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Nereididae: Perinereis vallata (pharynx partially everted)

The prostomium is triangular to T-shaped and is at its widest posteriorly. It has one pair of antennae, rarely a single antenna or none, and one pair of articulated ventral palps. The peristomium and the first segment are fused and carry two to four pairs of tentacular cirri, four pairs in most genera. The tentacular cirri are derived from peristomial cirri and tentacular cirri from the first segment, but the peristomium and first segment are fused; the distinction is only apparent during development. The muscular eversible pharynx is differentiated into distinct regions; it has a pair of lateral jaws and usually accessory denticles (paragnaths) or papillae (or both) are present in a regular arrangement. Terminal papillae are absent. Nuchal organs are present as short ciliated grooves, barely exposed. Notopodia and neuropodia are present, usually each with at least one flattened lobe. Aciculae are present. Notochaetae may be compound spinigers or falcigers or both; neurochaetae include compound spinigers and falcigers in two fascicles. All chaetae are compound, but chaetal articulation may be fused in posterior segments in some taxa. One pair of pygidial cirri is present.

The above description is taken from Wilson (2000), which in turn is based on the studies of Glasby (1993) and Fauchald & Rouse (1997).

Identification tips

Recognising the family
Nereidids are the only polychaete family which combines the following characters: eversible pharynx with one pair of lateral jaws; first segment with tentacular cirri; prostomium bluntly conical to trapezoidal.

Distinguishing species
Species and genera are distinguished by the presence or absence of paragnaths, the type of paragnaths present and their precise distribution on the pharynx. (If not everted then the pharynx must be dissected with a ventral incision. Placing live material briefly into 95% ethanol will encourage the eversion of the pharynx before being placed in formalin for fixation.) The pharynx is divided into a standard grid, within which sections are denoted by Roman numerals I to VIII; certain sections are more useful than others, in particular I and V. Other characters used are the distribution and type of chaetae in both notopodia and neuropodia along the body. Colour patterns are useful in live and freshly preserved material. Adult animals without the epitokal modifications associated with reproduction are necessary for identification.


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