Invasion History

First Non-native North American Tidal Record: 1994
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1994

General Invasion History:

Favorinus auritulus was described from the state of Sao Paulo, Brazil (Marcus 1955). Subsequently, it was collected from Barbados, Curacao, Belize, Jamaica, Bermuda, and southern Florida, from Miami to the Indian River Lagoon (Edmunds 1964; Marcus and Marcus 1970; Marcus and Hughes 1974; Clark 1984; Clark 1995). One specimen of Favorinus sp. was identified by Terence Gosliner from fouling plates in lower Chesapeake Bay in 1994. Several similar nudibranchs were seen in later plates, but have not been definitively identified. The establishment of this tropical nudibranch in Chesapeake Bay is uncertain.

North American Invasion History:

Invasion History on the East Coast:

One specimen of a nudibranch, identified as Favorinus auritulus by Terence Gosliner, was collected from a fouling plate at Coast Guard Pier in Norfolk Harbor, Virginia in 1994 (Ruiz et al. unpublished data). Several additional specimens have been tentatively identified, but not confirmed. The range and degree of establishment of Favorinus auritulus in Chesapeake Bay is unknown. The absence of this nudibranch in Marcus' (1972) and Vogel's (1977) studies suggests that it is probably a recent introduction to the Chesapeake.


The body of Favorinus sp. is long and narrow, and tapers towards a long pointed tail. It has a maximum width of about a seventh to a fifth of its length. The front corners of the foot form short horns, curved backwards. The oral tentacles are longer than the rhinophores, and are about a quarter of the body length. The rhinophores bear 1 to 3 swellings along their length, with their number increasing with the animal's size. The rhinophores and oral tentacles are often brown from the base to a varying height, but the tips are white. The cerata are carrot-shaped and smooth, and in 2-6 groups (of varying number) along the animal's length. The first group has 8-15 cerata, the second 6-11, and the posterior groups have fewer, decreasing to 1-2 in the hindmost. The medial-dorsal cerata are longest, about 3/8 of body length. The body is whitish but very transparent, and the liver, varying in color from pinkish to yellowish with brown spots, is visible inside. Opaque white patches are scattered over the body. Individuals are 3-12 mm long. This description is based on Marcus (1957); Edmunds (1964); and Clark (1984)'s description of Favorinus auritulus.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Opisthobranchia
Order:   Nudibranchia
Family:   Facelinidae
Genus:   Favorinus
Species:   sp.


Potentially Misidentified Species

Favorinus blianus
A Northeastern Atlantic species, once photographed in Narragansett Bay, Rhode Island.

Favorinus branchialis
A Northeastern Atlantic species, formerly considered conspecific with F. auritulus.



Favorinus auritulus is a nudibranch found in found in lagoons and sheltered marine habitats (Edmunds 1964; Clark 1995). Nudibranchs are simultaneous hermaphrodites, and copulate reciprocally or unilaterally. We do not have information on this animal's egg masses or larval feeding mode. The similar F. branchialis lays its eggs in 'a delicate white spiral', containing up to 20,000 eggs (Thompson and Brown 1984).

Favorinus auritulus inhabits shallow shore habitats, including lagoons and cays. It is known from tropical and subtropical habitats from Brazil to Florida, presumably at full marine salinities. However, a specimen was found in Chesapeake Bay at 22 PSU (Ruiz et al., unpublished data), but it is not known whether they can tolerate the annual range of temperature and salinity there. It has been found on marine algae, such as Caulerpa, Penicllus, Sargssum and Padina (Marcus and Hughes 1974; Clark 1984). A frequent food is the egg masses of other opisthobranchs, which could include the eggs of herbivorous sea slugs (saccoglossans, cephalaspideans, aplysiids) (Edmunds 1964; Clark 1984). They have also been reported to feed on the bryozoan Zoobotryon verticllatum (Rudman 2014). In many nudibranchs which feed on cnidarians, the nematocysts (stinging cells) are ingested, and are then incorporated into the cerata, as a defensive mechanism (Barnes 1983). Favorinus branchialis does feed on hydroids in addition to opisthobranch egg (Thompson and Brown 1984), but we do not know whether Fzvorinus sp. does so.


nudibranch eggs; bryozoans

Trophic Status:




General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatCoral reefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Length (mm)12Marcus 1957; Clark 1984
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
SA-II None 1955 Native Estab
CAR-III None 0 Native Estab
CAR-IV None 0 Native Estab
CAR-II None 0 Native Estab
NA-ET4 Bermuda 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 1994 Def Unk
M130 Chesapeake Bay 1994 Def Unk
S200 Biscayne Bay 0 Native Estab
S196 _CDA_S196 (Cape Canaveral) 0 Native Estab
S190 Indian River 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abbott, R. Tucker (1974) American Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

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

Clark, Kerry B. (1984) New records and synonymies of Bermuda opisthobranchs (Gastropoda), Nautilus 98(2): 85-97

Clark, Kerry B. (1995) Rheophilic/oligotrophic lagoonal communities through the eyes of slugs (Mollusca: Opisthobranchia), Bulletin of Marine Science 57(1): 242-251

Edmunds, Malcolm (1964) Eolid mollusca from Jamaica, with descriptions of two new genera and three new species., Bulletin of Marine Science of the Gulf and Caribbean 14(1): 1-32

Edmunds, Malcolm; Marcus, Eveline Du Bois (1977) On Favorinus auritulus (Marcus) and Favorinus branchialis (Muller), Journal of Molluscan Studies 43: 200-201

Marcus, Ernesto (1955) Opisthobranchia from Brazil., Boletin da Faculdade de Filosofia, Ciências e Letras da Universidade de Sao Paulo, Zoologia 20: 89-262

Marcus, Ernst, Marcus; Eveline d.B.R. (1970) Opisthobranchs from Curacao and faunistically related regions, Studies on the Fauna of Curacao and Other Caribbean Islands 122: 1-129

Marcus, Eveline du Bois Reymond (1972) Notes on some opisthobranch gastropods from the Chesapeake Bay, Chesapeake Science 13(4): 300-317

Marcus, Eveline du Bois-Reymond; Hughes, Helen P. (1974) Opisthobranch mollusks from Barbados, Bulletin of Marine Science 24(3): 498-532

Rosenberg, Gary 1995-2023 Malacolog 4.1.

Rudman, W. B. 1997-2016 Sea Slug Forum.

Thompson, T. E. (1980) Jamaican opisthobranch molluscs., Journal of Molluscan Studies 46: 74-99

Thompson, T. E.; Brown, G. H. (1984) <missing title>, Ray Society, London. Pp. <missing location>

Vogel, Rosalie M. (1977) <missing title>, M.S. Thesis, College of William and Mary, Williamsburg, VA.. Pp. <missing location>