Invasion History

First Non-native North American Tidal Record: 2001
First Non-native West Coast Tidal Record: 2001
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Myrianida pentadentata is a marine polychaete, described from the Seto Inland Sea, Japan (Imajima 1966b). The extent of its presumed native range in the Northwest Pacific is unknown. It has been collected from floats and ship hulls in San Diego Bay and Los Angeles Harbors, where it is presumed to be introduced (Nygren 2004; Nygren and Pleijel 2010).

North American Invasion History:

Invasion History on the West Coast:

Myrianida pentadentata was collected from hull fouling on a ship in Los Angeles Harbor, and from a floating dock in San Diego Harbor in 2001 (Nygren 2004). We consider this polychaete to be established on the West Coast. However, its abundance, and the extent of its range are unknown.


Myrianida pentadentata is a marine syllid polychaete. Family characteristics include a relatively small and slender body; a prostomium with 2 pairs of eyes, and sometimes eyespots; three antennae and paired palps; an eversible pharynx; the anterior-most segment (peristomium) lacking chaetae, but bearing 1-2 pairs of tentacles; uniramous parapodia (biramous in reproductive individuals); dorsal and ventral cirri on each chaetiger; and a pygidium (anal segment) with 2-3 anal cirri (Pettibone 1963; Blake and Ruff 2007).

During its atokous (non-reproductive) stage, M. pentadentata is slender and uniform in width. The prostomium is wider than long, with four eyes arranged in a trapezoid, and bears three antennae, one located medially. The median antenna extends back to the 9th chaetiger, and is twice as long as the lateral antennae. The palps are small and fused throughout. The anterior-most segment (peristomium) bears two pairs of tentacular cirri. The antennae and the first two pairs of tentacular cirri, and the first pair of dorsal cirri are longer than the cirri on the subsequent segments. The nuchal organs are epaulettes extending from the posterior end of the prostomium to the middle of chaetiger 2. The proboscis is S-shaped and ends in five soft papillae and five teeth. The proventricle is located in chaetigers 12 to 14. The cirri behind the first pair of tentacular cirri are about half the length as the first pair (Imajima 1966b; Nygren 2004).

On the following chaetigers, the cirri alternate between long and short. Each cirrius rises from a ciriophore, and has an annulus (joint) halfway down its length for the shorter cirri, and 2 annuli for the longer cirri. The parapodia are blunt and rounded, but with a pointed neuropodial lobe. The parapodia each bear two bundles of chaetae, much shorter than the cirri. The atokous section, or the last stolon, ends in a pygidium which terminates in a pair of anal cirri. The atokous section is 2.3-6.2 mm long, for worms of 26 to 65 chaetigers, and often with an equal of greater length of stolons. This worm is brightly colored, yellow in the anterior region with red eyes, and brownish-red in the intestinal region (Imajima 1966b; Nygren 2004).

The epitokous stages break off individually from the posterior region of the worm. In three specimens, the epitokes developed behind the 26-51 chaetigers. Unlike M. pachycera, M. pentadentata does not carry a long trail of stolons. The stolons, according to the sex of the worm, develop into morphologically distinct male ('polybostrichus') and female ('sacconereis') forms. These develop new heads with three antennae and one pair of tentacular cirri. The parapodia of the chaetigers bear two bundles of long swimming chaetae. The male form has not been described (Nygren 2004), while one female specimen was 2.6 mm, with 21 chaetigers (Nygren 2004). The female stage, early in development, was packed with green ova (Nygren 2014).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Annelida
Class:   Polychaeta
Subclass:   Palpata
Order:   Aciculata
Suborder:   Phyllodocida
Family:   Syllidae
SubFamily:   Autolytinae
Genus:   Myrianida
Species:   pentadentata


Autolytus pentadentatus (Imajima, 1966)
Myrianida pentadentata (Nygren, 2004)

