Aphrodite.—The fifteen pairs of elytra, arranged as in Polynoë, are concealed by a "felting" of hair-like chitinous threads arising from the notopodium (Fig. 139, p. 268). A. aculeata L.—The "sea-mouse" is one of the most beautiful of the Polychaetes. The small tentacle is very readily detached; the palps are very long; the parapodia of the peristomium are directed forwards so as to form lateral lips; and its cirri are not especially modified (see Fig. 132, p. 260). The body, which measures 3 to 6 inches, consists of thirty-five to forty segments, and is broadest in the middle, the last dozen segments being very small; the body terminates in a point. Some of the notopodial chaetae are brilliantly iridescent, and give the worm its characteristic coloration. It is fairly common in the coralline regions, and is frequently thrown ashore after storms. Atlantic and Mediterranean.

In Hermione the "felt" is absent, so that the elytra are exposed. H. hystrix Sav. occurs in ten to thirty fathoms of water all over the British area and Mediterranean. It resembles in its general appearance a fat Polynoid, with strong chaetae. Laetmonice filicornis Kinb. also occurs on our north-west coasts, and L. producta Gr. has been dredged in 500 fathoms off the west coast of Ireland; it has been recorded also from Kerguelen and from Japan, so that it has a very wide distribution.^[373]

Sub-Fam. 3. Acoetina.^[374]—The long, vermiform body has some thirty-nine to ninety-three pairs of elytra, placed on every alternate segment throughout. It is represented in the British area by Panthalis from 75 fms., which forms a tube of black mud.

Sub-Fam. 4. Sigalionina.—This sub-family includes forms with a long, vermiform body; anteriorly the elytra are on alternate segments, up to the twenty-sixth, and posteriorly on every succeeding segment; "gills" here coexist with elytra; cirri are absent. The prostomium in Sthenelais Kinb. has a median tentacle, which is absent in Sigalion Aud. and Edw. Sth. boa Jnstn. is common off our coasts near low-water mark, where it burrows in the loose sand with rapidity. It is an elegant worm, and may attain a length of 8 inches, though it is generally smaller; it is narrow, flat, and only slightly tapering at each end; the elytra, which may be more than a hundred pairs, are greyish or slightly brownish, some being lighter than others; the margin is fringed with simple processes (which in Sigalion are pinnate). Atlantic and Mediterranean. In Psammolyce the elytra are covered with sand grains. British and Mediterranean.

Fam. 4. Phyllodocidae.—The members of this family make use of the foliaceous cirri (Fig. 136, F) in their very active movements. The rounded prostomium bears four or five tentacles; there are four long peristomial cirri on each side (see Fig. 134, E).

Sub-Fam. 1. Phyllodocina.—The body is elongated, with numerous segments; the eyes are small; the chaetae are jointed; the dorsal and ventral cirri are foliaceous; the pharynx is covered with papillae externally, but contains no "jaws."

Phyllodoce has a more or less depressed body; four prostomial tentacles; four pairs of peristomial cirri. P. lamelligera Jnstn.^[375] (the "paddle-worm") may reach a length of 24 inches, but is usually 8 to 12 inches long and ½ inch across. The general colour is bright bluish-green or yellowish-green, with metallic iridescence; the parapodia olive-green or brown, the sensory processes yellow. It lurks, during day, under stones and shells, etc., in the Laminarian zone. The green egg masses, so frequently referred to as belonging to Arenicola, are laid by Phyllodocids.^[376]

In Eulalia an additional (fifth) tentacle arises from the middle of the back of the prostomium. E. viridis Müll. is a dark green worm smaller than the preceding; common between tide-marks, hiding in cavities and tunnels in limestone rocks, which have been bored by the mollusc Saxicava; it is rare where such rocks are absent. It might have been thought that its vivid colour would harmonise with its surroundings, but it is most abundant in regions where Fucus abounds and Ulva is absent. It is evident then that the colour is not protective; it may perhaps be of warning significance, for the mucus secreted in quantities by glands on the cirri of the Phyllodocids is probably objectionable to their enemies. Phalacrophorus Grf. and Pontodora Grf. may be mentioned as pelagic genera.

