Invasion History

First Non-native North American Tidal Record: 1990
First Non-native West Coast Tidal Record: 1990
First Non-native East/Gulf Coast Tidal Record: 1997

General Invasion History:

Myrianida pachycera was described from Shark Bay, Australia. It is known form New South Wales (, the Seychelles (Böggemann et al. 2003), China (Huang 2001), and from the southern coast of Japan (Imajima et al. 1996b). Occurrences of this polychaete in Hawaii, California, and Florida probably represent introductions by shipping (Cohen et al. 2002; Nygren 2004; Imajima 1996b). This worm is frequently photographed, because of its bright colors and unusual appearance.

North American Invasion History:

Invasion History on the West Coast:

Myrianida pachycera was first seen in southern California sometime between 1986 and 2000 (Leslie Harris, personal communication, Cohen et al. 2000). In 2000-2001, it was found in San Diego Bay, Los-Angeles-Long Beach Harbor, Marina del Rey, King Harbor, and Port Huemene (Cohen et al. 2002; Nygren 2004; Cohen et al. 2005). Nygren (2004) collected it in epifauna on a ship. Transport in ship fouling is likely, as is ballast water transport of the reproductive stages.

Invasion History on the East Coast:

Myrianida pachycera was collected in the Indian River Lagoon, southern Florida, in 1997, in intertidal oyster beds (Nygren 2004). A specimen was photographed in the lagoon in 2013 by Dean Janiak (, so this worm is presumed to be established in the Lagoon. Again, ship fouling or ballast water are likely vectors.

Invasion History in Hawaii:

Myrianida pachycera was first collected in Hawaii in Kaneohe Bay, Oahu in 1959. It has also been found in Pearl Harbor, where it was first collected in 1976-1977. It was associated with coral rubble, sponges, seaweeds, and fouling communities (Carlton and Eldredge 2009).

Invasion History Elsewhere in the World:

In 2016, three specimens of M. pachycera were found on fouling plates at Puerto Ayora, on Santa Cruz Island in the Galapagos Islands (Keppel et al. 2019).


Myrianida pachycera 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). Reproduction in M. pachycera involves growing multiple segmented body sections (stolons), each of which can break off and swim away, then breaking apart to release eggs or sperm. The atokous (non-reproductive) section of the body consists of the prostomium, peristomium (anterior-most segment, lacking chaetae), and about 30–33 chaetigers, which are followed by a train of up to 10 stolons (Imajima 1966b; Nygren 2004).

Myrianida pachycera, in the atokous (non-reproductive) stage, is slender, and tapered posteriorly, with the ventral surface flattened and the dorsal surface arched. The prostomium has four eyes, arranged in a trapezoid, and bears three antennae, one located medially. The median antenna extends back to the 8th chaetiger. The lateral antennae are about half as long as the median antenna. The palps are small, directed ventrally, and fused at the base. 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 grooves extending from the posterior end of the prostomium to chaetigers 4 to 7. The proboscis is S-shaped and ends in 9 soft papillae. It contains a ring (trepan) of 11–16 large teeth and 26–28 smaller teeth. The proventricle extends to chaetigers segment 8–10 or to 11–13. The cirri behind the first pair are shorter, broad, and blade-like, about as long as the body-width. 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 40–60 mm long, and often with an equal or greater length of stolons. This worm is brilliantly colored, with red eyes, bright-blue cirri, light blue parapodia, and a bright-orange central region. Except for a few anterior setigers, most have a bright blue dot in the center of each segment (Imajima 1966b; Nygren 2004).

The epitokous stages break off from the chain of stolons and 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. A preserved male specimen was 2.4 mm long, with 22 chaetigers (Nygren 2004), while females were 5–6 mm, with 31–35 setigers (Imajima 1996b; Nygren 2004). The female stages, early in development, are packed with ova, and later carry an external egg mass on their ventral surface (Imajima 1996b; Nygren 2014).

It is a favorite subject for photography because of its bright colors and long chains of stolons. One picture of this worm, by Dr. Greg Rouse, won 2nd place in a 2003 Nikon photomicrography contest (



Taxonomic Tree

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


Autolytus pachycerus (Augener, 1913)
Autolytus purpureimaculata (Okada, 1933)
Myrianida crassicirrata (Hartman-Schroeder, 1965)
Myrianida pachycera (Imajima, 1966)

Potentially Misidentified Species



Myrianida pachycera, 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). Sexes are separate, and the stolons break off from the stem portion of the worm's body, and swim in the water column as epitokes, with new heads, three antennae, and well-developed eyes. The stolons then regenerate. Male and female stolons are morphologically distinguishable (Imajima 1966b; Nygren 2004). The details of fertilization are not known, but 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 but in the related genus?Autolytus, the larvae are brooded and are lecithotrophic (Pettibone 1963). 
Myrianida pachycera occurs in warm-temperate to tropical climates, in the intertidal and shallow subtidal zone. It can be found in a variety of habitats including rocky reefs, oyster beds, coral reefs, muddy-silty bottoms, marinas, docks and ships’ hulls (Imajima 1966b; Nygren 2004; Carlton and Eldredge 2009). Syllids have been considered exclusively carnivorous, including members of the subfamily Autolytinae (including?Myrianida) feeding largely on hydroids (Fauchald and Jumars 1979). However, studies of fecal pellet of syllids indicate that many are omnivorous, including one species of Autolytus (Giangrande et al. 2000). 


