Invasion History

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

General Invasion History:

Microcosmus exasperatus was described by Heller from the West Indies or northern South America in 1876 (Van Name 1921; Van Name 1945). However, it is widely distributed in the tropical Atlantic and Indo-Pacific and is cryptogenic over this range. It is considered introduced in the Mediterranean (Amor et al. 2016; Turon et al. 2007; Ramos-Espla et al. 2013), Northwest Africa (Monniot and Monniot 1994), Pacific Islands (Guam, Lambert 2002; Lambert 2003, Hawaii, Monniot 1981; and the Galapagos (Lambert 2019). In 2009, it was collected at the Pacific entrance to the Panama Canal (Carman et al. 2011).

North American Invasion History:

Invasion History Elsewhere in the World:

Microcosmus exasperatus is considered cryptogenic in the eastern and western tropical Atlantic, and in the Indo-West Pacific but is introduced in the central and eastern Mediterranean, and Pacific oceanic islands. The invasion of M. exasperatus was complicated by the invasion of its Indo-Pacific congener, M. squamiger, which has invaded much of the western Mediterranean (Shenkar and Loya 2009; Ramos and Espla 2013). The earliest record of M. exasperates was on the Western Djerba Island. Tunisia, in the Gulf of Gabes in 1998. Later records were on the coast of Israel (2002), and Beirut, Lebanon (2004), and Alsancak Harbour, Turkey, on the Aegean Sea (2004) (Shenkar and Loya 2009; Ramos and Espla 2013). Microcosmus exasperatus is considered a likely Lessepsian species, which probably colonized the Mediterranean through the Suez Canal (Shenkar and Loya 2009; Ramos and Espla 2013).


Microcosmus exasperatus is a solitary tunicate, but usually occurs in dense clumps or aggregates. The body is ovate, but irregular, attached by a large area on the posterior ventral side. The test is rough, and leathery. Apertures are usually located on short, wart-like siphons about a third of the body length and are directed away from each other. However, sometimes the oral siphon is terminal with a long straight siphon, while the atrial siphon is short and about half-way along the body. Large specimens reach about 55 mm. The color vaires from reddish-brown to purple, with pink or bright-orange siphons (Van Name 1945; Kott 1985; Goodbody and Webber 2003).

This species is frequently confused with the very similar species Microcosmus squamiger (Mastrototaro and Dappiano 2005; Turon et al. 2007). One of the few characteristics used to distinguish between the two species is the shape of the internal siphonal spines. The spines of M. squamiger are very short, about 15-25 µm long, and shaped like fingernails with serrated rims, while M. exasperatus has longer pointed spines, about 40-50 µm long, which are posteriorly hooked (Kott, 1985; Mastrototaro and Dappiano 2005).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Stolidobranchia
Family:   Pyuridae
Genus:   Microcosmus
Species:   exasperatus


Microcosmus biconvolutus (Sluiter, 1898)
Microcosmus distans (Heller, 1878)
Microcosmus haemisphaerium (Sluiter, 1904)
Microcosmus miniatus (Verrill, 1900)
Microcosmus variegatus (Heller, 1878)
Microscosmus claudicans var. australis (Hartmeyer and Michaelsen, 1928)
Ascidia cavernosa (Leseur, 1823)
Ascidia variabilis (Leseur, 1823)
Microcosmus anchylodeirus (Traustedt, 1883)
Pyura cavernosa (Hartmeyer, 1911)
Pyura variabilis (Hartmeyer, 1911)

Potentially Misidentified Species

Microcosmus squamiger
Microcosmus squamiger is native to the Indo-Pacific, but is widely introduced, in the Western Mediterranean, Azores, South Africa, and California and Mexico.



Life History- A solitary tunicate is ovoid, elongate or vase-like in shape, with two openings or siphons. Most solitary tunicates attach to substrates by their side or base, but some attach with a conspicuous stalk. They are sessile filter feeders with two siphons, an oral and an atrial siphon. Water is pumped in through the oral siphon, where phytoplankton and detritus is filtered by the gills, and passed on mucus strings to the stomach and intestines. Waste is then expelled in the outgoing atrial water.

Solitary ascidians are hermaphroditic, meaning that both eggs and sperm are released to the atrial chamber. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but many species have a partial block to self-fertilization. Depending on the species, eggs may be externally or internally fertilized. In external fertilizers, eggs and sperm are released through the atrial siphon into the surrounding water column were fertilization takes place. In internal fertilizers, eggs are brooded and fertilized within the atrial chamber and then released into the water column upon hatching. Fertilized eggs hatch into a tadpole larva with a muscular tail, notochord, eyespots, and a set of adhesive papillae. The lecithotrophic (non-feeding, yolk-dependent) larva swims briefly before settlement. Swimming periods are usually less than a day and some larvae settle immediately after release, but the larval period can be longer at lower temperatures. Once settled, the tail is absorbed, the gill basket expands, and the tunicate begins to feed by filtering (Barnes 1983).

