Invasion HistoryFirst Non-native North American Tidal Record: 1980
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1980
General Invasion History:
Thecacera pennigera is a cosmopolitan species, described from southern England, but known from locations around the globe. It occurs in the Eastern Atlantic from Scotland to South Africa (Dekker 1986; Valles et al. 2000; Mead et al. 2011b); Brazil (Marcus 1957); the Arabian Sea (Eliot 1905, cited by Willan 1976); and the Western Pacific, from the Sea of Japan (Baba 1960) to Australia and New Zealand (Willan 1976; Burn 2006). It has not been reported from the Eastern Pacific, to our knowledge. At many of the sites where it has been collected, it appears to be rare and/or sporadic, often known from single specimens, or briefly abundant and then disappearing (Willan 1976; Dekker 1986; Clark 1995; Valles et al. 2000; Australian Museum 1998-2014). Thecacera pennigera feeds on bryozoans of the genus Bugula, which are abundant in ship fouling, and so, has great potential for ship transport. Although this sea slug was described from Europe, its origin is unknown. William Rudman (Australian Museum 1997) suggests the Western Pacific as a possibility. Occurrences of this conspicuous nudibranch in fairly well-studied areas of Australia in 1951 (Allan 1957, cited by Willan 1976), New Zealand in 1973 (Willan 1976), the eastern Mediterranean (Barchana, in Australian Museum 2006), Florida in 1972-1980 (Clark 1995; Goddard, in Australian Museum 2005), and Woods Hole, Massachusetts (Shepard, in Australian Museum 2003) are indicative of modern introductions.
North American Invasion History:
Invasion History on the East Coast:
Willan (1976) stated that there were no records of T. pennigera from North America. However, Kerry Clark collected this nudibranch at Sebastian Inlet, in the Indian River Lagoon, Florida between 1972 and 1980, but did not find it in later sampling (1985-1994) (Clark 1995). Thecacera pennigera was collected again at this location in 2005 (Goddard, in Australian Museum 2005). In 1981, two specimens were collected off Georgia and South Carolina, well offshore at depths of 28 and 33 m, unusual for this species (USNM 848877 and 848880, U.S. National Museum of Natural History 2014). In November 2003, T. pennigera appeared much farther north, in Woods Hole, Massachusetts (Alan Shepard, in Australian Museum 2003). It soon disappeared, but was found again 'in great numbers' in November 2006 (Alan Shepard, in Australian Museum 2006).
Invasion History Elsewhere in the World:
As described above, T. pennigera appears to be cryptogenic in much of its world wide range. Many of its occurrences are single specimens, or brief population 'booms', often near harbors, and very spotty geographically. In Australia, the first collection was in 1951, in Sydney Harbour (Allan 1957, cited by NIMPIS 2014), and subsequent collections have been in harbor areas [Adelaide, Port Philip Bay, and Port Stephens (Burn 2006; Australian Museum 1998-2014)]. New Zealand records are from two harbors on the North Island [Waitemata and Whangarei (Willan 1976; Australian Museum 1999)]. Scattered records are known from the Central and Eastern Mediterranean, from Italy (Vayssiere 1913, cited by Willan 1976; Cattaneo-Vietti & Chemello 1987, cited by Kapiris et al. 2014; Cattaneo-Vietti & Giovine 2008, cited by Kapiris et al. 2014) and Israel (in 2008, Dani Barchana, in Australian Museum 2008). These records are collections or sightings of single specimens, so the establishment of this species in the Mediterranean is unknown. The absence of records in the Western Mediterranean suggests that the central and eastern records are due to ship transport, either from the Eastern Atlantic, or by the Suez Canal.
Thecacera pennigera has a slender body, tapering to a long tail. Its foot is narrow, but projects slightly beyond the body. Below the head are two broad, pointed extensions. There are no oral tentacles. The rhinophores are club-like structures, each consisting of 14 lamellae, and are flanked anteriorly by a larger, leaf-like sheath. There are 3-5 gills on the dorsal midline, each consisting of smaller feathery structures. Behind the gills is a pair of cerata (simple, tapering structures). The tail is about half the body length. The whole animal reaches about 30 mm. Its body is translucent, but marked with conspicuous orange and black spots, which extend to the rhinophores, gills, and cerata. The color patterns are variable between individuals, but at least for European specimens, the orange sots are 'always' larger than the black ones, and the tops of the rhinophores are yellow, with black speckles. Description based on Willan (1976), Thompson and Brown (1984), Rudman (1997), Valles et al. (2000), and Jung et al. (2013).
Thecacera lamellata (Barnard, 1933)
Thecacera maculata (Eliot, 1905)
Potentially Misidentified Species
Thecacera pennigera is a nudibranch which inhabits harbors, inlets, and open coasts. Nudibranchs are simultaneous hermaphrodites and copulate reciprocally or unilaterally. Eggs are laid in masses forming a white, buff, or pink band (Thompson and Brown 1984; Shepard, in Australian Museum 2003). We have not found information on larval development of T. pennigera. Its reproductive mode is unknown. Dramatic population fluctuations seem to be common in nudibranchs, and T. pennigera seems to have brief blooms, followed by disappearances, and then reappearances years later at the same location (Sebastian Inlet, e.g. Clark 1995, Goddard, in Rudman 2014; Woods Hole, Shepard 2003, 2006, in Rudman 2014). This may indicate an ability to persist at very low densities.
Thecacera pennigera inhabits rocky areas, pilings, and soft bottoms with bryozoans. Its wide range indicates a broad tolerance of temperature from cold-temperate to tropical regions, but not much penetration into low salinities (Baba 1960c; Willan 1976; Dekker 1986; Thompson and Brown 1984; Rudman 1998-2014; Kapiris 2013). It feeds on bryozoans of the genus Bugula, on colonies attached to hard surfaces and algae. The association with Bugula has probably led to wide dispersal in ship fouling (Willan 1976; Thompson and Brown 1984; Mead et al. 2011b).
Bryozoans (Bugula spp.)
|General Habitat||Coarse Woody Debris||None|
|General Habitat||Marinas & Docks||None|
|Salinity Range||Polyhaline||18-30 PSU|
|Salinity Range||Euhaline||30-40 PSU|
Tolerances and Life History Parameters
|Maximum Length (mm)||30||Willan 1976; Thompson and Brown 1984|
|Broad Temperature Range||None||Cold Temperate-Tropical|
|Broad Salinity Range||None||Polyhaline-Euhaline|
General ImpactsNo impacts have been reported for this species.
Regional Distribution Map
|Bioregion||Region Name||Year||Invasion Status||Population Status|
|CAR-I||Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida||1980||Def||Estab|
|NA-ET3||Cape Cod to Cape Hatteras||2003||Def||Estab|
|CAR-VII||Cape Hatteras to Mid-East Florida||1981||Def||Unk|
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