Chapter XVII: Introduction: Nematoda—anatomy—embryology—classification—ascaridae (7)

FAM. 1. _Syllidae._—These are small worms, the majority being less than an inch long, so that they are not easily observed. {307}The body consists of a fair number of segments.[368] In many genera a dorsal bundle of unjointed, natatory chaetae makes its appearance at maturity. The palps, which are grooved, are in some cases so united with one another and with the prostomium as to be scarcely recognisable. (For head see p. 262, and for feet see p. 264.) The pharynx is armed with one or more teeth. There is a special gizzard, following the pharynx, and provided with thick, muscular walls of peculiar structure. Following the gizzard, the oesophagus receives in many genera a pair of T-shaped diverticula, that are used for storing water, which is swallowed with food. These diverticula are absent in _Autolytus_ and other free-swimming forms. The reproduction of the members of this family is interesting, and has already been described (p. 278).

_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 {308}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 {309}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.

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, {310}and are mostly found under stones at low tide. Some species have a very wide geographical range.

_Polynoë._[370]—The body is short; none or only a few segments at the end of the body are uncovered by the elytra, except in the long body of _P. johnstoni_.

_A. With twelve pairs of elytra._—In _P. squamata_ Linn. the elytra entirely cover the body and conceal the head, each elytron overlapping the next posterior one, and those of the two sides overlapping. General colour sandy-brown, speckled, lighter or darker. The fringed elytra are very firmly fixed to the body. The notopodial chaetae scarcely project from below the elytra. The worm is common between tide-marks and in the coralline region, is about one to one and a half inches in length, and about one-third of an inch in width. Atlantic. _P. clava_ Montagu, may attain a larger size, though it is generally smaller. The elytra are dark, usually grey, mottled with white or light grey, unfringed, and do not overlap to so great an extent as in _P. squamata_, so that the middle of the back and the hinder part of the body is more or less exposed. This is never the case in the preceding species, but even here it is subject to variation in extent, depending on the amount of food contained by the worm or on the ripeness of the genital products. It occurs in the Mediterranean.[371]

_B. With fifteen pairs of elytra._—_P. imbricata_ L. is probably the commonest species of the genus, occurring nearly everywhere under stones at low tide. It is about an inch in length; the elytra are deciduous, and are very variously coloured and marked; sometimes uniformly grey or even black, sometimes {311}mottled with brown: in other specimens each elytron has its outer half pale or white, while its inner half is darker, usually some tint of brown or olive green, so that the worm appears to have a dark band along the middle of its back. Other patterns occur. The body is entirely covered by the elytra. The chaetae project considerably, and are nearly as long as half the width of the body; those of the notopodium are brown and are directed upwards, being nearly as long as the golden neuropodial chaetae. This species has a very wide range, occurring on both sides of the Atlantic, even on the shores of Nova Zembla, and reappearing again at Japan. _P. semisculptus_ Leach is rather larger than the foregoing. The elytra are very readily detached: they are light in colour, without a fringe, but with large papillae near the margin. The notopodial chaetae are thicker than those of the neuropodium. Several other species are also common, but _P. johnstoni_ v. Marenz.[372] differs from the rest in having an elongated body of some seventy segments, so that the posterior half is uncovered by the elytra, which are small, greenish-grey, speckled, and have no fringe. It is common and widely distributed, but appears to be only found in the tubes of _Terebella nebulosa_.

_C. With eighteen pairs of elytra._—_P. gelatinosa_ Sars, may attain a length of 2 inches. The elytra are very faintly coloured, transparent and soft, attached by rather long peduncles. In spirit they become swollen and folded, giving the worm a very untidy appearance. The prostomium is partly overlapped by a peculiar collar-like fold of the peristomium.

_D. With numerous pairs of elytra._—_Lepidasthenia_ has a very long body, consisting of more than eighty segments. The elytra are quite small, and occur throughout the body on the usual segments. There are no notopodial chaetae. _L. elegans_ Gr. is a very elegantly marked worm, which, however, has not been recorded from the British area; it occurs in the Mediterranean (see Fig. 156, p. 293).

