Fig. 160.—Syllis armillaris Müll. × 2. (From Johnston.) The head is towards the right.
Syllis.—The tentacles and cirri are moniliform; the palps large; there is a single dorsal tooth, which is provided with a poison gland, the duct of which opens near its apex; it is used rather for stabbing its prey than for grasping and tearing. S. krohnii Ehlers, is abundant under stones, and forms tubes of sand; it is nearly an inch long, and consists of some eighty-five to ninety-five segments marked with yellow bands. It may readily be identified by longer dorsal cirri, terminally dilated, alternating with shorter ones. S. cornuta Rathke, has a translucent green body, about half an inch long; no alternation of cirri. Mediterranean, Atlantic, on the Norwegian coast, off Spitzbergen, and on the Madeira coast. S. armillaris Müll. is very common at low water; it is pale yellowish-brown, with a couple of dusky marks on each segment; and measures 2 inches. The dorsal cirri are quite short, consisting of only eight to ten joints. In Pionosyllis the tentacles and cirri are not moniliform; a single dorsal tooth. P. malmgreni M‘I. under stones. Sphaerosyllis.—The dorsal cirri are swollen at the base, and are not moniliform; the long palps are fused along nearly their whole extent. S. hystrix Clap. is only about one-eighth of an inch in length. Exogone Oerst. Grubea Qfg.
Autolytus.—The small palps are entirely fused with the prostomium; the pharynx, which is bent upon itself, is armed with a circle of denticles. Dorsal cirri somewhat foliaceous. There are no ventral cirri. The male and female differ from one another and from the asexual "stock" (see p. [279]). A. pictus Ehl. is abundant under stones. It measures about two-thirds of an inch in length, is darkly coloured with a median lighter band; the anterior dorsal cirri are long. A. prolifer Müll. is common.
Myrianida fasciata Milne Edwards, with its foliaceous cirri, occurs off our coasts (see Fig. 149, p. [280]). Atlantic, Mediterranean.
Fam. 2. Hesionidae.—The body is relatively short, with only a few segments (sixteen to fifty, according to the genus); in the larger forms it is cylindrical. The parapodium is usually uniramous; the dorsal cirri are long and multiarticulate; the chaetae are jointed. The prostomium carries, in addition to four eyes, two or three tentacles, and generally a pair of jointed palps. The peristomium and two or more of the following segments are achaetous, and carry long "peristomial" cirri. The pharynx is very long but unarmed.
Psamathe Johnston, has many segments; head with two tentacles and a pair of three-jointed palps. P. fusca Jnstn. occurs amongst coralline Algae, to which it bears some resemblance, which is heightened by the moniliform cirri. It is a small worm, less than an inch in length. Mediterranean. Castalia punctata Müll. is dirty green or brownish, with a narrow purplish band on each side. It occurs in deeper water than the preceding. In Ophiodromus the head has three tentacles; the palps are two-jointed; there are six pairs of peristomial cirri; the parapodia are biramous. O. vittatus Sars is dredged in numbers off the Scotch coast, and is found also at low tides. It measures 2 inches in length. A closely allied species lives in the ambulacral grooves of the starfish Astropecten.
Fam. 3. Aphroditidae.[[369]]—The most characteristic feature of this family, and one by which its members are absolutely distinguished from all other Chaetopods, is the possession of scales or "elytra" on the back. These flattened dorsal cirri are of a somewhat horny texture, and are carried, generally, on alternate segments of the body; filamentous cirri occurring on the other segments. In the sub-families Hermionina and Polynoina the elytriferous segments are 2, 4, 5, 7, 9, etc., up to 23; then every third segment. The worms are usually short, with some thirty-five to forty-five segments, though Sthenelais and a few others have many more. (For head see p. [262], and for parapodium see pp. [265], [268].) The pharynx is very thick walled, and furnished with two pairs of jaws, which are, however, not hardened in the sub-family Hermionina. The intestine is provided with a number of paired longer or shorter caeca (Fig. 142). A considerable number of this family are commensal or parasitic (see p. [297]). The family is well represented on our own coasts, so that only a few of the more readily distinguishable species can be here described.
Fig. 161.—Polynoë squamata L. Nat. size. c, Notopodial cirrus; e, elytron; f, parapodium; p, palp; t, tentacle. (From Johnston.)
Sub-Fam. 1. Polynoina.—Body flattened, with nearly parallel sides, usually short, more rarely worm-like; three tentacles; peristomium with long dorsal and ventral cirri; the ventral cirri of the next segment are also elongated. Jaws are present. Elytra, usually twelve to eighteen pairs, the surface of which is more or less papillose, and may be "fringed" along the outer border, with long processes. The colouring of the elytra is characteristic in most cases, though liable to considerable variation in some species. The chaetae are generally strong, and of bright golden colour: they are all unjointed. The Polynoina are generally but feeble swimmers, and are mostly found under stones at low tide. Some species have a very wide geographical range.