Terebella (Polymnia) nebulosa Mont. is distinguished by its bright red colour, spotted with white; it is 6 or 7 inches in length, and ½ inch across. Large specimens of this beautiful worm may be obtained at Weymouth and elsewhere on the south coast, where it lives in about 14 fathoms. Each gill appears much more arborescent than in the preceding (Fig. 176, B); it consists of a main stem, from which comparatively few branches arise; these subdivide frequently, and the terminal branchlets are quite short. The "gland shields" are fourteen to sixteen in number. The tube is of mud. North Sea and Mediterranean. T. (Leprea) lapidaria L. is 1 inch in length, orange-red in colour; and has 12 ventral shields. The tube, of fine mud, lies horizontally on the under surface of stones.
T. (Lanice) conchilega Pall. (the "sand mason") forms a very characteristic tube of sandy particles, small pebbles, and pieces of shell. It is buried in the sand, but a short portion protrudes, and bears, set round its edge, a fringe of branching sandy threads (Fig. 153) commonly seen on sandy shores between tide-marks. The worm may be distinguished from the preceding species by the fact that the series of fourteen to seventeen gland shields are red, and continuous from segment to segment. The gill is shown in Fig. 176, C. North Sea, Atlantic, and Mediterranean.
Fig. 176.—Gills of various Terebellids. × 4. A, Amphitrite johnstoni Mgrn.; B, Terebella nebulosa Mont.; C, T. conchilega Pall.; D, Nicolea Mgrn. (the finer branches are not indicated); E, Pista Mgrn.; F, Terebellides Sars (after Malmgren). g, Gill; m, mouth; t, tentacles.
Nicolea venustula Mont. has only two pairs of equal, arborescent gills (Fig. 176, D); the tentacles are comparatively few. The animal, which is about an inch in length, is cinnamon-yellow with white spots, and has seventeen gland shields. 20 fathoms, North Sea and Mediterranean. Pista cristata Müll. is readily recognised by the shape of the gills (Fig. 176, E), of which there are only two pairs. Each consists of a long peduncle, bearing a number of dichotomously dividing, rather spirally-arranged branches, the whole having the appearance of a "bottle-brush." The worm is 2 to 4 inches long, of greyish-red to yellow colour. Atlantic east and west (even at the mouth of the Congo), and Mediterranean. Thelepus cincinnatus Fabr. is about the same length, pale red in colour, marked on its back with clear areas, giving the appearance of lacework. The gills are represented by numerous unbranched filaments arising separately in two transverse rows. The tube, which is adherent to shells, etc., along its whole length, is of thin, transparent, and flexible material like mica, covered with foreign bodies, and even with Polyzoa and Hydrozoa. 30 fathoms, Atlantic and Mediterranean.
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.
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 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.