MIT Sea Grant Center for Coastal Resources

Introduced Species - Descriptions

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Chlorophyta (Green Algae)

Codium fragile subspecies tomentosoides
Common Name: Green Fleece Alga
This is a green spongy, finger-like, branched alga that can grow up to 36 inches (91 cm). Originally introduced from Asia, it has invaded North America from Gulf of St. Lawrence (New Brunswick side of Chaleur Bay) to North Carolina, establishing populations in bays and subtidal zones. It attaches itself to hard surfaces, rocks, and shellfish.

Codium fragile

Codium fragile ssp. tomentosoides
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Photo Source: MIT Sea Grant College Program

Rhodophyta (Red Algae)

Bonnemaisonia hamifera
Common Name: Red Alga
This bright pink or red alga has small, hook-like appendages arising from its branches. It attaches to rocks and shells, and is most prominent seasonally, and appears to be restricted by cold climates.

Bonnemaisonia hamifera Bonnemaisonia hamifera.
Click image for full size.
Image used with permission of:
National University of Ireland, Galway, Seaweed Site.

Grateloupia turuturu
Common Name: Red Alga
This red algae can grow four to five feet tall. It has been introduced from Japan to the North Atlantic (mainly Rhode Island) and England. It can block sunlight to other organisms and reproduces fairly easily.

Lomentaria clavellosa
Common Name: Red Alga
This alga can grow up to 15.75 inches (40 cm) and has a hollow main stalk, which is soft and gelatinous. It is bright to dark red in color and is found in shallow waters, occasionally on mussels or other seaweeds.

Lomentaria orcadensis
Common Name: Red Alga
No information has been entered for this species.

Neosiphonia harveyi
Common Name: Filamentous Red Alga
Neosiphonia is a bushy red alga growing up to 16 inches (40.5 cm) that most likely originated in Japan. Its current range is from Newfoundland to South Carolina. It is a weedy, fouling species associated with boating and aquaculture.

Porifera (Sponges)

Halichondria bowerbankia sp.
Common Name: Bread-Crumb Sponge
This spong usually forms colonies south of Cape Cod. It has a wide variety of colors and may be brown, yellow, olive green, or bronze. Older colonies have finger-like 8mm projections. Colonies will form on rocks, algae, and pilings in the intertidal and below zones.

Cnidaria (Hydroids (Anemone-like Animals), Anemones, and Jellyfish)


Cordylophora caspia
Common Name: Colonial Hydroid
This light brown hydroid colony can grow up to 10 cm and lives in fresh to brackish (0-20 psu salinity) waters. Global distribution has expanded, presumably due to increased boat travel and ballast water exchange. Cordylophora alters community structure, and negatively affects populations of ciliates and bryozoans, while attracting barnacles, amphipods, and polycheates. Cordylophora has also become a problem for power plants and irrigation systems by clogging pipes and filters.

Garveia franciscana
Common Name: Hydroid
First identified in 1902, it has only recently been found in New England. Its ecological impact includes: competition, habitat change, and predation. Its economic impact includes: water-pump failures, increase in cleaning frequency at inlets, and decreasing efficiency of deoxygenating towers.


Diadumene lineata
Common Name: Orange Striped Green Anemone
The Striped Anemone has 50-60 tentacles, displays orange or white stripes against a greenish body, and can grow up to 1.5 inches (<4 cm). It was introduced from the Pacific, and has established itself from Massachusetts to Florida. It lives attached to hard surfaces in protected areas of the subtidal zone.

Diadumene lineata Diadumene lineata.
Click image for full size.
Image used with permission of Bishop Museum and University of Hawaii.

Sagartia elegans
Common Name: Purple Anemone
With up to 200 purple or pinkish tentacles, the Purple Anemone can grow up to 8 inches (roughly 20 cm). It lives in the subtidal zone up to 30 ft (9 m) deep, in protected areas. It was introduced from Europe. This anemone is difficult to find during the winter, but regrows at the single location in Massachusetts where it was first observed in warmer weather.

Sagartia elegans Sagartia elegans
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Photo source: J. Pederson, MIT Sea Grant College Program

Polychaeta (Segmented Worms)

Information and descriptions from Marine Polychaete Worms of the New England Region by Marian H. Pettibone, 1963 and A Practical Guide to the Marine Animals of Northeastern North America by Leland Pollack (1997).

