Fig. 174.—Cirratulus tentaculatus Mont. (½ nat. size). (From Règne Animal.)

Chaetozone setosa Mgrn. occurs in the North Atlantic. Dodecaceria concharum Oerst. is about an inch in length, olive-green or brownish in colour, and is not uncommon amongst roots of Laminaria. It is stated to live also in tortuous tubes bored in shells and stones, but whether it makes these tubes is uncertain. The worm has two thick tentacular filaments, and the thinner gills are only on four segments. Hekaterobranchus shrubsolii Buch.[[386]] is a small worm some ½ inch long, found at Sheerness, where it occurs at low tide in soft mud; here it forms a loosely coherent tube, though it also moves freely in the mud. Its chief features are (1) a pair of long, ciliated "cephalic tentacles," probably peristomial, and similar to the "tentacular filaments" of Dodecaceria; (2) a pair of filamentous gills (dorsal cirri) on the first chaetigerous segment; (3) a pair of large green nephridia in the anterior segments. The describer placed it amongst the Spionids, but the above and other features point to Cirratulid affinities.

Fam. 2. Terebellidae.—The body is cylindrical, and generally larger in front than behind. The prostomium is generally flattened, and forms a mobile upper lip, which always carries a transverse series of many tentacles; it may bear "eye-spots," but never palps; the lower lip is formed by the peristomium. There are one to three pairs of gills, which are usually more or less branched, on as many segments.[[387]]

The chaetigerous lobes are small; the dorsal ones contain capillary chaetae, which are frequently confined to the anterior segments, whilst the ventral chaetae are uncini. The ventral surface of the anterior segments is thickened by glands which secrete the mucus employed in tube-building; the number of these "shields" and of the dorsal bundles of chaetae have to be noted in identifying the worms. There are one to three pairs of large anterior nephridia. A very strong "diaphragm"—usually more or less pouched—cuts off this anterior region of the body-cavity from the rest, and is the only complete septum in the body; from three to twelve pairs of small generative ducts occur behind it. The family is tubicolous, foreign materials being generally used in the formation of the tube.

Fig. 175.—Amphitrite johnstoni (½ nat. size). g, Gills; t, prostomial tentacles. (From Cunningham and Ramage.)

There are six genera which are fairly common round our coast, and their identification may be facilitated by means of the following table[[388]]:—

A. Capillary chaetae confined to the anterior part of body; commencing on the fourth segment.

Gills

ramose.

 3 pairs, which are equal in size.

Amphitrite.

24 notopodia.
unequal in size.

Terebella.

17 notopodia.

2 pairs.

17 notopodia.

Gills equal.

Eye-spots.

 Nicolea.
Gills unequal and of peculiar shape. Pista.
B. Capillary chaetae throughout the body; commencing on the third segment. Gills arborescent; 3 pairs. Leprea.
filiform; in transverse series in two segments. Thelepus.
A. Capillary chaetae confined to the anterior part of body; commencing on the fourth segment. Gills
ramose.		 3 pairs, which are equal in size. Amphitrite.
24 notopodia.
unequal in size. Terebella.
17 notopodia.
2 pairs.
17 notopodia.		 Gills equal.
Eye-spots.		 Nicolea.
Gills unequal and of peculiar shape. Pista.
B. Capillary chaetae throughout the body; commencing on the third segment. Gills arborescent; 3 pairs. Leprea.
filiform; in transverse series in two segments. Thelepus.

Amphitrite johnstoni Mgrn. (Fig. 175) is brown in colour, about 4 to 6 inches in length, and nearly ½ inch in breadth anteriorly. Each of the gills consists of a curved stem; from the convex side of which arise a number of branches, themselves dichotomously divided, the final branches being long (Fig. 176, A). There are twelve ventral "gland shields." The worm is fairly common between tide-marks, below stones in muddy places: the end of its tube of mud projects above the surface. Atlantic.