Invasion History

First Non-native North American Tidal Record: 1996
First Non-native West Coast Tidal Record: 1996
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Philine orientalis is native to the Western Pacific from Russia (Sea of Japan coast), Japan, China and south to the Gulf of Thailand, the Straits of Malacca, Java, and the Philippines (Golikov et al. 1976; Price et al. 2011). It was collected in Bodega Harbor, California in 1998, and later found in Tomales and San Francisco Bays (Michelle Chow, in Rudman 1999; Behrens 2004; Krug et al. 2012; California Academy of Sciences 2014).

North American Invasion History:

Invasion History on the West Coast:

Philine orientalis was first collected on the West Coast in Bodega Harbor, California in 1998. The discovery of P. orientalis occurred nearly simultaneously with the invasion of the New Zealand Sea Slug (P. auriformis), causing considerable confusion, which was increased by the muddled taxonomy of the genus. At one time, four species of introduced Philine: P. aperta, P. japonica, P. orientalis, and P. auriformis were listed for California waters (Behrens 2004). However, molecular and morphological analysis synonymized P. orientalis and P. japonica, and identified California P. aperta specimens as P. orientalis (Price et al. 2011; Krug et al. 2012). A graduate student, Michelle Chow, began studies of P. auriformis in Bodega Bay and found that at least two morphologically different species were present (Chow, in Rudman 1998-2014). By 2004, P. orientalis was collected in Tomales and San Francisco Bays (Behrens 2004; Krug et al. 2012). Within San Francisco Bay, P. orientalis, appears to be widely distributed, occurring in San Pablo Bay and the South Bay (Krug et al. 2012; California Academy of Sciences 2014). Although P. orientalis was first recognized in Bodega Harbor, as distinct from P. auriformis, it was most likely introduced to San Francisco Bay first, in ballast water, and then dispersed to Bodega and Tomales Bays. Philine spp. populations appeared to be ephemeral in Bodega and Tomales Bays in 2006-2010, and were not found some years. They were more stable in San Francisco and San Pablo Bays (Newsom and Williams 2014).


Philine orientalis is a sea-slug with an internal shell, known as a bubble-shell. It has a well-developed head-shield, which is wedge-shaped, but rounded anteriorly, and comprising about 2/3 of the body length. The parapodial lobes are thick and muscular. The notch may be present or absent on the anterior end of the head shield. The posterior end of the body is rounded when the gills are extended and squarish when the gills are partially contracted. The posterior shield is short and roughly quadrangular, ending in two posterior lobes. Three gizzard plates are visible through the dorsal and ventral surfaces of the body. The shell occupies most of the body cavity immediately ventral to the dorsal portion of the posterior shield. The shell is loosely or tightly coiled, and its surface can be smooth or dotted. The buccal organ is small, but muscular with the radular sac forming a postero-ventral lobe. The gizzard contains three similar calcareous spindle-shaped plates, which are convex on the ventral surface. The two paired plates fill most of the front end of the animal. Adult slugs are 25-40 mm in length. The body is translucent white. The shell is visible through the posterior tissue of the dorsal shield. Hancock's organs (i.e. paired chemosensory organs situated between the foot and the head-shield) are reddish brown, and consist of 12 simple folds. Description based on Behrens (2004), Gosliner and Williams (in Carlton 2007), Rudman 2009, and Price et al. (2011).

When exotic Philine sp. invaded California waters, there was confusion over their identity. At one time, four species of introduced Philine: P. aperta, P. japonica, P. orientalis, and P. auriformis were listed for California waters (Behrens 2004). A recent molecular analysis has reduced the crowd to two, P. auriformis and P. orientalis (Krug et al. 2012).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Opisthobranchia
Order:   Cephalaspidea
Family:   Philinidae
Genus:   Philine
Species:   orientalis


Philine japonica (Lischke, 1872)
Philine argentata (Gould, 1859)
Philine striatella (Tapperone-Canefri, 1874)

Potentially Misidentified Species

Philine aperta
Philine aperta Linneaus 1767 is native to the Atlantic coast of South Africa. This slug was erroneously reported to be present on the California coast (Behrens 2004; Krug et al. 2012). It was also lumped with the European species, P. quadripartita in the 20th century, and given a range from Britain to South Africa (Price et al. 2011).