Sub-Fam. 2. _Hermionina._—The body is short, oval and {312}depressed; the particularly strong notopodial chaetae are directed upwards and backwards so as to protect the elytra. The neuropodial chaetae are also strong. The prostomium carries a single tentacle and two long palps; the prostomial ridge may be well developed. The peristomium is chaetigerous, with long cirri. The jaws are represented merely by thickened prominences.

_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 {313}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 {314}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 {315}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 {316}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 {317}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_ {318}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, {319}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 {320}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 {321}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 {322}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 {323}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 {324}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.

{325}_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.

{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.

_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]

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]:—

{328}

{ equal in _Amphitrite_.
{ 3 pairs, { size. 24 notopodia.
A. Capillary chaetae { which are {
confined to the { { unequal in _Terebella_.
anterior part of Gills { { size. 17 notopodia.
body; commencing ramose. {
on the fourth { { Gills equal.
segment. { { Eye-spots. _Nicolea._
{ 2 pairs. {
{ 17 notopodia. { Gills unequal
{ and of _Pista._
{ peculiar shape.

B. Capillary chaetae { arborescent; 3 pairs. _Leprea._
throughout the {
body; commencing Gills { filiform; in transverse
on the third { series in two _Thelepus._
segment. { segments.

_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 {329}seventeen gland shields are red, and continuous from segment to segment. The gill is shown in Fig. 176, C. North Sea, Atlantic, and Mediterranean.

_Nicolea venustula_ Mont. has only two pairs of equal, arborescent gills (Fig. 176, D); the tentacles are comparatively few. The animal, which is about an inch in length, is cinnamon-yellow with white spots, and has seventeen gland shields. 20 fathoms, North Sea and Mediterranean. _Pista cristata_ Müll. is readily recognised by the shape of the gills (Fig. 176, E), of which there are only two pairs. Each consists of a long peduncle, bearing a number of dichotomously dividing, rather spirally-arranged branches, the whole having the appearance of a "bottle-brush." The worm is 2 to 4 inches long, of greyish-red to yellow colour. Atlantic east and west (even at the mouth of the Congo), and Mediterranean. _Thelepus cincinnatus_ Fabr. is about the same length, pale red in colour, marked on its back with clear areas, giving the appearance of lacework. The gills are represented by numerous unbranched filaments arising separately in two transverse rows. The tube, which is adherent to shells, etc., along its whole length, is of thin, transparent, and flexible material like mica, covered with foreign bodies, and even with Polyzoa and Hydrozoa. 30 fathoms, Atlantic and Mediterranean.

{330}_Polycirrus aurantiacus_ Gr. is sometimes placed in a special sub-family, as it has no gills. The numerous tentacles are very long, and arise from a great hood over the mouth; the capillary chaetae commence in the first segment and extend for about half the length of the body; the uncini commence in the ninth segment. The ventral "shields" are paired. The animal is highly coloured; its phosphorescence and its distastefulness have already been mentioned on p. 294. In _Terebellides stroemi_ Sars, four comb-like gills arise from a single common thick peduncle on the back of the second segment (Fig. 176, F). The ventral surface of the body bends upwards anteriorly so as to bring the mouth to the dorsal surface. 13 to 16 fathoms, muddy bottoms, North Sea and Mediterranean.

FAM. 3. _Ampharetidae._—This family differs from the Terebellids chiefly in the shape of the head and in the presence of a bundle of strong chaetae (or paleae) on each side of the head in front of the gills, of which there are four on each side. Each gill is a simple filiform process, considerably longer than the tentacles, which are very few in number. _Amphicteis gunneri_ Sars, _Ampharete gracilis_ Mgrn., and _Melinna cristata_ Sars, occur on our coasts.

FAM. 4. _Amphictenidae._—This contains the interesting genus _Pectinaria_, in which the head is protected by great golden chaetae on the second segment; they are flattened, curved, and pointed, and are arranged in a single transverse row on each side, serving as an operculum to the tube. The posterior end of the worm has undergone great degeneration, and is represented by a small leaf-like "scapha" which serves to close the tube posteriorly. The worm is 1½ inches in length and consists of only twenty segments, of which seventeen are chaetigerous. The tube is nearly cylindrical, but wider anteriorly than posteriorly (Fig. 152, p. 288); the sand grains are uniform in size, and are embedded in the secreted mucus in a very regular way, the surface being smooth both {331}inside and out. These tubes can be carried about by the worm, but may be found projecting from the sand at very low tides. _P. belgica_ Pall. forms a straight tube, whilst in _P. auricoma_ Müll. the tube is larger and slightly curved. The former species appears to be confined to the North Sea; the latter occurs in deeper water, and is also present in the Mediterranean.

