{326}_Cirratulus._—The prostomium is long, sometimes annulated. In addition to the segmental filamentous "gills" there is a transverse row of long "tentacular filaments" across one of the anterior segments, and it has been suggested that they are really prostomial tentacles which have shifted backwards. They and the gills twist about in a very active fashion during life, and look like small independent worms, especially when they are detached. _C. cirratus_ Müll, is a brown or dirty yellowish worm about 4 to 6 inches in length, usually to be found under stones, partially embedded in the mud or sand. The prostomium carries a pair of linear groups of "eye-spots"; the first chaetigerous segment carries a transverse row of tentacular filaments, and the red gill-filaments commence on the same segment. Common. _C. tentaculatus_ Mont. is a larger worm, dark red in colour, and is distinguished from the preceding by the absence of eyes and by the fact that the tentacular filaments are on the seventh chaetigerous segment, while the gills commence more anteriorly. Atlantic and the Mediterranean. [Illustration: 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 {327}"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]