NIWA Guide to Polychaeta | Shore polychaetes | Shell polychaetes
Shell worm Polydora websteri Spionidae (spionid)
Spionida (Annelida: Polychaeta)
Polydora  websteri  Hartman, 1943.   Family Spionidae  
     Polydora websteri from blister on Crassostrea gigas
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 Identification tips:    Morphology unremarkable. Distinctive colour pattern(s) present; lacking apart from palp groove black pigment (without banding on palps).
 Habitat: Intertidal marine, or inshore marine embayment. Known from mollusc shell. In bivalves. In shell blisters, debri packed. Recorded from living shells of New Zealand commercial shellfish: Crassostrea gigas, Saccostrea commercialis. Occurrences in empty/dead shell also never reported. Tube lining present as packing within mud blister. Tube chimney present as glued debri/sand-grains.
 Nomenclature: Genus Polydora in Family Spionidae. Polydora websteri Described by Hartman, published in 1943, as Polydora websteri. Type locality: USA Atlantic coast, Milford River mouth, Long Island Sound, Connecticut [iczn opinion 1974]. Other synonyms: none recorded
 Description:  Head region: Prostomium tip weakly notched. Occipital antenna absent. Caruncle extends to mid chaetiger 3; separate mid-dorsal organ absent. Colouration: Eyes present, two pairs. Dorsal pigmentation pattern absent. Palp banding black line on groove edge. White mid-body or posterior dorsal pigmentation absent. Branchiae, chaetae, and pygidium: Branchiae adjoining parapodia 7 and following; longest branchiae on chaetiger 9; near body end branchiae present. Anterior gut gizzard-like structure absent. Hooded hooks begin chaetiger 7; bifid, hook shaft constriction (manubrium) present, anterior hooded hook main fang more or less oriented at right angles to the shaft with wide angle to apical tooth. Alternating capillaries adjacent hooded hooks absent; neurochaetal inferior chaetae below hooded hooks absent. Chaetiger one notochaetae absent; notopodial lobe present. Chaetiger 5 elongated relative to adjacent segments. Chaetiger 4 thickened chaetae (similar to those of chaetiger 5) absent. Chaetae of chaetiger 5 'upper' (or 'posterior') row falcate with subterminal lateral flange, 'lower' (or 'anterior') row are hastate tipped 'companion' chaetae. Superior notochaetae of chaetiger 5 present (very flattened, frayed tips). Inferior neurochaetae of chaetiger 5 present. Posterior notochaetal spines absent. Pygidium flattened disc/saucer-rim with dorsal notch/gap. Pygidium large, distinctly wider than last chaetigers.
 Dimensions: Length 24 mm. Width 1.2 mm. Segment total 107. Palps extend to about chaetiger 10.
 Reproduction: Active planktonic dispersal present. Larval nutrition mostly planktotrophic, with early larval release; poecilogony absent or undetected. Reproductive period unknown.
 Distribution:  World distribution includes New Zealand and elsewhere. Known to be anthropochoric/invasive. Global distribution includes New Zealand mainland, Australia, within south east coast and Tasmanian zone, North America, Pacific coast (to Panamanian Isthmus). P. websteri appears to be common in the warmer north of New Zealand where feral Crassostrea gigas has large intertidal populations. It may be rare further south although Handley found small numbers in the Marlborough sounds area in Pecten novaezelandiae, and in subtidally-cultured C. gigas..
 Remarks:  Polydora websteri is an alien shell-blistering species present in New Zealand probably since the 1960s, possibly related to the accidental introduction or invasion of Crassostrea gigas which occurred around the same time. However, there are no verified voucher specimens prior to the early 1990s.
 Biology: Polydora websteri is 'well-known' with an extensive literature on its occurrence in commercial shellfish worldwide, but some of this may be tainted by inclusion of, or confusion with, similar species. Feeding group: Surface deposit/filter-feeding.
 Best References:   Biology: Read (2004) (In press) Polydora websteri and P. haswelli (Polychaeta: Spionidae) confirmed as mudblister worm species in New Zealand shellfish.. New Zealand Journal of Marine and Freshwater Research 38: Taxonomy: Radashevsky (1999) Description of the proposed lectotype for Polydora websteri Hartman in Loosanoff & Engle, 1943. Ophelia 51:107-113.

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The information provided by this page and by the pages of the "more information" links is held in a structured form for rapid and frequent updating and improvement. Descriptive text is compiled from a number of database fields, some of which may occasionally be empty.
Data last edited 20/07/2004  (dd/mm/yy), and page last generated by G. Read, 25/07/2004  (dd/mm/yy)