Invasion History

First Non-native North American Tidal Record: 1998
First Non-native West Coast Tidal Record: 1998
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:


North American Invasion History:


Calanoid copepods of the family Stephidae are typically small (less than 1mm in total length). And hyperbenthic, occurring primarily in the benthic boundary layer, and only occasionally in the plankton. Stephos copepods tend to have a somewhat inflated cephalothorax, and a short urosome (Ohtsuka and Hiromi 1987). In Stephos pacificus, the head is separated from the 1st metasomal segment, and the 4th and 5th segments are partially fused. The overall shape of the prosome (cephalothorax) is broadliy ova. The posterior corners of the prosome are symmetrical,, and protrude to about 1/4 of the length of the genital segment. The urosome has 4 segments. The genital segment is expanded ventrally, with curved rows of minute spinules. A sausage-shaped spermatophore is often attached to the genital segment. The rims of the 2nd and 3rd segments are lined with fine spinules. The anal segment is small, and the caudal rami are slightly longer than broad. The antennules have 24 segments, and are symmetrical. Swimming leg pairs 1-4 are biramous, with SL 1 having 3 segments on the exopod, and 1 on the endopod; SL 2 has 3 exopod segments and 2 endopod segments, and SL 3 and 4 have 3 exopod segments and 3 endopod segments. The 4 lpair of legs are progressively longer to the posterior, but the 5th pair is greatly reduced, and nearly symmetrical. With the left and right proximal segments fused. The posterior part of the terminal segments has a finely serrated fringe (Ohtsuka and Hiromi 1987). The type female is 0.73 mm long (Ohtsuka and Hitomi 1987).

The adult male is slightly smaller and thinner than the female, 0.67 mm, for the paratype specimen. The posterior corners of the prosome are slighly asymmetrical, with the left posterior corner slightly prolonged. The urosome has 5 segments. The genital segment is asymmetrical, swollen on the left side. The 1st urosome segment is slightl;y asymmetrical, swollen on the left side, while the 2nd segment has a short posteroventrl process. The posterior rims of 3rd and 4th segments are lined with fine setae. The 1st segment of the antennule bears a long, swollen aesthetasc,a specialized olfactory organ. The 5th pair of swimming legs is highly modifed, with 4 segments on the right leg and 5 segments on the left leg The basal part of the 3rd segment of the right leg is produced into an angular process, while the distal oportion is greatly elongated, and the last segment is also elongated and sickle-like, The 2nd segment of the left leg is elongated, with a row of fine spinules along its length, white the the 3rd segment ends in 5 thick spines (Ohtsuka and Hiromi 1987).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Maxillopoda
Subclass:   Copepoda
Order:   Calanoida
Family:   Stephidae
Genus:   Stephos
Species:   pacificus


Potentially Misidentified Species

Parastephos esterlyi
Described from San Diego Bay, in powerplant intake (Fleminger 1988)

Parastephos occatum
Described from Puget Sound (Damkaer 1971)

Stephos robustus
Native to NW Pacifc (Ohtsuka and Hiromi 1987)



Copepods of the genus Stephos inhabit the benthic boundary layer, on sea-bottoms, anchihaline caves, polar icefloes, a(Suárez-Morale et al. 2017; Ohtsuka and Hiromi 1987). Ohtsuka (1984) made collections of these copepods with a sledge 3-14 cm above the bottom. However, adults occasionally occur in the plankton. Sexes in copepods are separate. Males use their modified 5th pair of swimming legs to grasp the female and transfer spermatophores to the female's genital segment. In different species, eggs can be carried in sacs by females, or scattered singly in the water column. Calnoid copepod eggs hatch into a Nauplius 1, with 3 pairs of appendages (antennule, antenna, mandible), and go through 5 nauplius stages with successively more appendages, and metamorphosing into a Copepodite 1 stage, with adult-like head appendages, and 2 pairs of swimming legs. There are 5 copepodite stages before molting to the adult stage, with 5 pairs of swimming legs, and differentiated 5th swimming legs. The nauplius stages are described and illustrated for the Antarctic species, S. longipes, associated with ice floes (Costanzo et al. 2002).