Janua pagenstecheri (formerly known as Spirobus pagenstecheri)
Common Name: Polychaete
This is a relatively small polychaete that lives in a spiral calcareous tube. This is a very obscure species and there is relatively little information to provide. Its earlier identification was corrected by Marian Pettibone in a 1982 publication.


Nudibranchia (Sea slugs)

Thecacera pennigera
Common Name: Sea Slug
Originally found in the Atlantic coast of Europe, it is now seen in Africa, the Middle east, Japan, Brazil, and Australia. It's size ranges from is usually 15mm to 30mm long. Its color is usually a spotted, brown and orange appearance.

Thececera pennigera Thececera pennigera
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Photo source: D. Woods, A. Shepard, and C. Ranney

Gastropoda (Snails)

Littorina littorea
Common Name: Common Periwinkle Snail
This snail's shell is usually dark. It has transverse black stripes on its tentacles with structures on the whorls. It was introduced from Europe and has spread between Labrador and Virginia. It prefers hard surfaces, estuarine waters, and can be found in the intertidal to subtidal depths.

Littorina littorea Littorina littorea
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Photo source: J. Pederson, MIT Sea Grant College Program

Bivalvia (Clams, Oysters and Mussels)

Ostrea edulis
Common Name: European Oyster
This oyster has a shell that is wider and rounder than its Virginian counterpart. It is a grayish white shell, slightly scalloped with white muscle scar (the native oyster has a distinct purple muscle scar). It can grow up to 8 inches (20 cm). It was introduced from Europe and has been seen from Maine to Rhode Island in estuarine habitats, in the intertidal and subtidal zones.

Ostrea edulis Ostrea edulis.
Click image for full size.
Image used with permission of Kelly Galway Oysters.


Mysidacea (Mysid shrimp)

Praunus flexuosus
Common Name: Mysid Shrimp
This small shrimp can grow up to only 0.75 inches (20 mm) and lives in the lower shore in pools and in shallow water, especially over sandy substrates.

Isopoda (Isopods - relatives of sow bugs)

Ianiropsis sp.
Common Name: Isopod
This species is a new introduction, although it probably has been in Massachusetts and Rhode Island for several years. It is not easy to identify from available keys and we know very little about its habitat preferences, life history, and interaction with native species.

Amphipoda (Amphipods - relatives of sand fleas)

Caprella mutica
Common Name: Skeleton Shrimp
A large amphipod native to East Asia and Siberia that has been introduced to North America probably through either ballast water or through shipments of Japanese oysters. During the summer months it can be very abundant.

Microdeutopus gryllotalpa
Common Name: Amphipod
This amphipod is found in lagoons, salt marshes, among algae, shells, polzoans, tunicates etc., high detritus accumulation.

Cirripedia (Barnacles)

Chthamalus fragilis
Common Name: Barnacle
Gray, beige or brown in color it can grow up to 1cm in dimeter. It is common on south Cape Cod where it lives on rocks and other hard surfaces at high-tide levels.

Decapoda (Crabs and lobsters)

Carcinus maenas
Common Name: European Green Crab
This crab can have a somewhat variable colored carapace (shell), but is usually green, reddish orange, or tan, with darker mottling. It has 5 marginal teeth and can grow up to 3.6 inches (7.6 cm). It was introduced from Europe and has been spotted from Gulf of St.Lawrence to Delaware along hard and soft surfaces, in both intertidal and subtidal zones.

Carcinus maenas Carcinus maenas
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Photo source: P. Erickson for MIT Sea Grant College Program

Hemigrapsus sanguineus
Common Name: Asian Shore Crab
The Asian Shore Crab can readily be distinguished by its banded legs, red spots on the claws, and general square shape. It is much smaller than the European Green Crab, and only grows up to 1 inch (2.5 cm). Originally introduced from Asia, it now ranges from Maine to North Carolina, preferring rocky cobble floors in the intertidal and subtidal zones.

Hemigrapsus sanguineus Hemigrapsus sanguineus
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Photo source: P. Erickson for MIT Sea Grant College Program

Insecta (Insects)

Anisolabis maritima
Common Name: Maritime Earwig
The earwig is brownish to black and up to 20mm in size. It is common on the shore under rocks. It is distinguished by its 24 segments, antennae, and lack of wings.

Anisolabis maritima Anisolabis maritima
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Image used with permission of: Katsuyuki. Kohno

Bryozoa (Ectoprocta)

Alcyonidium sp.
Common Name:
No information has been entered for this species.

Barentsia benedeni
Common Name: Entoproct
An Entoproct with creeping growth composed of 5-10 stalks. It is tolerant of pollution and usually grows on piers and harbors pilings in sheltered bays and estuaries.