Sub-Fam. 2. Lopadorhynchina.—This includes small forms, Lopadorhynchus Gr., Pelagobia Grf., and other pelagic genera.

Sub-Fam. 3. Alciopina.—These are surface forms, and, like most pelagic animals, are colourless and transparent; the eyes, however, are very large, and, with certain brown spots in each segment,^[377] are the only coloured parts in the body; in structure the eyes are much more complicated than those of other Polychaetes. The prostomium has five tentacles; there are long peristomial cirri, and in general their anatomy agrees most closely with that of Phyllodocids. Alciope, Asterope, Vanadis, Nauphanta are genera of the family;^[378] none have been recorded from the British area.

Fam. 5. Tomopteridae.^[379]—This includes but one genus, Tomopteris, which is pelagic. The transparent, colourless body consists of only a few (eighteen to twenty) segments; the parapodia are as long as the body is wide, and carry no chaetae; each is bilobed, and fringed with a membrane; each of these lobes contains a yellow rosette-shaped photogenic organ. The only chaetae present in the worm are on the "head." The prostomium is hammer-shaped, and appears to carry a pair of short filaments ventrally (Fig. 167, x) each with a single chaeta within it; and a longer filament laterally (y), supported by a long, very delicate chaeta. The mouth is behind these, and they probably are the first pair of parapodia which have shifted forwards. T. onisciformis Eschscholtz is not unfrequently obtained off our shores in the tow-net.

Fam. 6. Nereidae (Lycoridae).—This family contains a very large number of species, differing from one another in small and not readily recognisable characters, such as the relative lengths of the various processes of the head, of the lobes of the feet, the arrangement of the "paragnaths" (see Fig. 125, d) and so forth. The general features of the family have been already described. The genus Nereis is represented by six fairly common species on our coast, which are almost world-wide in distribution.

N. diversicolor Müll. is about 3 to 4 inches in length, of a general fleshy-red colour, though tending in some cases to yellowish-brown or even greenish. It may be distinguished by two diverging brown bands, which start on the peristomium and pass backward one along each side of the body for several segments. The prostomium is broader than it is long. The worm burrows in mud or sand, all round our coast between tide-marks. It has a very wide distribution, being met with on this side of the Atlantic, and off the coast of Greenland, and off Japan. It is even found in brackish water at Bembridge, Isle of Wight.

N. cultrifera Gr. is green or greenish-grey, with a series of small rectangular light spots along the mid-dorsal surface, and oblique light lines at the sides of each segment. Posteriorly the greenish pigment becomes less and less till the hinder segments are flesh-coloured. The prostomium is as long as it is broad. This species attains a length of 6 inches. Southern coasts: locally known as "Red Cat."

N. dumerilii Aud. and Edw. is rather smaller and narrower than the two preceding species; it is reddish-violet in colour, marked with darker transverse lines in each segment. It is readily recognised by the two dark brown spots on the upper surface of the base of the notopodium in most of the segments, and by the great length of the peristomial cirri, the longest of which reaches the fifteenth segment. It is sometimes found enclosed in a cocoon-like tube of hardened grey mucus, more or less covered with foreign particles, such as sand grains. Atlantic, Mediterranean, Japan.

N. pelagica L. is red-brown or bronze in colour, and is generally larger than the other species, from which it is distinguished by being widest about the middle of the body (see Fig. 122, p. 246); whilst in the preceding species the greatest breadth occurs at the segments immediately following the head. Further, the palps are long, the peristomium is twice as long as the next segment, and the back of the worm is strongly arched. At all depths on rocky and stony ground. Northern coasts.

N. (Nereilepas) fucata Sav. lives in the topmost whorls of empty whelk shells and in those occupied by hermit crabs. The ground colour is tile-red, with two milk-white bands along the dorsal surface. The dorsal lobe of the foot is slightly foliaceous, glandular, and vascular.