Microcosmus exasperatus is widespread in subtropical and tropical marine waters at polyhaline to euhaline salinities (Van Name 1945; Nagar and Shenkar 2016). It has been found on a wide range of substrates on pilings, stones, mangrove roots, and coral reefs, buoys, floats, and vessel hulls (Van Name 1945; Woods Hole Oceanographic Institution 1952; Godwin 2002).



Trophic Status:

Suspension Feeder



General HabitatMarinas & DocksNone
General HabitatCoral reefNone
General HabitatMangrovesNone
General HabitatRockyNone
General HabitatVessel HullNone
General HabitatOyster ReefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatLittoralNone

Life History

Tolerances and Life History Parameters

Minimum Temperature (ºC)12Experimental (Nagar and Shenkar 2016)
Maximum Temperature (ºC)30Experimental (Nagar and Shenkar 2016)
Minimum Salinity (‰)24Field (Brazil, Marins et al. 2010); 33 PSU (Experimental, Israel, Nagar and Shenkar 2016)
Maximum Salinity (‰)45Experimental (Nagar and Shenkar 2016)
Minimum Length (mm)55Van Name 1945
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Microcosmus exaspenratus is a widespread and common fouling organism on buoys, pilings, vessel hulls, oil platforms, and cultured bivalves (Woods Hole Oceanographic Institution 1952; Godwin 3009; da Rocha et al. 2009). However, specific impacts are unknown.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
SP-XXI None 1940 Def Estab
CAR-II None 1878 Crypto Estab
CAR-VII Cape Hatteras to Mid-East Florida 1885 Crypto Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1884 Crypto Estab
NA-ET4 Bermuda 1900 Crypto Estab
SA-II None 1925 Crypto Estab
WA-IV None 1955 Crypto Estab
WA-V None 1955 Crypto Estab
EA-V None 0 Crypto Estab
EA-III None 1908 Crypto Estab
RS-1 None 1918 Crypto Estab
RS-2 None 1918 Crypto Estab
RS-3 None 1918 Crypto Estab
NWP-2 None 0 Crypto Estab
EAS-III None 0 Crypto Estab
EAS-I None 0 Crypto Estab
SP-IV None 0 Crypto Estab
SP-XII None 1949 Def Estab
SP-V None 0 Crypto Estab
MED-IV None 1998 Def Estab
CAR-IV None 1878 Crypto Estab
CAR-III None 1884 Crypto Estab
AUS-I None 0 Crypto Estab
AUS-II None 0 Crypto Estab
AUS-VIII None 0 Crypto Estab
AUS-III None 0 Crypto Estab
AUS-XII None 0 Crypto Estab
AUS-X None 1853 Crypto Estab
WA-I None 1963 Crypto Estab
SA-III None 2005 Crypto Estab
WA-II None 1965 Crypto Estab
MED-V None 2007 Def Estab
G040 Rookery Bay 1884 Crypto Estab
S206 _CDA_S206 (Vero Beach) 1884 Crypto Estab
CAR-II None 1884 Crypto Estab
CAR-III None 1884 Def Estab
S050 Cape Fear River 1885 Crypto Estab
SP-XI None 1951 Def Estab
NWP-3a None 0 Crypto Estab
G060 Sarasota Bay 1952 Crypto Estab
G045 _CDA_G045 (Big Cypress Swamp) 1983 Crypto Estab
G010 Florida Bay 1982 Crypto Estab
AUS-IV None 0 Crypto Estab
SEP-H None 2008 Def Estab
CIO-II None 2004 Crypto Estab
CIO-I None 2004 Crypto Estab
SA-IV None 0 Crypto Estab
SP-VII None 0 Crypto Estab
S190 Indian River 0 Crypto Estab
PAN_PAC Panama Pacific Coast 2009 Def Estab
PAN_CAR Panama Caribbean Coast 0 Crypto Estab
SEP-Z None 2016 Def Unk
MED-VI None 2004 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abdul, Jaffar Ali H.; Sivakumar, V. (2007) Occurrence and distribution of ascidians in Vizhinjam Bay (south west coast of India)., Journal of Experimental Marine Biology and Ecology 342: 189-190

Ali, H. Abdul Jaffar; Sivakumar, V.; Tamilselvi, M. (2009) Distribution of alien and cryptogenic ascidians along the southern coasts of Indian peninsula, World Journal of Fish and Marine Sciences 1(4): 305-312

Amor, Kounofi-Ben; Rifi, M.; Ghanem, R.; Draief, I.; Zouali, J.; Souissi, J. Ben (2016) Update of alien fauna and new records of Tunisian marine fauna, Mediterranean Marine Science 17(1): 124-143

