Invasion History

First Non-native North American Tidal Record: 1977
First Non-native West Coast Tidal Record: 1977
First Non-native East/Gulf Coast Tidal Record: 2014

General Invasion History:

Deltamysis holmquistae was described from the Sacramento-San Joaquin Delta, but very little is known about the distribution and origin of this species. The relatively recent (1977) appearance of D. holmquistae, in the long-monitored San Francisco estuary, and its lack of relationship to native mysids is strongly suggestive of introduction (Bowman and Orsi 1992; Cohen and Carlton 1995). The most similar known genera are Burrimysis, known from a saline lake in a cave in Balearic Islands, Spain (Bowman and Orsi 1992) and Kochimysis, known from an estuary in India (Panampunnayil and Biju 2007).

North American Invasion History:

Invasion History on the West Coast:

In August and September 1977, Deltamysis holmquistae was collected from the upper San Francisco Bay estuary, between Jersey Island and Browns Island, in the Sacramento-San Joaquin Delta. It has been collected in San Pablo Bay, its seaward limit (Bowman and Orsi 1992). In November to January 2002/2003, it was collected several times in marshes at China Camp, San Pablo Bay (Dean et al. 2005). In general, collections of this mysid are rare and sporadic. This could stem from low abundance and/or lack of knowledge of its preferred habitat. The tribe Heteromysini, to which it belongs, is largely epibenthic or commensal, and often associated with vegetation (Bowman and Orsi 1992). So far, it is known from salinities of 0 to 32.5 PSU, but is most abundant at 1.1-2.2 PSU (Bowman and Orsi 1992; Dean et al. 2005). Ranasinghe et al. (2006) report Deltamysis sp. (possibly D. holmquistae) from the more marine Alamitos and San Diego Bays, but gave no details on its morphology or identity.


The mysid Deltamysis holmquistae is known from fresh and brackish waters of the San Francisco estuary. A Deltamysis sp. has been reported from high salinity estuaries in Southern California (Ranasinghe et al. 2005), but no details are available on its morphology or identity. It belongs to the Heteromysini, which includes many geographically scattered epibenthic genera. One recently described species and genus, Kochimysis pillaii, from India, has many morphological similarities (Panampunnayil and Biju 2007).

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. The carapace of D. holmquistae has a notch on the posterior edge, exposing the 7th thoracic segment. The rostrum is short and rounded when viewed from above. The eyestalks are short, about as long as the eye. Both are about 1.5X wide as long, relatively short for mysids. In the male, a penis, about 5X as long as wide, is located at the boundary between the thorax and abdomen, adjacent to each 7th thoracic legs. The telson is shaped like a rounded, truncated triangle, 1.2X long as wide, with a smooth outline, and seven pairs of marginal spines. These include 4-5 pairs of lateral spines, increasing in length posteriorly, two subapical pairs and one short apical pair. The uropod is about 1.7X the length of the telson. The exopod is slightly longer than the endopod. Adult D. holmquistae are 3-6 mm long. Description based on Bowman and Orsi 1992, Mecum 2006, and Modlin in Carlton 2007.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Mysidacea
Suborder:   Mysida
Family:   Mysidae
Genus:   Deltamysis
Species:   holmquistae</erm>


Kochimysis pillai (Panampunnayil & Biju, 2007, 2007)

Potentially Misidentified Species



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 D. holmquistae this is pleopod 5. Adult females have a brood pouch, and give birth to juveniles, resembling minature adults (Barnes 1983; Bowman and Orsi 1993; Modlin, in Carlton 2007).

Deltamysis holmquistae is known from tidal freshwater to marine habitats in San Francisco Bay, Florda estuariies, and the Indian Ocean (Bowman and Orsi 1993; Panampunnayil and Biju 2007; Scripter et al. 2020). It is rare, and its distribution is poorly known, but it belongs to a taxonomic tribe (Heteromysini) which tends to have epibenthic or commensal habits. It is believed to be associated with vegetation in marshes and/or submerged vegetation (Bowman and Orsi 1992; Dean et al. 2005). Mysids may be epibenthic feeders, suspension feeders, predators, or omnivores (Barnes 1983).


Phytoplankton; Zooplankton

Trophic Status:




General HabitatGrass BedNone
General HabitatUnstructured BottomNone
General HabitatSalt-brackish marshNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Life History

Tolerances and Life History Parameters

Minimum Temperature (ºC)13.7From Jacksonville FL (Scripter et al. 2020)
Maximum Temperature (ºC)32.5From Cochin Backwater, India (Panampunnayil and Biju, 2007, as Kochimysis et al. 2007)
Minimum Salinity (‰)0Field data, San Fracisco Bay Delta (Cohen and Carlton 1995).
Maximum Salinity (‰)32.5From Cochin Backwater, India (Panampunnayil and Biju, 2007, as Kochimysis et al. 2007)
Minimum Length (mm)3Adults (Bowman 1992)
Maximum Length (mm)6Adults (Bowman 1992; Mecum 2006)
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNoneNontidal Limnetic-Mesohaline

General Impacts

No economic or ecological impacts are known for the mysid Deltamysis holmquistae.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-V Northern California to Mid Channel Islands 1977 Def Estab
P090 San Francisco Bay 1977 Def Estab
CAR-VII Cape Hatteras to Mid-East Florida 2014 Def Estab
S180 St. Johns River 2014 Def Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 2015 Def Estab
S196 _CDA_S196 (Cape Canaveral) 2015 Def Estab
S190 Indian River 2018 Def Estab
G270 Brazos River 2016 Def Estab
CIO-I None 2007 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
27762 Bowman and Orsi 1992 1984 1984-01-01 Decker Island, Sacramento River Def 38.0904 -121.7191
31087 Bowman and Orsi 1992 1984 1984-01-01 Delta General Location Def 38.0599 -122.2580
31104 Bowman and Orsi 1992 1984 1984-01-01 Delta General Location Def 37.9999 -121.5707
33408 Bowman and Orsi 1992 1983 1983-01-01 Point San Pablo Def 37.9652 -122.4285


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

Bowman, Thomas E.; Orsi, James J. (1992) Deltamysis holmquistae, a new genus and species of Mysidacea from the Sacramento-San Joaquin estuary of California, Proceedings of the Biological Society of Washington 105(4): 733-742

Carlton, James T. (Ed.) (2007) The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon Fourth Edition, Completely Revised and Expanded, University of California Press, Berkeley. Pp. <missing location>

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Dean, Amy F.; Bollens, Stephen M.; Simenstad, Charles; Cordell, Jeffery (2005) Marshes as sources or sinks of an estuarine mysid: demographic patterns and tidal flux of Neomysis kadiakensis at China Camp marsh, San Francisco estuary, Estuarine, Coastal and Shelf Science 63: 1-11

McCarthy, Helen O.; Fitzpatrick, Susan; Irwin, S. W B (2002) Life history and life cycles : Production and behavior of trematode cercariae in relation to host exploitation and next-host characterisitics, Journal of Parasitology 88: 910-918 3395(2002)088[0910:LHALCP]2.0.CO;2

Mecum, W. Lee (2006) <missing title>, California Department of Fish and Game, Sacramento CA. Pp. 1-6

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

Panampunnayil, S. U.; Biju, A. (2007) A new genus and species of Heteromysini (Crustacea-Mysidacea) from the backwater of Kochi (Kerala, India), Journal of Natural History 41(29-32): 1955-1963

Ranasinghe, J. Ananda and 6 authors. (2005) The prevalence of non-indigenous species in southern California embayments and their effects on benthic macroinvertebrate communities, Biological Invasions 7: 679-686