampshire – ME), Casco Bay, Penobscot Bay, Cobscook Bay, and the Bay of Fundy (Wigley and Burns 1971; Mauchline 1980; Jackson et al. 1997; MIT Sea Grant 2003-2008; Harris and Dijkstra 2007; MIT Sea Grant 2009-2012). By 1980, it had reached the Atlantic coast of Nova Scotia, and now occurs in the Gulf of St. Lawrence (Mauchline 1980; Mees 2012). So far, the only definite record of P. flexuosus, south of Cape Cod, is from a 2010 Rapid Assessment Survey, which found this mysid near the mouth of Narragansett Bay, at Fort Adams State Park, Newport, Rhode Island (MacIntyre et al. 2011).

Invasion History Elsewhere in the World:

Praunus flexuosus was first discovered in Iceland in 1970, near Reykjavik. By 1985, it was abundant in many of the inlets on the west side of the island (Astthorsson 1987).


Mysids are small, shrimplike crustaceans, with a cape-like carapace which covers the head and thorax, but which is not attached to the last four thoracic segments. A pair of spherical statocysts is located at the base of the inner uropods. Adult females have a ventral brood pouch (Barnes 1983; Modlin 2007).

Praunus flexuosus has a slender body, often slightly bent in lateral view. The carapace is produced anteriorly into a short, rounded rostrum. The anterolateral edges of the carapace are drawn out into small, sharp points. The posterior edge of the carapace is curved anteriorly, exposing parts of the 7th and 8th thoracic segments. The eyes are large, somewhat club-shaped, with prominent stalks and kidney-shaped corneas. The antennal scale is 7-8 times as long as broad, with a bare outer margin, terminating in a sharp, articulated spine. The 4th pleopod of the male has an elongated endopod, with 7 segments, ending in a long spine. The telson is a tapered oblong, ending in a deeply (1/6 of the telson's length) cleft posterior edge, with rounded corners. The outer edges of the telson are lined with about 20-30 stout spines, with one on each outer corner. The exopod of the uropod is about 1.5 X the length of the telson, and lined with long, fine spines. The endopod is only slightly longer than the telson and also lined with spines. On the inner margin, there are 11-14 spines, more crowded distally, and more spaced out laterally. The largest reported adults are 24.5 mm (females) and 22 mm (males) in length. These mysids can change color to match their background, and can range from transparent to nearly black (Tattersall and Tattersall 1951).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Mysidacea
Suborder:   Mysida
Family:   Mysidae
Genus:   Praunus
Species:   flexuosus


Astacus harengum (Fabricius, 1787)
Cancer astacus multipes (Montagu, 1898)
Cancer flexuosus (Muller, 1776)
Macromysis flexuosa (Holt and Beaumont, 1900)
Mysis chamaeleon (Thompson, 1828)
Mysis chameleo (Nusbaum, 1887)
Mysis flexuosa (Latreille, 1818)
Mysis flexuosus (Norman, 1860)
Mysis leachii (Desmarest, 1823)
Mysis spinulosa (Kroyer, 1837)
Mysis spinulosus (Leach, 1815)
Praunus flexuosus (Stebbing, 1893)
Praunus negelectus (Zimmer, 1904)
Synmysis benedeni (Czerniavsky, 1883)
Synmysis chamaeleon (Czerniavsky, 1883)
Synmysis flexuosa (Czerniavsky, 1883)
Synmysis mecznikovi (Czerniavsky, 1883)
Synmysis normani (Czerniavsky, 1883)
Synmysis spinulosa (Czerniavsky, 1883)
Themisto brevispinulosa (Bell, 1853)

Potentially Misidentified Species

Heteromysis formosa
Native MA-FL, prominent rostrum, pink color, deeply cleft telson, with a long spine at each corner.

Mysidopsis stenolepis
Native MA-NJ, prominent rostrum, antenna scale 12X longer than wide, telson ~4X as long as wide and deeply cleft.



Mysids are small, shrimplike crustaceans, which tend to divide their time between epibenthic habitats and the plankton, sometimes migrating diurnally, or else making brief swims between benthic habitats. Males have a pair of penes located at the junction of the thorax and abdomen, and modified pleopods used for the transfer of spermatophores - in P. flexuosus, this is pleopod 4. Adult females have a brood pouch, and give birth to broods of 27-57 juveniles, resembling miniature adults (Tattersall and Tattersall 1951; Barnes 1983; Astthorsson 1987; Johnson and Allen 2006).

Praunus flexuosus is abundant in coastal waters, tidepools, and estuaries, among grass beds, seaweeds, sand and mud. Animals often hover above the bottom with the head up, and the body hanging nearly vertically. (Tattersall and Tattersall 1951; Wigley and Burns 1971; Astthorsson 1987). In the laboratory, this mysid tolerates salinities from 2 to 33 PSU (McLuskey and Heard 1971). Food includes phytoplankton, captured by filter-feeding, and zooplankton, which may be seized individually (Tattersall and Tattersall 1951).


