Dasychone bombyx Dalyl. is a short, comparatively stout worm usually 1 to 1½ inches long; reddish-brown in colour, with a darker spot on each side of every segment. The gills are lighter with greenish marks. This worm may readily be recognised, for each of the gill filaments carries some six to ten pairs of dark compound eyes at intervals along its length, and near to each pair there arise two short processes from the outer side of the filament, which are known as "dorsal appendices." The worm forms a tube of mud, more or less mixed with sand. It occurs at low water and to some depth round the coasts of the Atlantic, North Sea, and Mediterranean.
Chone infundibuliformis Kröyer may be recognised by the absence of lobes on the collar, the presence of a membrane connecting the gill filaments, and the passage of the faecal groove along the dorsal surface of the thorax. The worm is 6 inches long, with purple gills, spotted with yellowish-white. The tube is formed of yellowish membrane covered with sand, and is fixed to stones and other objects. Potamilla reniformis Müll. is about 3 inches long, with about twelve brown gill filaments, some of which have eyes near the base. The tube is transparent and horny, with sometimes a slight covering of sand. Found in old oyster shells. North Sea, Atlantic, Mediterranean.
The genus Spirographis contains one of the largest European Sabellids, S. spallanzanii Viv., which occurs off the Channel Islands and in the Mediterranean. The two gill plumes are unequal; the large rone forms an upright, spirally-coiled column.
Fam. 2. Eriographidae.—Myxicola infundibulum Mont. has its gill filaments connected by a membrane reaching nearly to their tips. Each gill plume forms a semicircle; there are no eyes; the peristomium does not form a collar; no gland shields. The worm requires neither of these structures, since it is practically a free-swimmer, envelopes itself in mucus, and moves tail first. The faecal groove is not well marked, though continued dorsally. In the abdomen the tori uncinigeri extend dorsally and ventrally (beyond the neuropodial chaetae) and nearly encircle the body. The animal is 4 or 5 inches long, dull green, with purplish gills. Between tide-marks. North Sea and Mediterranean.
Amphiglena mediterranea Leyd. is only about ¼ inch long, hermaphrodite, and has eyes on the peristomium and on the anal segment. It is a very elegant little worm, and as a living object under the microscope, with the cilia on the gills, is very beautiful. The gills consist of six filaments on each side, provided with the usual double row of ciliated processes.
Fam. 3. Amphicorinidae.—Small hermaphrodite Sabellids in which each gill tuft contains only a few branching filaments. The simplest form is Haplobranchus aestuarinus Bourne,[[394]] which occurs in the rather foul mud at low tide in the estuaries of the Thames, the Liffey, and other rivers. The animal is about ¼ inch long, with four finger-shaped processes on each side, and a pair of larger, vascular processes on the ventral surface. These five branches are gills (palps), although, owing to the small size of the worm and simple vascular system, the four lateral filaments have no blood-vessels. The animal consists of only eleven chaetigerous segments, and lives in a tube made of mud particles.[[395]] Fabricia sabella Ehrenb. (Amphicora fabricia Müll.) has three gills on each side, each with a number of secondary branches of different sizes, but so arranged as all to reach the same level. It has eyes in its tail and swims backwards.
Fam. 4. Serpulidae.—The thorax is provided with an undulated membrane on each side, chiefly employed in smoothing the inside of the tube; it represents the dorsal and ventral cirri of these segments. The gland shields are confined to the thoracic segments. In many genera the dorsalmost gill filament on one or both sides is terminally dilated and serves as an operculum. The tube is calcareous, and attached to rocks, shells, etc., for a greater or smaller part of its extent.
Serpula vermicularis L. forms a pinkish tapering tube about 3 inches long; the narrower fixed end is coiled. It is marked at irregular intervals with encircling ridges, indicating cessation in formation, and has a circular aperture. The worm itself is about 1½ inches long. The horny operculum is conical, with its base upwards, fringed with short processes. 20 fathoms in the North Sea and Mediterranean; also from 275 fathoms off the west coast of Ireland.
Pomatoceros triqueter L.—The white shell is adherent, with a distinct keel along its upper surface; the aperture is overhung by a spine. The tubes are abundant everywhere, attached to rocks, stones, shells, etc., between tide-marks and down to 18 fathoms. The animal is very handsome, the thorax being deep blue, the abdomen red in the female, whitish in the ripe male. The branchiae are barred and spotted with blue, orange, and white; the operculum is calcareous, and furnished with a couple of horn-like processes.