Berrill, N. J. (1932) Ascidians of the Bermudas, Biological Bulletin 62(1): 77-88

Caraballo-Pérez, Virginia; Díaz, Oscar (2011) [Tunicates (Tunicata: Ascidiacea) of the Gulf of Cariaco, Venezuela], Boletino del Instituto Oceanographico de Venezuela 50(2): 233-244

Carlton, James T.; Eldredge, Lucius (2009) Marine bioinvasions of Hawaii: The introduced and cryptogenic marine and estuarine animals and plants of the Hawaiian archipelago., Bishop Museum Bulletin in Cultural and Environmental Studies 4: 1-202

Carman, Mary R. and 7 authors 2010 Ascidians at the Pacific and Atlantic entrances to the Panama Canal. <missing URL>

Carman, Mary, and 8 authors (2011) Ascidians at the Pacific and Atlantic entrances to the Panama Canal, Aquatic Invasions 6(4): 371-380

Cole, Linda; Vorontsova, Maria (1998) Species of Pyuridae (Ascidiacea) from South Vietnam, Bulletin of Marine Science 62(1): 1-6

Coles S. L., DeFelice R. C., Eldredge, L. G. (1999a) Nonindigenous marine species introductions in the harbors of the south and west shores of Oahu, Hawaii., Bishop Museum Technical Report 15: 1-212

Coles, S. L.; DeFelice, R. C.; Eldredge, L. G.; Carlton, J. T. (1999b) Historical and recent introductions of non-indigenous marine species into Pearl Harbor, Oahu, Hawaiian Islands., Marine Biology 135(1): 147-158

Coles, S. L.; DeFelice, R. C.; Minton, D. (2001) Marine species survey of Johnston Atoll, Central Pacific Ocean, June 2000, Bishop Museum Technical Report 19: 1-59

da Rocha, Rosa Morales and 13 authors (2010) Inventory of ascidians (Tunicata, Ascidiacea) from the National Park La Restinga, Isla Margarita, Venezuela, Biota Neotropica 10: published online

da Rocha, Rosana M.; Costa, Luciana (2005) Ascidians (Urochordata: Ascidiacea) from Arriaal do Cabo, Rio de Janeiro, Brazil., Iheringia Series Zoologie 95(1): 57-64

da Rocha, Rosana M.; Faria, Suzana B.; Moreno, Tatiane R. (2005) Ascidians from Bocas del Toro, Panama, Caribbean Journal of Science 41(3): 600-612

da Rocha, Rosana M.; Kremer, Laura P. (2005) Introduced ascidians in Paranagua Bay, Parana, southern Brazil., Revista Brasileira da Zoologia 22(4): 1170-1184

Dalby, James E. Jr.; Young, Craig M. (1992) Role of early post-settlement mortality in setting the upper depth limit of ascidians in Florida epifaunal communities, Marine Ecology Progress Series 80: 221-228,

Dias, G. M.; Rocha, R. M.; Lotufo, T. M. C.; Kremer, L. P. (2013) Fifty years of ascidian biodiversity research in Sao Sebastiao, Brazil, Journal of the Marine Biological Association of the United Kingdom 93(1): 273-282

Godwin, Scott L. (2003) Hull fouling of maritime vessels as a pathway for marine species invasions to the Hawaiian Islands., Biofouling 19 (Suppl): 123-131

González-Sánchez, K.; Flores-Alvarado, B.; Montiel-Barrantes,P., Gómez-Arce, G.; Alvarado, J. J. (2021) Ascidian diversity of Costa Rica, including new records for the North Pacific, Revista de Biologia Tropical 69(Suppl. 2): S234-S245

Goodbody, Ivan; Webber, Mona (2003) <missing title>, 3 Environmental Foundation of Jamaica, Kingston. Pp. <missing location>

Granthom-Costa, Luciana Vieira; Werner Ferreira, Carlos Gustavo; Dias, Gustavo Muniz (2016) Biodiversity of ascidians in a heterogeneous bay from southeastern Brazil, Management of Biological Invasions 7: 5-12

Ignacio, Barbara L.; Julio, Luciana M.; Junqueira, Andrea O. R; Ferreira-Silva, Maria A. G. (2010) Bioinvasion in a Brazilian Bay: filling gaps in the knowledge of southwestern Atlantic biota, PLOS ONE 5(9): <missing location>

Kott, P. (2005) Catalogue of Tunicata in Australian waters, Queensland Museum, Brisbane. Pp. 1-301

Kott, Patricia (1985) The Australian Ascidiacea Part 1, Phlebobranchia and Stolidobranchia., Memoirs of the Queensland Museum 23: 1-440

Lambert, Gretchen (2002) Nonindigenous ascidians in tropical waters., Pacific Science 56(3): 191-298

