Audouin & Milne-Edwards, 1830
Body of this scale-worm long, tapering posteriorly. Dorsal surface smooth, with ctenidia on the base of the elytrophores, dorsal tubercles, and posterior surface of parapodia. Ventral surface smooth.
Prostomium round with a small median antenna posterior to the eyes (this is easily overlooked or dislodged), a pair of short lateral antennae, a pair of palps and two pairs of eyes close together in a central position. First segment with numerous capillary chaetae and a pair of dorsal and ventral tentacular cirri. Scales cover the body. They occur on segments 1, 3, 4 and 6, then alternately to the 26th then on all segments. Scales are round to rectangular, on the posterior margin 4-16 papillae with about 18 lateral branches, a short papilla on the posterior margin and smooth surfaces. On the first chaetiger a pair of round discs occur on the dorsal surface. Three ctenidia, attached to the dorsal surface of notopodia appear on all segments except the 1st and 2nd segments which have one. Cirri occur above the ctenidia on all chaetigers from the 3rd chaetiger. A pair of small dorsal cirri present on the 2nd chaetiger. Notopodia bulbous with numerous chaetae and a terminal finger-like projection. Notopodial chaetae spinose capillaries with bifid tips. Neuropodia with projecting acicular lobe, an anterodorsal tubercle and numerous chaetae (S. mathildae-detail). Neuropodial chaetae of 4 kinds: 1) simple with whorls of spines; 2) compound with multiarticulate blades with up to 14 articles, bidentate tips and spinose shafts; 3) compound, with multiarticulate blades with 2-6 articles, bidentate tips and smooth shafts; 4) compound, stout blade with one article, bidentate tips and smooth shafts.
Up to 150 mm for 200 chaetigers.
Littoral to 36 m, in sand.
North Pacific, North Atlantic up to Mediterranean, Adriatic, English Channel, North Sea up to Kattegat. Also found in Persian Gulf and Madagascar.