Quick guides - scale worms

Six polychaete families have two dorsal rows of scales. The interactive key to polychaete families distinguishes these exhaustively (select character "dorsal cirri: modified as elytrae"), but the following table may also help:

Acoetidae	Only Acoetidae and Aphroditidae have silky fibre-like chaetae. Only Acoetidae construct a membranous tube. Only Acoetidae and Polynoidae have an incised prostomium.
Aphroditidae	Distinctive "furry" chaetae, often sediment encrusted; aptly known as sea-mice. Unique in lacking lateral prostomial antennae; only a single medial antenna is present. Rows of golden modified dorsal chaetae, "palae", may be present (only in this family)
Eulepethidae	Neuroaciculae uniquely elongated, axehead-shaped distally. First chaetiger with neurochaetae only or with both notochaetae and neurochaetae (all other families either without chaetae or with notochaetae only)
Pholoidae	Unique in not being dorsoventrally flattened, and in having elytrae with concentric growth rings. Only Pholoidae and Sigalionidae have compound chaetae and lack spines.
Polynoidae	A scale worm with only 14 or fewer body segments must be a polynoid (though beware: the converse is not true). But, if the distinctive characteristics of other scale worm families are not present then the specimen probably belongs in the Polynoidae (a warning that this family is probably not a monophyletic group).
Sigalionidae	Only Pholoidae and Sigalionidae have compound chaetae and lack spines. Sigalionidae have smooth, unjointed prostomial antennae whereas in Pholoidae the antennae are divided into a basal ceratophore and distal ceratostyle.