Invasion History

First Non-native North American Tidal Record: 2000
First Non-native West Coast Tidal Record: 2000
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Harpacticella paradoxa is known from freshwater habitats (springs, streams, ponds, lakes) in Hokkaido and Honshu, Japan (US National Museum of Natural History 2012) and Yunnan Province, China. It has also been collected on Aldabra Atoll in the Indian Ocean. In 2000-2006, it was collected in Washington (Puget Sound and Columbia River) and northern California (Klamath River estuary). Its occurrence in North America appears to be a probable introduction, based on its disjunct and localized distribution, its absence in recent surveys of many adjacent estuaries, the localized Asian distribution of the genus, and the frequent occurrence of harpacticoid copepods in ballast water (Cordell et al. 2007).

North American Invasion History:

Invasion History on the West Coast:

Harpacticella paradoxa was first found in the Samish River estuary, north of Puget Sound, Washington in September 2000, and a month later was collected in the Klamath River estuary, in northern California. In 2006, it was collected in the non-tidal Columbia River in the Lake Celilo reservoir, Washington, about 150 km upstream of Portland, Oregon, the nearest shipping port (Cordell et al. 2007). This copepod was collected in surveys of freshwater invertebrates, by plankton tows, and in washings of vegetation and bottom sediment. Although 32 estuaries were sampled, H. paradoxa was found at only these three locations. Salinity at the Samish River site varied from 1-15 PSU; the other sites were 0-0.1 PSU (Cordell et al. 2007). The distribution of this copopod is somewhat puzzling, since none of the collection sites are near ports where ballast water is discharged. Transport with aquatic ornamental plants, or with releases of aquarium fish such as koi or goldfish are possible vectors, but seem more likely in urban areas.


The overall shape of Harpacticella paradoxa fits Coull's (1977) category of 'prehensile fusiform', somewhat boat-shaped, but with a narrower urosome, which is often flexed. The body is slightly flattened. Harpacticella is the only freshwater genus in its family, and H. paradoxa is the only species known from North America (Ito and Kicucki 1977; Cordell et al. 2007).

In adult females, the cepahalon is shield-shaped, with a rounded protuberance. There are five thoracic segments, the anterior four tapering slightly rearwards. The 5th segment is about half the width of the widest part of the cephalothorax, and flares posteriorly. The urosome consists of five segments. The genital segment is about as wide as the 5th thoracic segment, but the rest of the urosome is slightly tapered rearwards. The caudal rami are about as wide as they are long. Counting from the outside, setae 3 and 4 are longest. The antennule consists of 7 segments – the last 3 are very short and tapered. The overall length of the antennule is less than half the width of the cephalon (Ishida 1987). The antenna has a lateral seta on the second segment of the antennal exopodite, not present in other members of the genus. The first thoracic leg (P1) is distinctive. 'The exopod is longer than the endopod and consists of 2 long segments without any inner setae. The rudiment of the third exopod segment is embedded in the second segment and bears several curved claws and a seta. The endopod has 2 or 3 segments with one large curved claw (and sometimes a small secondary claw) and a seta.' (Cordell et al. 2007). The females 5th leg has 5 setae, and the legs are twice as long as wide. Females of this family carry a single egg mass. Females are about 0.8 mm long. Description based on: Ito and Kikuchi 1977, Ishida 1987, and Cordell et al. 2007.

Adult males generally resemble the females. The female antennule consists of 7 segments, like the females, but it is greatly modified, widened and flattened, with 3 terminal claws. (The related genus Harpacticus, has nine segments in the female antennule.)The 5th segment is enlarged, and bears an aesthetasc (a thick seta-like projection). Males are about 0.7 mm long (Ito and Kikuchi 1977).

Larval development of this copepod has not been described.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Maxillopoda
Subclass:   Copepoda
Infraclass:   Neocopepoda
Superorder:   Podoplea
Order:   Harpacticoida
Family:   Harpacticidae
Genus:   Harpacticella
Species:   paradoxa


Potentially Misidentified Species

Harpacticus pacificus
Marine-estuarine, NE Pacific

Harpacticus uniremis
Marine-estuarine, NE Pacific



Harpacticella paradoxa is a freshwater epibenthic harpacticoid copepod. Males mate by clasping the female with modified antennules and transferring spermatophores to the female's genital segment. Female harpacticoids usually carry a single egg mass (Barnes 1983). Nauplii are mostly benthic or epibenthic, crawling on substrates or living in sediment, but they occasionally occur in plankton (Fofonoff, personal observation).

Harpacticella paradoxa is known from springs, streams, ponds, and lakes in Asia, and has been found in estuaries and reservoirs in Western North America (Ito and Kikuchi 1977; Ishida 1979; Cordell et al. 2007). Benthic harpacticoids feed on benthic microalgae, microbes, and detritus (Barnes 1984). The full range of salinity tolerance of H. paradoxa is not known, but it has been collected at salinities as high as 15 PSU (Cordell et al. 2007). This copepod is epibenthic, often associated with vegetation, but does swim occasionally and can be collected in near-bottom plankton (Ito and Kikuchi 1977; Cordell et al. 2007).


Detritus, microalgae


fishes, mysids, amphipods

Trophic Status:

Deposit Feeder



General HabitatNontidal FreshwaterNone
General HabitatFresh (nontidal) MarshNone
General HabitatGrass BedNone
General HabitatTidal Fresh MarshNone
General HabitatSalt-brackish marshNone
General HabitatUnstructured BottomNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)0.1Field data, Klamath, Columbia, Samish rivers (Cordell et al. 2007)
Maximum Salinity (‰)15Samish estuary, Washington (Cordell et al. 2007)
Minimum Length (mm)0.7Adult males (Ito and Kikuchi 1977)
Maximum Length (mm)0.8Adult females (Ito and Kikuchi 1977)
Broad Temperature RangeNoneCold-temperate
Broad Salinity RangeNoneNontidal Limnetic-Mesohaline

General Impacts

No ecological or economic impacts have been reported for Harpacticella paradoxa.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
P140 Klamath River 2000 Def Estab
P293 _CDA_P293 (Strait of Georgia) 2000 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Cordell, Jeffery R.; Draheim, Robyn; Sytsma, Mark (2007) First record of the harpacticoid genus Harpacticella in the Pacific Northwest, USA: another probable introduction., Aquatic Biology 1: 17-20,

Coull, Bruce C. (1977) Marine fauna and flora of the Northeastern United States. Copepoda: Harpactacoida, NOAA Technical Report NMFS Circular 399: 1-49

Ishida, Teruo (1987) Freshwater harpacticoid copepods of Hokkaido, northern Japan, Scientific Reports of the Hokkaido Salmon Hatchery 41: 77-119

Ito, Tatsunori; Kikuchi, Yoshiaki (1977) On the occurrence of Harpacticella paradoxa (Brehn) in Japan: A fresh-water harpacticoid originally described from a Chinese Lake, Annotationes Zoologiacae Japonenses 50(1): 40-56

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. <missing description>