N. (Alitta) virens Sars. is a giant amongst Polychaetes, reaching a length of 18 inches. Its name suggests its colour; it is very plentiful at certain times at St. Andrews, and between tide-marks along the shore of the Mersey estuary, as well as elsewhere. It forms a burrow in the clay, etc., of the shore, and lines it with mucus, which is abundantly secreted by the great foliaceous lobes of the parapodia. These great leaf-like lobes of the foot recall the modification which the foot of many species of Nereis undergoes in transformation into Heteronereis: they are so greatly developed that, at first sight, the worm might be mistaken for a large Phyllodoce. The worm is known as the "Creeper," and is much esteemed as bait on some parts of our coast.

Fam. 7. Nephthydidae.—The elongated body is quadrangular in section, the dorsal and ventral surfaces being almost flat. (For head see p. 262, and for parapodium, p. 264.) The two lobes of the parapodium are widely separated, and each is fringed with a membrane, while a sickle-shaped "gill" hangs down from the under surface of the notopodium. The pharynx is enormous. Of the genus Nephthys two species, called the "Lurg" or "White Cat" by fishermen, occur on our coasts. Their active movements and beautiful mother-of-pearl tint are characteristic. N. hombergii Aud. and Edw. occurs on the shore, and down to 20 fathoms; it is 3 or 4 inches long, and may be found burrowing in the sand; the chaetae exceed in length those of N. caeca Fabricius, which occurs less frequently and in deeper water, and is larger than the preceding. Both are Atlantic forms.

Fam. 8. Amphinomidae.—The body in this family is either vermiform, as in Eurythoe, or oval and flattened, as in Euphrosyne and Spinther. The head carries a peculiar sense organ, the "caruncle," consisting of a smooth axis with the sides folded so as to look like a number of lamellae. The parapodia carry gills. Most of the Amphinomids are tropical and Southern forms.

Eurythoe borealis Oerst. measuring 6 inches, occurs all round the British area, from the Shetlands, where it occurs in deep water, to the Channel Isles, where it lives on shore, under stones, etc. (For parapodium of Amphinome see p. 264.)

Euphrosyne.—The body is short, oval, and flattened. The parapodia are not distinct processes, but the chaetae extend from each side of each segment nearly to the middle dorsal line, and are absent ventrally (Fig. 137, C, p. 265). The dorsal and ventral cirri are more or less filiform, and there is an intermediate similar process on the back (? = lip of chaetigerous sac). Amongst the chaetae are a number of curious branched processes—usually called "gills."^[380] The presence of these and of the chaetae give the upper surface of the body a fluffy appearance. E. foliosa Aud. and Edw. is fairly common under stones on our southern shores. It is about an inch in length and is of a cinnamon-red colour.

Fam. 9. Eunicidae.—The elongated body is provided with parapodial gills in more or fewer segments (except in Lumbriconereis). The "gills" may be cirriform (Hyalinoecia), pectinate (Eunice, Onuphis), or more complex (Diopatra). The notopodium is represented by a lobe (usually called "cirrus") into which an aciculum projects; in some cases it even contains a few chaetae; most of the neuropodial chaetae are jointed (Fig. 138, F). The prostomial tentacles vary in number; they may be three or five, or five and two short "frontal palps," or they may be absent. Peristomial cirri are absent, though in Eunice, Diopatra, and Onuphis "nuchal cirri" are present on the dorsal surface of the second segment (Fig. 134, D). One of the most characteristic features in the anatomy of the Eunicids is the peculiar jaw apparatus (see p. 270). The majority of the genera form permanent tubes of parchment-like consistency, which may be further strengthened by the addition of grains of sand, small pebbles, etc.; the tubes may be branched.

Eunice has five tentacles, two great palps, and a pair of nuchal cirri; the gills are pectinate, and there are four anal cirri. E. harassii Aud. and Edw. is about 8 inches long. It is reddish-brown, with white spots down the back, one to each segment, and others at the sides. The gills begin at the sixth segment, and when fully developed have eleven branches. The dorsal cirrus is not longer than the gill. E. philocorallia Buch.^[381] forms its tube amongst the branches of Lophohelia prolifera, in 200 fathoms, off the west coast of Ireland.