Bugula neritina
Common Name: Bryozoan
This bryozoan has flexible, bushy colonies, purplish to purplish brown in color, and can grow up to 4 inches (10 cm). Found in harbors and estuaries, it attaches itself to hard substrata. Much biochemical research has been conducted on this species as a source of bryostatin, a compound shown to be effective against leukemia.

Membranipora membranacea
Common Name: Lacy Crust Bryozoan
A white, lacy bryozoan, often found growing on kelp and other types of algae, has been found to have negative impacts on many Gulf of Maine ecosystems, including devastation of kelp forests. It first appeared at the Isle of Shoals, New Hampshire and Maine.

Tunicata: Ascidiacea (Tunicates)

Ascidiella aspersa
Common Name: Tunicate
This tunicate, growing to about 3-4 inches (8-10 cm). It attaches on one side to docks, rocks and other substrata. It is grayish to whitish, with pink tinges, and has a rigid, bumpy surface. It was introduced from Europe and has spread through Massachusetts to Connecticut.

Ascidiella aspersa Ascidiella aspersa
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Photo source: J. Pederson, MIT Sea Grant College Program

Botrylloides violaceus
Common Name: Tunicate
These colonies are composed of zooids arranged in loose circles, rows, or dense clusters. Coloration may vary between bright orange to reddish or dull purple. Since being introduced from the Pacific, Botrylloides has been found from Maine to Virginia along protected areas within the shallow subtidal zone.

Botrylloides violaceus Botrylloides violaceus
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Photo Source: P. Erickson for MIT Sea Grant College Program

Botryllus schlosseri
Common Name: Golden Star Tunicate
These small zooids are less than a tenth of an inch big and have white or yellow markings. They are colonial, and form a star-like appearance, which, as a colony can be up to 3-4 inches (7.5 - 10 cm). They have been introduced from Europe and have expanded from Newfoundland to the Chesapeake Bay, and can be found attached to docks or other hard substrates in protected areas of the subtidal, out to 60 feet deep.

Botryllus schlosseri Botryllus schlosseri
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Photo Source: MIT Sea Grant College Program

Didemnum sp.
Common Name: Tunicate
This tunicate has cream to white coloration with microscopic individual zooids. The large colonies are gritty and have hanging lobes attached. Overall, colonies may reach 12-18 inches (30-46 cm) long. This species may have been introduced from the Pacific or Europe, and now ranges from Maine to Connecticut. Most recently it has been found offshore, on Georges Bank. It attaches to or hangs off rocks, docks, and pilings and can be found in protected subtidal areas.

Didemnum Didemnum lahillei
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Photo source: USGS Woods Hole Science Center

Diplosoma listerianum
Common Name: Tunicate
A smooth, encrusting colony with a grayish tinge often has small white spots and can grow to 8 inches (20 cm). Native to northern Europe. Thus far, it has invaded from New Hampshire to Connecticut, remaining near shore, in protected areas, attached to docks, other organisms and hard surfaces.

Diplosoma listerianum Diplosoma listerianum
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Photo source: R. Whitlatch, University of Connecticut

Molgula manhattensis
Common Name: Sea Grapes
This solitary tunicate grows to about 5.0 cm and is grayish green although the tunic or outer covering is often covered with mud and hairs. It can be locally abundant and is pollution tolerant. It ranges from Maine to Louisiana.

Molgula manhattensis Molgula manhattensis
Photo Source: J. Pederson, MIT Sea Grant College Program

Styela canopus (formerly Styela partita)
Common Name: Rough Sea Tunicate
This tunicate or sea squirt arrived from the Pacific around 1852. It has a rough, leathery, reddish tunic, is about 1 inch long, and is found in southern New England. It probably arrived by ship fouling.

Styela clava
Common Name: Club tunicate
This stalked tunicate was introduced from Japan, can grow to about 6 inches long, and has been observed from Maine to New Jersey. It is found in shallow subtidal waters attached to docks within protected areas. It recently invaded Prince Edward Island and is fouling mussel aquaculture ropes.

Styela clava Styela clava
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Photo source: J. Pederson, MIT Sea Grant College Program

Click here for Cryptogenic species descriptions.
Click here to return to the intro page.

Note: The descriptions provided on this page are the most accurate available to us.  We would appreciate any new or updated information, or corrections that you may have.  We welcome your comments and suggestions as we continue to develop this site.


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  this page last updated on: 6 March, 2009