Potentially Misidentified Species



Myrianida pentadentata, like other members of the Syllidae, reproduces by epitoky. During epitoky the worm undergoes stolonization, in which segments of the body become modified for carrying gametes and swimming (modified setae, enlarged eyes). In M. pentadentata, sexes are separate, and a stolon breaks off from the stem portion of the worm's body and swims in the water column, as an epitoke with a new head, three antennae, and well-developed eyes. Then, the stem portion of the body regenerates a new stolon. Male and female stolons are presumed to be morphologically distinguishable, although the male stolon has not been described (Imajima 1966b; Nygren 2004). The details of fertilization are not known for M. pentatdentata, but in M. pachycera the female carries the fertilized eggs in a long ventral egg mass, while swimming in the water column (Imajima 1966b). Details of development are not known for M. pentadentata, but in the related genus Autolytus, the larvae are brooded and are lecithotrophic (Pettibone 1963).

Myrianida pentadentata is known to occur in warm-temperate climates in Japan and California. It is found in the intertidal and shallow subtidal zones of rocky reefs, marinas, docks, and ships’ hulls (Imajima 1966b; Nygren 2004). Syllids have been considered exclusively carnivorous, including members of the subfamily Autolytinae (inlcuding Myrianida) feeding largely on hydroids (Fauchald and Jumars 1979). However, studies of fecal pellet of syllids indicate that many, including one species of Autolytus) are omnivorous (Giangrande et al. 2000).

Trophic Status:




General HabitatMarinas & DocksNone
General HabitatVessel HullNone
General HabitatRockyNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Maximum Length (mm)6Imajima 1966b; Nygren 2004
Broad Temperature RangeNoneWarm-Temperate
Broad Salinity RangeNonePoly-euhaline

General Impacts

There are no known ecological impacts of Myrianida pentadentata on the West Coast.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3b None 1964 Native Estab
NEP-VI Pt. Conception to Southern Baja California 2001 Def Estab
P050 San Pedro Bay 2001 Def Estab
P020 San Diego Bay 2001 Def Estab
P022 _CDA_P022 (San Diego) 2010 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 2011 Def Estab
NEP-V Northern California to Mid Channel Islands 2014 Def Estab
P030 Mission Bay 2013 Def Estab
P040 Newport Bay 2017 Def Estab
P053 _CDA_P053 (Santa Monica Bay) 2015 Def Estab
P062 _CDA_P062 (Calleguas) 2015 Crypto Estab
P070 Morro Bay 2013 Def Estab
P090 San Francisco Bay 2012 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Blake, James A.; Ruff, R. Eugene (2007) The Light and Smith Manual: Intertidal invertebrates from Central California to Oregon (4th edition), University of California, Berkeley CA. Pp. 309-410

California Department of Fish and Wildlife (2014) Introduced Aquatic Species in California Bays and Harbors, 2011 Survey, California Department of Fish and Wildlife, Sacramento CA. Pp. 1-36

Fauchald, Kristian (1984) Polychaete distribution patterns, or: can Animals with Palaeozoic cousins show larger-scale geographical patterns?, Proceedings of the First International Polychaete Conference <missing volume>: <missing location>

Giangrande, Adriana; Licciano, Margheritia; Pagliaria, Patrizia (2000) The diversity of diets in Syllidae (Annelida: Polychaeta), Cahiers de Biologie Marine 41: 55-65

Imajima, Minoru (1966b) The Syllidae (polychaetous annelids) from Japan II. Autolytinae, Publications of the Seto Marine Biological Laboratory 14(1): 27-83

Nygren, Arne (2004) Revision of Autolytinae (Syllidae: Polychaeta)., Zootaxa 680: 1-314

Nygren, Arne; Pleijel, Fredrik (2010) Redescription of Imajimaea draculai: a rare syllid polychaete associated with the sea pen Funiculina quadrangularis, Journal of the Marine Biological Association of the United Kingdom 90(7): 1441-1448

Pettibone, Marian H. (1963) Marine polychaete worms of the New England region. 1. Aphroditidae through Trochochaetidae., Bulletin of the United States National Museum 227(Part 1.): 1-356

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>

Ruiz, Gregory; Geller, Jonathan (2021) Spatial and temporal analysis of marine invasions: supplemental studies to evaluate detection through quantitative and molecular methodologies, Marine Invasive Species Program, California Department of Fish and Wildlife, Sacramento CA. Pp. 153 ppl.