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Goniadidae
Description
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The prostomium is conical and annulated, and bears four
small terminal appendages. A
long, muscular eversible pharynx is present; it bears one pair
of large jaws and a dorsal and ventral arc of numerous smaller
denticles, which together form a complete circle. Pharyngeal
papillae are well developed and are of several types; they may be differentiated along the pharynx.
Terminal pharyngeal papillae are present. The peristomium is
reduced to lips. The first segment has parapodia and is similar
to subsequent segments. Parapodia are anteriorly uniramous
with neuropodia and dorsal cirri only, and posteriorly
biramous with notopodia almost as large as neuropodia. Dorsal and ventral cirri are present
throughout. Coelomic loops (see Glyceridae) and branchiae
are absent. Aciculae are present. Notochaetae, where present,
are spines (straight or distally curved); neurochaetae are
compound spinigers and falcigers. One pair of
pygidial cirri is present.
This description is taken from Wilson (2000), which in turn is based on that of Fauchald & Rouse (1997).
Identification tips
Recognising the family
Goniadids are strong, muscular polychaetes with long bodies almost circular in cross-section. Live specimens exhibit a characteristic thrusting movement and the body wall is often irridescent. The conical prostomium tapering to a fine tip with 4 small terminal appendages is distinctive and goniadids are only likely to be confused with the closely related Glyceridae. The two families are readily distinguished if the eversible pharynx is examined: goniadids have a single pair of large jaws and numerous smaller jaw articles arranged in a circle, while glycerids possess 4 similar-sized jaws arranged in a cross. Parapodial morphology is also useful: goniadids always lack
notopodial lobes on anterior chaetigers, but have well developed notopodial lobes on posterior chaetigers while in glycerids notopodial lobes are present throughout the body (in all glycerid genera except Hemipodus which lacks notopodial lobes entirely).
Distinguishing species
Many of the most important characters for recognising taxa within the Goniadidae are located on the eversible proboscis: the number of jaw articles, the presence or absence of paired lateral V-shaped processes called chevrons and the structure of the pharyngeal papillae. The number and shape of parapodial lobes and the number of prostomial and segmental annulations are also useful characters.
Complete animals are required for accurate identification and it helps if the pharynx is extruded to reveal the structure of the chevrons and pharyngeal papillae. In bulk-preserved benthic samples this is rarely the case, but if live specimens can be dealt with, low concentrations of alcohol will encourage the pharynx to be everted before placing in formalin for preservation.
Description | Identification
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