Marphysa resembles Eunice, but has no nuchal cirri. M. sanguinea Mont. is a fine bronze colour, with bright red gills, which commence on the twentieth segment, and have only four or five branches. The worm, which measures 12 to 18 inches, and is as thick as one's finger, hides in clefts in rocks and under stones below low water. Mediterranean. It is known as "Rockworm" in the Channel Islands.

Hyalinoecia Mgrn., in addition to the five prostomial tentacles and palps, possesses a pair of small "frontal palps" arising from the anterior border of the prostomium; there are no nuchal cirri, and the gills are simple filiform processes. H. tubicola Müll., about 3 inches long, is yellowish-brown, and forms a transparent, parchment-like tube. Atlantic and Mediterranean.

Onuphis Oerst. has a head like the preceding, from which it differs in having pectinated gills and two nuchal cirri like Eunice. In making its tube it employs small pebbles, bits of shell, and even echinid spines, which it glues together with mucus, so that it bears a general resemblance to its surroundings. O. conchylega Sars, has a flattened, scabbard-like tube, which can be carried about by its owner. Atlantic.

Lumbriconereis has a more or less conical prostomium, without any tentacles, but with large palps: segments without gills. L. fragilis Müll. is reddish or brownish, with a beautiful iridescence; it is cylindrical, very narrow, and some 5 or 6 inches long; L. tricolor Jnstn. is much larger.

Ophryotrocha (Fig. 170) is a small form often occurring in aquaria; it is chiefly remarkable for the possession of segmentally-arranged girdles of cilia—a permanent larval feature. Lysidice ninetta Aud. and Edw. belongs here.

Fam. 10. Glyceridae.—Elongated worms with numerous segments. The prostomium, though narrow, is long, conical, annulated, and carries at its apex four very small tentacles; at its base a pair of palps. Special retractile gills are present. The armed pharynx is very long, and when protruded appears wider than the animal. The members of this family are without any system of blood-vessels, but the coelomic corpuscles are coloured red. Glycera has four jaws, the parapodia are all alike (Fig. 136, C). G. capitata Oerst. is 2 or 3 inches in length, is yellowish in colour, with a dark-red median line. It may be found burrowing in sand. The setigerous lobes of each foot are coalesced to form one large lobe with pointed apex. The dorsal cirrus is a small wart above the base of the foot. Atlantic and Mediterranean. A second species, which is much larger and flesh-coloured, also occurs.

Goniada is distinguished from the preceding by the fact that the parapodia suddenly change in size and character at about one-third the length of the body. The pharynx has numerous paragnaths. G. maculata Oerst. occurs off our coasts.

Fam. 11. Sphaerodoridae.—The dorsal and ventral cirri of each segment are spherical. The chaetae are usually jointed, and there is an aciculum to each parapodium. Ephesia Rthke. (E. gracilis R. = Sphaerodorum peripatus Jnstn.) is exceptional in having unjointed chaetae. North Sea, Arctic Ocean, and the Channel. The family, which is much modified, is allied in some respects to the Syllidae.

Fam. 12. Ariciidae.—These worms burrow in sand between tide-marks. The body consists of many short segments, and is nearly cylindrical. The prostomium is more or less pointed; the chaetae are all capillary; in the first few segments they project laterally but soon come to lie dorsally, and are carried by slight conical papillae (supported by acicula), which are longer in the middle of the body. Most of the segments carry filiform "gills," representing the dorsal cirri (Fig. 137, B).

Scoloplos armiger Müll. is extremely common on our coast. It is about an inch long, yellowish, with red gills, commencing about the twelfth segment. Each of the lobes of the parapodium possesses an aciculum, and the chaetae are bent in a peculiar way. The everted buccal region has the form of a six- or eight-rayed star. The spawn of this species may be found on the shore in spring as brown, pear-shaped, jelly-like masses, each with a long stalk, by which the mass is fixed to the sand. In the jelly are the eggs, which may be watched passing through the earlier stages of development. Atlantic on both shores, even off Spitzbergen, and Nova Zembla. Another representative is Theodisca mamillata Clap., which occurs amongst the roots of Laminaria.