Philine auriformis
Philine auriformis, native to New Zealand, is introduced and established on the California Coast in San Francisco, Tomales, and Bodega Bays (Price et al. 2011; Krug et al. 2012).



Philine orientalis is a sea-slug which inhabits sandy substrates, mudflats, and eelgrass beds (Golikov et al. 1976; Behrens 2004; California Academy of Sciences 2007). The animals are hermaphroditic and apparently do not self-fertilize. Fertilization is internal, and the individual lays ovoid egg masses, composed of spirals of capsules, each containing two eggs, and attached to the substrate by a mucous thread (Gosliner 1995; Behrens 2004). The eggs hatch into veligers, which lack yolk, and are likely planktotrophic.

Temperature and salinity tolerances of P. orientalis are not known, but its native and introduced range runs from warm- to cold-temperate climates. In San Francisco Bay, it ranges into San Pablo Bay, within the polyhaline zone (18-30 PSU). The slug's habitat ranges from the lower intertidal to depths as deep as 180 m, on silty to sandy bottoms. It does occur in eelgrass beds (Price et al. 2011; California Academy of Sciences 2014). On the Pacific coast of Russia, it is often associated with scallops (Golikov et al. 1976). Philine orientalis is a carnivore and feeds primarily on small bivalves. In Hong Kong, major prey items were juveniles of Venerupis philippinarum (Morton and Chiu 1990). This slug has a muscular buccal mass and a gizzard with calcareous plates for crushing shells (Morton 1990). Glands in the mantle of Philine spp. secrete noxious acid compounds which discourage predators (Cadien and Ranasinghe 2003).



Trophic Status:




General HabitatUnstructured BottomNone
General HabitatGrass BedNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEndobenthicNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Length (mm)25Behrens 2004; Price et al. 2011
Maximum Length (mm)40Behrens 2004; Price et al. 2011
Broad Temperature RangeNoneCold temperate-Tropical

General Impacts

In its native range, P. orientalis is a significant predator on small bivalves, including juveniles of the commercially important Venerupis philippinarum (Japanese Littlenecks) (Morton and Chiu 1990). Philine orientalis secretes a highly acidic mucus which can discourage feeding by other predators such as the native Dungeness Crab (Metacarcinus magister) and the introduced Green Crab (Carcinus maenas). This effect was found to reduce foraging rates by these predators in laboratory experiments but was not seen in field experiments in San Francisco Bay. Modeling suggested that interference would only occur under specific abundance levels of P. orientalis (Newsom and Williams 2014).

Regional Impacts

P112_CDA_P112 (Bodega Bay)Ecological ImpactCompetition
Under some conditions Philine orientalis interfered with predation on small clams by Dungeness Crabs (Metacarcinus magister) and Green Crabs (Carcinus maenas), but only when both crab species were present, and only at certain levels of density of the three predators (Newsom and Williams 2014).
P112_CDA_P112 (Bodega Bay)Ecological ImpactPredation
Phiiline orientalis was a significant predator on small bivalves in Bodega Harbor, CA (Newsom and Williams 2014).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-V Northern California to Mid Channel Islands 1996 Def Estab
EAS-I None 0 Native Estab
NWP-2 None 0 Native Estab
EAS-IV None 0 Native Estab
P112 _CDA_P112 (Bodega Bay) 1998 Def Estab
P090 San Francisco Bay 2004 Def Estab
P110 Tomales Bay 2004 Def Estab
NWP-3a None 0 Native Estab
EAS-VI None 0 Native Estab
NWP-4a None 0 Native Estab
NWP-3b None 0 Native Estab
EAS-II None 0 Native Estab
P130 Humboldt Bay 2015 Def Estab
NEP-IV Puget Sound to Northern California 2015 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
29053 Foss 2009 2005 2005-09-07 Redwood Creek - Shipping Def 37.5120 -122.2109
29412 Foss 2009 2005 2005-09-07 Dumbarton Bridge Def 37.5070 -122.1168
29755 California Academy of Sciences 2014 1996 1996-01-01 Bodega Harbor Def 38.3262 -123.0495
32636 Foss 2011 2010 2010-06-12 China Camp Def 38.0025 -122.4617
33116 Foss 2009 2005 2005-06-08 Crown Beach Def 37.7603 -122.2737


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