{330}_Polycirrus aurantiacus_ Gr. is sometimes placed in a special sub-family, as it has no gills. The numerous tentacles are very long, and arise from a great hood over the mouth; the capillary chaetae commence in the first segment and extend for about half the length of the body; the uncini commence in the ninth segment. The ventral "shields" are paired. The animal is highly coloured; its phosphorescence and its distastefulness have already been mentioned on p. 294. In _Terebellides stroemi_ Sars, four comb-like gills arise from a single common thick peduncle on the back of the second segment (Fig. 176, F). The ventral surface of the body bends upwards anteriorly so as to bring the mouth to the dorsal surface. 13 to 16 fathoms, muddy bottoms, North Sea and Mediterranean. FAM. 3. _Ampharetidae._—This family differs from the Terebellids chiefly in the shape of the head and in the presence of a bundle of strong chaetae (or paleae) on each side of the head in front of the gills, of which there are four on each side. Each gill is a simple filiform process, considerably longer than the tentacles, which are very few in number. _Amphicteis gunneri_ Sars, _Ampharete gracilis_ Mgrn., and _Melinna cristata_ Sars, occur on our coasts. [Illustration: FIG. 177.—_Pectinaria belgica_ Pall. Slightly enlarged. _a_, Neuropodial chaetae; _b_, notopodium; _ch_, paleae; _g_, gills; _sc_, scapha; _t_, prostomial tentacles; _I_, peristomium. (From Malmgren.)] FAM. 4. _Amphictenidae._—This contains the interesting genus _Pectinaria_, in which the head is protected by great golden chaetae on the second segment; they are flattened, curved, and pointed, and are arranged in a single transverse row on each side, serving as an operculum to the tube. The posterior end of the worm has undergone great degeneration, and is represented by a small leaf-like "scapha" which serves to close the tube posteriorly. The worm is 1½ inches in length and consists of only twenty segments, of which seventeen are chaetigerous. The tube is nearly cylindrical, but wider anteriorly than posteriorly (Fig. 152, p. 288); the sand grains are uniform in size, and are embedded in the secreted mucus in a very regular way, the surface being smooth both {331}inside and out. These tubes can be carried about by the worm, but may be found projecting from the sand at very low tides. _P. belgica_ Pall. forms a straight tube, whilst in _P. auricoma_ Müll. the tube is larger and slightly curved. The former species appears to be confined to the North Sea; the latter occurs in deeper water, and is also present in the Mediterranean. SUB-ORDER 4. CAPITELLIFORMIA.