Lambert, Gretchen (2003) Marine biodiversity of Guam: the Ascidiacea., Micronesica 35-36: 584-593

Lira, Simone Maria de Albuquerque ; Farrapeira, Cristiane Maria Rocha (2010) Sessile and sedentary macrofauna from the Pirapama Shipwreck, Pernambuco, Brazil, Biota Neotropica 10(4): published online

Marins, Flavia O.; Novaes, Roberto L. M.; Rocha, Rosana M.; Junquiera, Andrea O. R. (2010) Non indigenous ascidians in port and natural environments in a tropical Brazilian bay, Zoologia 27(2): 213-222

Mastrototaro, F.; Dappiano, M. (2005) New record of the non-indigenous species Microcosmus squamiger (Ascidiacea: Stolidobranchia) in the harbour of Salerno (Tyrrhenian Sea, Italy)., JMBA2- Biodiversity Records (online) online: <missing location>

Millar, R. H. (1958) Some ascidians from Brazil., Annals and Magazine of Natural History 13(1): 497-514

Monniot, C. (1981) Apparition de L'ascidie Microcosmus exasperatus dans les ports Mediterraneens., Tethys 10(1): 59-62

Monniot, Claude (1972) [Stolidobranch Ascidians of Bermuda[ (French), Bulletin du Museum National d'Histoire Naturelle. 4e Serie. Section A. Zoologie, Biologie et Ecologie Animales 43: 617-643

Monniot, Claude; Monniot, Francoise (1994) Additions to the inventory of Eastern tropical Atlantic Ascidians: arrival of cosmopolitan species., Bulletin of Marine Science 54(1): 71-93

Monniot, Claude; Monniot, Francoise; Griffiths, Charles; Schleyer, Michael (2001) South African Ascidians., Annals of the South African Museum 108(1): 1-141

Moura, Carlos J.; Collins, Allen G.; Santos, Ricardo S.; Lessios, Harilaos (2019) Predominant east to west colonizations across major oceanic barriers: Insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker, Ecology and Evolution 9: :13001–13016.
DOI: 10.1002/ece3.5608

Nagar, Lilach Raijman; Shenkar, Noa (2016) Temperature and salinity sensitivity of the invasive ascidian Microcosmus exasperatus Heller, 1878, Aquatic Invasions 11: In press

Oliveira Filho, R. R.; Lotufo, T. M. C.; 2010 New records of introduced ascidians at Ceara State harbors, Northern Brazil. <missing URL>

Quintanilla, Elena; Thomas Wilke; Ramırez-Portilla, Catalina; Sarmiento, Adriana; Sanchez, Juan A. () , None <missing volume>: <missing location>

Quintanilla, Elena; Thomas Wilke; Ramırez-Portilla, Catalina; Sarmiento, Adriana; Sanchez, Juan A.2017 (2017) Taking a detour: invasion of an octocoral into the Tropical Eastern Pacific, Biological Invasions <missing volume>(17): 2583–2597
DOI 10.1007/s10530-017-1469-2

Ramos-Espla, Alfonso A.; Izquierdo, Andres; Cinar, Melih Ertan (2013) Microcosmus exasperatus (Ascidiacea: Pyuridae), current distribution in the Mediterranean Sea, Marine Biodiversity Records 6: e89

Rocha, Rosana M.; Bonnet, Nadia Y. K.; Baptista, Mariah S.; Beltramin, Fabiele S. (2012) Introduced and native phlebobranch and stolidobranch solitary ascidians (Tunicata: Ascidiacea) around Salvador, Bahia, Brazil, Zoologia 29(1): 39-53

Shenkar, Noa; Loya, Yossi (2009) Non-indigenous ascidians (Chordata: Tunicata) along the Mediterranean coast of Israel, Marine Biodiversity Records 2: 1-7

Tamilselvi, M. ; Sivakumar, V.; Ali, H. Abdul Jaffar; Thilaga, R. D. (2011) Distribution of alien tunicates (ascidians) in Tuticorin coast, India, World Journal of Zoology 6(2): 164-172

Tokioka, Takasi (1967) Pacific Tunicata of the United States National Museum, United States National Museum Bulletin 251: 1-247

Turon, Xavier; Nishikawa, Teruaki; Rius, Marc (2007) Spread of Microcosmus squamiger (Ascidiacea: Pyuridae) in the Mediterranean Sea and adjacent waters., Journal of Experimental Marine Biology and Ecology 342: 185-188

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

Van Name, Willard G. (1921) Ascidians of the West Indian region and southeastern United States., Bulletin of the American Museum of Natural History 44: 283-494

Woods Hole Oceanographic Institution, United States Navy Dept. Bureau of Ships (1952) Marine fouling and its prevention., United States Naval Institute., Washington, D.C.. Pp. 165-206