Invasion HistoryFirst 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 (http://australianmuseum.net.au/image/Myrianida-pachycera/), 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 (http://www.flickriver.com/photos/top_down/9429696118/), 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 (http://www.nikonsmallworld.com/galleries/entry/2003-photomicrography-competition/2)
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).
Fishes, crabs, shrimps
Other free-moving polychaetes
|General Habitat||Coarse Woody Debris||None|
|General Habitat||Oyster Reef||None|
|General Habitat||Marinas & Docks||None|
|General Habitat||Vessel Hull||None|
|General Habitat||Unstructured Bottom||None|
|General Habitat||Coral reef||None|
|Salinity Range||Polyhaline||18-30 PSU|
|Salinity Range||Euhaline||30-40 PSU|
|Tidal Range||Low Intertidal||None|
Tolerances and Life History Parameters
|Minimum Length (mm)||2.4||Male reproductive epitoke, preserved (Nygren 2004). Female epitokes are 5-6 mm|
|Maximum Length (mm)||120||A mature worm with a long train of stolons (Imajima 1966b; Nygren 2004).|
|Broad Temperature Range||None||Warm temperate-Tropical|
|Broad Salinity Range||None||Polyhaline-Euhaline|
Economic and ecological impacts are unknown for Myrianida pachycera.
Regional Distribution Map
|Bioregion||Region Name||Year||Invasion Status||Population Status|
|P050||San Pedro Bay||2000||Def||Estab|
|P060||Santa Monica Bay||2000||Def||Estab|
|P020||San Diego Bay||2000||Def||Estab|
|CAR-I||Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida||1997||Def||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|
|NEP-V||Northern California to Mid Channel Islands||2015||Def||Estab|
|P090||San Francisco Bay||2015||Def||Unk|
|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|
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