Fam. 13. Typhloscolecidae.^[382]—Pelagic, greatly modified forms, apparently related to the Phyllodocidae, but with very uncertain affinities. The prostomium is pointed and carries a pair of foliaceous tentacles; each of the first two segments bears a pair of foliaceous cirri; the remaining segments possess a dorsal and a ventral pair of foliaceous cirri, with a small bunch of chaetae and a single aciculum. All the cirri have peculiar rod-cells. Typhloscolex Busch, Sagitella Wagner, and Travisiopsis Uljanin: all small worms. North Sea Atlantic.

Sub-Order 2. Spioniformia.

Fam. 1. Spionidae.—Mostly small worms, with small ridge-like prostomium carrying a pair of eyes, but no tentacles or palps. The peristomium, which extends forwards on each side of the prostomium, bears a pair of very long cirri (usually termed "tentacles") normally directed backwards, very mobile, and more or less coiled. They are readily thrown off by the animal. The notopodial cirri are long, finger-shaped, and curved over the back; they are vascular and ciliated, and function as "gills." The neuropodia project laterally. Both are usually provided with a "podal membrane" along their outer margin. There are no ventral cirri; the dorsal chaetae are fringed capillaries; the ventral are "crotchets." The buccal region is eversible. The worms burrow in mud and sand.

Spio seticornis Fabr. is a small worm less than an inch in length, colourless except for the red blood in its vessels. It builds long and flexible tubes of sand in the clefts of rocks and under stones in the upper part of the littoral zone. The prostomium is notched at the anterior margin. The gills commence on the twelfth segment, and do not extend to the end of the body. A membrane-like cirrus exists also on the second chaetigerous segment. The podal membrane is adnate to the gill throughout its extent. Four short anal cirri occur. Greenland and Scandinavia.

Nerine is represented by two species, sometimes called "Ragworms." The genus is very similar to Spio, but the worms are of larger size. The prostomium is compressed by the forward growth of the peristomium, and appears as a ridge on the latter segment, extending downwards in front towards the mouth. The "gills" commence on the second segment, and are continued in every segment except the hindmost. Nerine (Scolecolepis) vulgaris Jnstn. is readily distinguished from other species by its somewhat T-shaped prostomium. It is an extremely common worm under stones and amongst seaweed at low water. It is some 3 or 4 inches in length and more slender than the following species. Its colour is yellowish-brown, and the red gills directed upwards and backwards give the appearance of oblique red lines. The podal membrane does not reach the tip of the gill. North Atlantic. It is said to ascend rivers and live in brackish water. N. coniocephala Jnstn. is much the same colour, but reaches a length of 8 inches, and a diameter of ¼ inch. The prostomium is conical. The podal membrane reaches to the tip of the gill in the anterior segments. The worm burrows rather more deeply and nearer low-water mark than the preceding species.

Fam. 2. Polydoridae.—Polydora Bosc (= Leucodore Jnstn.) is readily distinguished from the other Spionids, and, indeed, from any other Polychaet (except Chaetopterus), by possessing specially strong chaetae in the enlarged fifth chaetigerous segment. The anterior segments differ from the rest in the absence of gills and in the character of the chaetae (Fig. 133, A, p. 261).

P. ciliata Jnstn. inhabits soft mud tubes near low water; it also makes U-shaped galleries in stones and shells, and the tube projects from each mouth. The worm is about ½ inch long, consists of some forty segments, and is yellowish or flesh-coloured. The prostomium resembles that of Spio; the peristomium is raised into a slight collar at each side. The anus is surrounded by an incomplete funnel. The species has almost a world-wide distribution, having been recorded from Iceland, Australia, the Philippine Islands, as well as from the European seas. P. coeca Oerst. often lives commensally with a sponge, having a protective odour.