Algae, invertebrates


Fishes, crabs, shrimps


Other free-moving polychaetes

Trophic Status:



General HabitatCoarse Woody DebrisNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatVessel HullNone
General HabitatUnstructured BottomNone
General HabitatCoral reefNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Life History

Tolerances and Life History Parameters

Minimum Length (mm)2.4Male reproductive epitoke, preserved (Nygren 2004). Female epitokes are 5-6 mm
Maximum Length (mm)120A mature worm with a long train of stolons (Imajima 1966b; Nygren 2004).
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Economic and ecological impacts are unknown for Myrianida pachycera

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-3a None 0 Native Estab
AUS-X None 0 Native Estab
P050 San Pedro Bay 2000 Def Estab
S190 Indian River 1997 Def Estab
P062 _CDA_P062 (Calleguas) 2000 Def Estab
P060 Santa Monica Bay 2000 Def Estab
SP-XXI None 1959 Def Estab
P020 San Diego Bay 2000 Def Estab
EA-V None 0 Native Estab
AUS-IV None 0 Native Estab
AUS-III None 0 Native Estab
NWP-2 None 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1997 Def Estab
NWP-3b None 1933 Native Estab
NEP-VI Pt. Conception to Southern Baja California 1990 Def Estab
P050 San Pedro Bay 2000 Def Estab
P090 San Francisco Bay 2015 Def Estab
P050 San Pedro Bay 2001 Def Estab
P053 _CDA_P053 (Santa Monica Bay) 2000 Def Estab
NWP-4a None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2015 Def Estab
GAden Gulf of Aden 0 Native Estab
SEP-Z None 2016 Def Estab
P030 Mission Bay 2013 Def Estab
P040 Newport Bay 2017 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
26988 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-30 Pilots Dock at Pier F Def 33.7472 -118.2156
27328 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-29 Marina del Rey Def 33.9722 -118.4522
27821 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-25 Anacapa Isle Marina Def 34.1731 -119.2269
28595 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-26 Chula Vista Boat Ramp Def 32.6211 -117.1031
29186 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-29 King Harbor Def 33.8464 -118.3969
32867 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-26 Shelter Island, Mission Bay Def 32.7100 -117.2342
32971 Cohen, et al. 2002 (So Cal Exotics RAS) 2000 2000-08-31 Long Beach Yacht Club Def 33.7536 -118.2808
767538 Ruiz et al., 2015 2013 2013-07-30 Hilton Resort Docks, Mission Bay, CA, California, USA Def 32.7791 -117.2128


Atlas of Living Australia 2013-2016 Atlas of Living Australia. <missing URL>

Australian Museum 2014 Atlas of Living Australia- Data Sets. <missing URL>

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

Boggemann, Markus; Hessling, Rene; Westheide, Wilfried (2003) Horizontal distribution of the syllid fauna (Annelida: Polychaeta) in the fringing reef lagoon of Anse Forbans (Mahe, Seychellles) and redescription of the abundant Streptosyllis aequiseta, Hydrobiologia 496: 17-26

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

Carlton, James T.; Eldredge, Lucius (2009) Marine bioinvasions of Hawaii: The introduced and cryptogenic marine and estuarine animals and plants of the Hawaiian archipelago., Bishop Museum Bulletin in Cultural and Environmental Studies 4: 1-202

Cohen, A. N. and 11 authors (2005) Rapid assessment survey for exotic organisms in southern California bays and harbors, and abundance in port and non-port areas., Biological Invasions 7: 995-1002

Cohen, Andrew N. and 10 authors (2005) <missing title>, San Francisco Estuary Institute, Oakland CA. Pp. <missing location>

Cohen, Andrew N. and 12 authors (2002) Project report for the Southern California exotics expedition 2000: a rapid assessment survey of exotic species in sheltered coastal waters., In: (Eds.) . , Sacramento CA. Pp. 1-23

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

Huang, Zongguo (Ed.), Junda Lin (Translator) (2001) Marine Species and Their Distributions in China's Seas, Krieger, Malabar, FL. Pp. <missing location>

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

Keppel, Erica; , Keith, Inti; Ruiz, Gregory M.; Carlton, James T. (2019) New records of native and non-indigenous polychaetes (Annelida: Polychaeta) in the Galapagos Islands, Aquatic Invasions 14(1): 59-84

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

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

Quintanilla, Elena; Thomas Wilke; Ramırez-Portilla, Catalina; Sarmiento, Adriana; Sanchez, Juan A.2017 (2017) Taking a detour: invasion of an octocoral into the Tropical Eastern Pacific, Biological Invasions <missing volume>(17): 2583–2597
DOI 10.1007/s10530-017-1469-2

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.

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.