Invasion History

First Non-native North American Tidal Record: 2016
First Non-native West Coast Tidal Record: 2016
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The nudibranch Dendronotus orientalis was described from Osaka Bay, Japan, where it was collected from the hydroid Ectopleura crocea (Baba 1932). Records of this slug were rare until 2002, when a number of records were reported to the online global Sea Slug Forum (Rudman 2017). Dendronotus orientalis has been found from the South China Sea in the Philippines, to Peter the Great Bay, Russia (Martynov 2014, cited by Marisa Agarwal 2017; Rudman 2017).

In March 2016, one individual D. orientalis was found by Robin Agarwal, diving in the harbor of Redwood City, California, on South San Francisco Bay. She posted the pictures on iNatualist (Robin Agarwal 2016), and it was quickly identified by Alison Young, Citizen Science Engagement Coordinator at the California Academy of Sciences (CAS).and confirmed by Rebecca Johnson, CAS Citizen Science Research Coordinator, Gary McDonald of the Long Marine Laboratory of the University of California Santa Cruz, and Jeffrey Goddard of the University of California Santa Barbara (Marisa Agarwal 2017). Twenty-two specimens, and probable egg masses, were found in April 2016. No specimens have been seen since April 2016, so establishment of this population is somewhat uncertain (Marisa Agarwal 2017). Ballast water and hull fouling are likely vectors for the introduction of this nudibranch.

North American Invasion History:


Dendronotus orientalis (Baba, 1932) has a broadly elliptical outline, tapered towards the rear. It bears numerous papillae, many of which are prominently branched or subdivided. A pair of short, stout tentacles at the anterior of the head are each divided into three long, tapering papillae, and a short, rudimentary papilla. The rhinophore sheath is short, with two stout, lateral papillae, and one long thin posterior papilla, which may extend up to twice the body length. The posterior papilla pass through the rhinophore itself, which is short and conical. There are four pairs of dorsal papillae, each bearing branchial leaflets, and decreasing in height from anterior to posterior. The body is translucent, with numerous small brown spots and thin yellow lines. Baba's preserved specimens were ~ 7 mm long, but live specimens are 20-35 mm in length. This description is based on: Baba 1932, Rudman 2002; Agarwal 2017.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Opisthobranchia
Order:   Nudibranchia
Family:   Dendronotidae
Genus:   Dendronotus
Species:   orientalis


Pseudobornella orientalis (Baba, 1932)
Dendronotus orientalis (Stout, 2011)

Potentially Misidentified Species

Dendronotus frondosus
Native, cosmopolitan in temperate waters, some similarity in color and morphology (Behrens 1991)

Dendronotus subramosus
Native, some similarity in color and morphology (Behrens 1991)



The nudibranch Dendronotus orientalis inhabits bays, harbors, and open coasts. Nudibranchs are simultaneous hermaphrodites and copulate reciprocally or unilaterally (Barnes 1983; Behrens 1984; Goddard 2007). In San Francisco Bay, D. orientalis laid globular egg masses on the hydroid Ectopleura crocea (Marisa Agarwal 2017). Most Northeast Pacific nudibranchs hatch out as planktotrophic larvae, but some have lecithotrophic larvae (Barnes 1983; Behrens 1984; Goddard 2007).

Dendronotus orientalis is known from rocky areas, eelgrass (Zostera sp) beds, sandy bottoms, and floating docks in harbors of warm-temperate to tropical regions in marine salinities (Baba 1932; Rudman 2002-2006; Robin Agarwal 2016; Marisa Agarwal 2017). It feeds on the hydroid Ectopleura crocea, and probably on other tubularian hydroids (Baba 1932; Rudman 2002-2006; Robin Agarwal 2016; Marisa Agarwal 2017).


Tubularia, Ectopleura spp.

Trophic Status:




General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatUnstructured BottomNone
General HabitatGrass BedNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Length (mm)10Song, in Rudman 2005
Maximum Length (mm)35Robin Agarwal 2017
Broad Temperature RangeNoneTropical-Warm Temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

No economic or ecological impacts have been reported for Dendronotus orientalis.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3b None 1932 Native Estab
NWP-3a None 0 Native Estab
EAS-III None 0 Native Estab
NWP-4a None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2016 Def Unk
P090 San Francisco Bay 2016 Def Estab
NWP-1 None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Agrawal, Robin 3/29/16 <em>Dendronotus orientalis</em> Observed by anudibranchmom March 29, 2016. confiming comments form Jeff Goddard and others

Baba, Kikutaro (1932) Pseudobornella orientalis nov. gen. et sp. from Japan, Annotationes Zoologiacae Japonenses 18(4): 369-376

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

Behrens, D.W. (1991) Pacific Coast Nudibranchs, In: (Eds.) . , Monterey, California. Pp. <missing location>

Pola, Marta; Gosliner, Terrence M. (2010) The first molecular phylogeny of cladobranchian opisthobranchs (Mollusca, Gastropoda, Nudibranchia), Molecular Phylogenetics and Evolution 56: 931-941

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

Stout, Carla C.; Wilson, Nerida G.; Valdés, Ángel (2011) A new species of deep-sea Dendronotus Alder & Hancock (Mollusca : Nudibranchia) from California, with an expanded phylogeny of the genus, Invertebrate Systematics 25: 60-69

Tan, Siong Kiat; Loh, Rebecca K.; Ng, Ting Hui (2021) First record of the worm snail Eualetes tulipa (Rousseau in Chenu, 1843) in Southeast Asia, BioInvasions Records 10(3): 605-611