As noited above, coeppods of the genus Stephos occur primarily in the boundary layers of bottoms and surfaces in marine environments. The gut contents of S. pacificus in Japan consisted of ciliates, benthic diatoms, crustacean parts, and unidentified remains( Ohtsuka and Hiromi 1987).


Phytoplankton; microzooplankton


Fishes, other zooplankton

Trophic Status:




General HabitatUnstructured BottomNone
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Maximum Length (mm)0.7Adult female body length, type specimen (Ohtsuka and Hiromi 1987)
Minimum Width (mm)0.6Adult male body length, paratype specime (Ohtsuka and Hiromi 1987)
Broad Temperature RangeNoneWarm-temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3b None 1987 Native Estab
NEP-IV Puget Sound to Northern California 1998 Def Unk
P290 Puget Sound 1998 Def Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Brylinski, Jean-Michel ; Courcot, Lucie (2019) Report of two Mediterranean species of Stephos T. Scott, 1892 (Copepoda: Calanoida) in the North-East Atlantic Ocean (Brittany, France), with a note on the “hyaline sheath” in the genus Stephos, BioInvasions Records 8: 357-368

Cordell, Jeffrey (1998) Asian copepods in Pacific Northwest estuaries., Puget Sound Notes 41: 1-7

Costanzo, G.; Zagami, G.; Crescenti, N.,;Granata, A (2002) Naupliar development of Stephos longipes (copepoda: calanoida) from the annual sea ice of terra nova bay, antarctica, Journal of Crustacean Biology 22(4): 855-860

Damkaer, David M. (1971) Parastephos occatum, a new species of hyperbenthic copepod from the inland marine waters of Washington State, Proceedings of the Biological Society of Washington 83(45): 503-514

Dukes, Jeffrey S., Mooney, Harold A. (1999) Does global change increase the success of biological invaders?, Trends in Ecology and Evolution 14(4): 135-139

Fleminger, Abraham (1988) Paratephos esterlyi, a new species of copepod (Stephidae; Calanoida: Crustacea) from San Diego Baym California, Proceedings of the Biological Society of Washington 101((2)): 309-13

Moon, Seong Yong; Soh, Ho Young; Cho, Dae Hyun (2020) Three new species of the genus Scott, 1892 (Crustacea, Copepoda, Calanoida,, ZooKeys 944: 1-30

Ohtsuka, Susumu (1984) Calanoid copepods collected from the near-bottom n Tanabe Bay on the pacific coast of the middle honshu, Japan. i. Arietellidae, Publications from the Biological Station, Espegrend 29(4-6): 359-365

Ohtsuka, Susumu, Hiromi, Juro (1987) Calanoid copepods collected from the near-bottom in Tanabe Bay on the Pacific coast of the Middle Honshu, Japan. III. Stephidae, Publications of the Seto Marine Biological Laboratory 32(4/6): 219-232

Ohtsuka, Susumu; Hiromi, Juro (1987) Calanoid Copepods from the near-bottom in Tanabe Bay on the Pacific Coast of the middle Honshu, Japan, Publications of the Seto Marine Biological Laboratory 32(4/6): 219

Razouls, C.; de Bovée, F.; Kouwenberg, J.Desreumaux, N. 2005-2012 Diversity and geographic distribution of marine planktonic copepods. <missing URL>

Suárez-Morales, Eduardo; Gutiérrez-Aguirre, Martha A.; Cervantes-Martínez, Adrián; Iliffe, Thomas M. (2017) A new anchialine Stephos Scott from the Yucatan Peninsula with notes on the biogeography and diversity of the genus (Copepoda, Calanoida, Stephidae), ZooKeys 67: 1–17