Fam. 3. Chaetopteridae.—The family is represented on our coasts by Chaetopterus variopedatus Ren.,^[383] which is found at the Channel Islands, the Scilly Isles, the Isle of Man, and the west Scottish coast, and probably at various other places, at low water and down to a depth of some 15 fathoms. It occurs in all European seas. The animal builds a long tube, the basis of which is a tough, parchment-like substance; this is coated externally with sand, small pebbles, and other débris: it is of considerable length and about ¾ inch in diameter, is U-shaped and open at both ends, the greater part of it being embedded in sand or in crevices of rocks. The animal, whose body-wall is thin and delicate, never leaves its tube. The body has a bizarre appearance; three regions are readily distinguishable, which may be denoted by the letters A, B, and C. The most anterior region, A, is flattened, and carries nine pairs of conical lobes with delicate chaetae, though the fourth lobe possesses special stouter chaetae (as in Polydora). The anterior end of the body terminates in a wide funnel, the boundary of which is formed chiefly by the peristomium; on its dorsal surface is a pair of tentacle-like processes (peristomial cirri); the region between which represents the prostomium.

The second region, B, is very curiously modified; it is formed of five segments. The most anterior is produced on either side into a great wing-like process, which in life is directed forwards above the region A. Each is grooved on its inner side, the ciliated grooves being continuous with a median groove running forwards along the back of A; this apparatus serves to bring food to the great funnel-like mouth. The next segment (twelfth) carries a dorsal and ventral "sucker," representing the parapodia. Each of the segments 13, 14, 15 carries a membranous fold encircling the body. By the constant movement of these "fans," which have nearly the same diameter as the tube, a current of water is constantly washed over the animal. The fans represent the notopodia; the neuropodia are bilobed rounded knobs. The region C consists in the adult of about thirty segments, all alike, and less modified than the preceding. The animal is the most truly tubicolous of the Polychaetes, and is much modified on this account. No locomotor chaetae are present, though the great wings and notopodial processes of region C contains chitinous bristles, which, however, do not project;^[384] the anterior region with its stiff chaetae, and the neuropodial uncinal plates of the rest of the body serve in its movements up and down the tube, while the "suckers" fix the worm temporarily to the wall of its house.

Chaetopterus is highly phosphorescent (see p. 295). It is further interesting on account of the green colouring-matter, which is extracted by alcohol. Two commensal Polynoids occur in the tube, viz. Polynoë glabra and P. cirrosa. The larva is "mesotrochal" (with a ciliated ring round its middle), that region of the body lying in front of the cilia giving rise to the region A, whilst the rest of the body gives rise to regions B and C.

Fam. 4. Magelonidae.—This family includes only the very peculiar worm, Magelona papillicornis Fr. Müll., which lives buried in sand, between tide-marks, in various parts of our coast and that of the United States. Its chief features are the large, flat, spoon-shaped prostomium; the long peristomial cirri, slightly expanded terminally, carrying papillae along one side; the enormous, eversible buccal region, which is an important respiratory organ. The blood is of a madder-pink colour, and the blood-vessels in the thorax are greatly dilated. The body of the worm is divisible into two well-marked regions, owing to differences in the chaetae.^[385]

Fam. 5. Ammocharidae.—This family contains only one species, Owenia filiformis D. Ch. Some of the anterior segments are longer than the hinder ones, though the arrangement of chaetae is alike throughout. The mouth is wide, like that of Chaetopterus, and is surrounded, except ventrally, by a membrane, so deeply notched as to give rise to flattened filaments containing blood-vessels. These "gills" appear to belong to the peristomium. The small worm in its sandy tube is plentiful on our coasts in about 20 fathoms. Off Greenland and the Mediterranean.

Sub-Order 3. Terebelliformia.

Fam. 1. Cirratulidae.—These worms have a cylindrical body, more or less attenuated at each end; the segments are distinct, and similar throughout, with capillary chaetae on each side in two bundles, carried by small papillae. The prostomium is conical, the peristomium usually without cirri. On more or fewer segments the dorsal cirri are long and filamentous, and function as gills. There is a single pair of anterior nephridia: the septa and genital ducts are repeated throughout the hinder part of the body. The worms usually live in burrows.

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.

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.

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

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.

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.