Phytoplankton; Zooplankton; Benthic invertebrates



Trophic Status:




General HabitatGrass BedNone
General HabitatUnstructured BottomNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatSalt-brackish marshNone
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)3Field data, England (Tattersall 1951)
Maximum Temperature (ºC)21Field data, England (Tattersall 1951)
Minimum Salinity (‰)2Experimental data, 5 C (McClusky and Heard 1971)
Maximum Salinity (‰)35Atlantic Ocean salinity. Survived transfer to 33 but not 40 or 50 ppt (McClusky and Heard 1971).
Minimum Length (mm)14.5Adults (Tattersall and Tattersall 1951)
Maximum Length (mm)24.5Adults (Tattersall and Tattersall 1951)
Broad Temperature RangeNoneCold temperate
Broad Salinity RangeNoneOligohaline-Euhaline

General Impacts

Praunus flexuosus is locally common in some invaded areas, such as the Great Bay, New Hampshire, and inlets on the west coast of Iceland (Astthorsson 1987), but no ecological or economic impacts have been reported (Harris and Dijkstra 2007).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEA-II None 0 Native Estab
NEA-III None 0 Native Estab
B-I None 0 Native Estab
AR-V None 0 Native Estab
NEA-IV None 0 Native Estab
B-II None 0 Native Estab
B-III None 0 Native Estab
B-IV None 0 Native Estab
B-V None 0 Native Estab
B-VI None 0 Native Estab
B-VII None 0 Native Estab
B-VIII None 0 Native Estab
B-X None 0 Native Estab
B-IX None 0 Native Estab
AR-IV None 1970 Def Estab
NA-ET2 Bay of Fundy to Cape Cod 1960 Def Estab
NA-ET1 Gulf of St. Lawrence to Bay of Fundy 1980 Def Estab
N130 Great Bay 2006 Def Estab
N180 Cape Cod Bay 1960 Def Estab
N170 Massachusetts Bay 1972 Def Estab
N140 Hampton Harbor 2007 Def Estab
N050 Penobscot Bay 1967 Def Estab
N010 Passamaquoddy Bay 2004 Def Estab
N135 _CDA_N135 (Piscataqua-Salmon Falls) 1972 Def Estab
N120 Wells Bay 2008 Def Estab
N100 Casco Bay 2007 Def Estab
N080 Sheepscot Bay 2007 Def Estab
NA-S3 None 0 Def Estab
NA-ET3 Cape Cod to Cape Hatteras 2010 Def Estab
M020 Narragansett Bay 2010 Def Estab
B-XI None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Astthorsson, Olafur S. (1987) Records and life history of Praunus flexuosu (Crustacea: Mysidacea) in Icelandic waters, Journal of Plankton Research 9(5): 955-964

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Haefner, Paul A. Jr. (1969) Occurrence of a larval alligator fish (Agonidae) in brackish water., Copeia 1969: 201-202

Harris, Larry G.; Dijkstra, Jennifer A. (2007) <missing title>, New Hampshire Estuaries Project, <missing place>. Pp. <missing location>

Jackson, C. J.; Marcogliese, C. J.; Burt, M. D. B. (1997) Role of hyperbenthic crustaceans in the transmission of marine helminth parasites, Canadian Journal of Fisheries and Aquatic Science 54: 815-820

Johnson, William S.; Allen, Dennis M. (2005) <missing title>, Johns Hopkins Press, Baltimore. Pp. <missing location>

Kennedy, C., Pappal, A. L.; Bastidas, C.; ; Carlton, J. T.; David, A. A.; Dijkstra, J.A.; Duffey, S; Gibson, J.; Grady, S. P.; Green-Gavrielidis, (2020) Report on the 2018 Rapid Assessment Survey of Introduced, Cryptogenic, and Native Marine Species at New England Marinas: Massachusetts to Maine, <missing publisher>, Boston MA. Pp. <missing location>

MacIntyre, Chris; Adrienne Pappal; Pederson, Judy; Smith, Jan P. (2011) Marine Invaders in the Northeast Rapid Assessment Survey of non-native and native marine species of floating dock communities, Massachusetts Coastal Zone Management, Boston MA. Pp. <missing location>

Massachusetts Office of Coastal Zone Management (2013) Rapid assessment survey of marine species at New England floating docks and rocky shores, Massachusetts Office of Coastal Zone Management, Boston MA. Pp. <missing location>

Mauchline, John (1980) The biology of mysids, Advances in Marine Biology 18: 3-369

McLusky, D. S.; Heard, V.E. J. (1971) Some effects of salinity on the mysid Praunus flexuosus., Journal of the Marine Biological Association of the United Kingdom 51: 709-715

Mees, J. 2012 <i>Praunus flexuosus</i>. In Canadian Registry of Marine Species. <missing URL>

MIT Sea Grant 2003-2008 Introduced and cryptogenic species of the North Atlantic. <missing URL>

MIT Sea Grant 2009-2012 Marine Invader Tracking and Information System (MITIS). <missing URL>

Modlin, Richard F. (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California, Berkeley CA. Pp. 489-485

Newell, G. E.; Newell, R. C. (1977) <missing title>, Hutchinson & Co., London. Pp. <missing location>

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>

Tattersall, W. M., Tattersall, Olive M. (1951) <missing title>, Ray Society, London. Pp. <missing location>

Trott, Thomas J. (2004) Cobscook Bay inventory: a historical checklist of marine invertebrates spanning 162 years., Northeastern Naturalist 11(Special issue 2): 261-324

Wigley, Roland L. (1963) Occurrence of Praunus flexuosus (O. F. Müller) (Mysidacea) in New England waters., Crustaceana 6: 158

Wigley, Roland L.; Burns, Bruce R. (1971) Distribution and biology of mysids (Crustacea, Mysidacea) from the Atlantic coast of the United States in the NMFS Woods Hole collection, Fishery Bulletin 69(4): 717-746

Zettler, Michael L.; Daunys, Darius (2007) Long-term macrozoobenthos changes in a shallow boreal lagoon: Comparison of a recent biodiversity inventory with historical data., Limnologica 37: 170-185