SUB-ORDER 4. CAPITELLIFORMIA.

FAM. _Capitellidae._[389]—_Capitella capitata_ v. Ben. occurs pretty frequently in the sand under stones near low tide-mark. It is a red worm, about 1½ to 2 inches long, greatly resembling a Tubificid Oligochaete. It may readily be distinguished from other Polychaeta by the strong genital chaetae in the male, which replace the notopodial chaetae of segments 8 and 9; those in the former segment are pointed backwards, and in the latter forwards. There is but a single pair of generative ducts in either sex in the eighth segment. North Sea, Mediterranean.

_Notomastus latericeus_ Sars is a longer worm, living in shallow water, off our coast and in the Mediterranean. The anterior twelve segments are wider than the rest of the body. The notopodial chaetae of the anterior segments of the hind body form a ring. _Dasybranchus caducus_ Gr., which occurs in the Mediterranean, but not on our coast, reaches a length of 2 or 3 feet. It has gills on the hinder segments above the neuropodia.

_Mastobranchus_ Eis. is found in the Mediterranean.

SUB-ORDER 5. SCOLECIFORMIA.

FAM. 1. _Opheliidae._—Comparatively short, rather ugly worms of a pearly colour, no prostomial processes: parapodia obscure. The family is represented in British waters by four species, occurring in shallow water.

_Ammotrypane aulogaster_ Rathke, is about 2 inches long; the nearly cylindrical body has a ridge running along each side below the chaetae. The conical prostomium is tipped with a small knob, and carries at each side a ciliated pit (Fig. 144, p. 273). Every segment, except the first chaetigerous, is provided with a filamentous gill (dorsal cirrus). The segmentation {332}is very obscurely marked, for internally there are only three complete septa, placed far forwards. The intestine is bent upon itself. In _Ophelia limacina_ Rthk. the gills commence in the eighth segment, and the longitudinal ridge does not extend in front of this segment. The worm is about 1½ inches long, and occurs between tide-marks. _Travisia forbesi_ Jnstn., North Sea. _Polyophthalmus pictus_[390] Duj. is very abundant at some parts of the coast. There are two bundles of chaetae on each side of every segment; each bundle contains three chaetae, of which only one projects to any distance. Paired eye-like spots exist on the sides of twelve segments. The worm is about an inch in length.

FAM. 2. _Maldanidae_ (= _Clymenidae_).—Represented on our coasts by four fairly common species. They form sandy tubes, which are embedded in the sand with a short portion projecting. In some places they are so abundant that at low water the sand has quite a rough appearance. The prostomium is frequently truncated and depressed, and is always fused with the peristomium. A horny plate may be developed on the upper surface of the head, and the skin at the side of the prostomium is frequently raised into a more or less prominent fold. The hinder end of the body carries a funnel surrounding the anus. There are no gills or sensory processes on the body. Some of the segments towards the middle of the body may be longer than the rest. Peculiar serrated hooks of characteristic shape constitute the neuropodial "torus." The buccal region is eversible.

_Nicomache lumbricalis_ Fabr. is a rosy-pink worm with white spots anteriorly; the chaetigerous ridges are red. The worm consists of twenty-six segments, and measures 2 or 3 inches. It is very narrow and readily breaks in pieces. The prostomium is laterally compressed; the anal funnel is fringed with a number of short equal processes. Under stones in the Laminarian zone.

_Axiothea catenata_ Mgrn., which may reach a length of 3 or 4 inches, resembles the above in general colour, though of a deeper tint. There are only eighteen chaetigerous segments. The head has a membranous fold of skin on each side, and the anal funnel is produced into longer and shorter processes. Both {333}these species are also found on the west side of the Atlantic. _Clymene lumbricoides_ Qfg. is about 8 inches long; pink, with a light ring round each segment; the seventh segment is larger and reddish-brown. The prostomium is laterally compressed. Anus on a cone, which rises from the bottom of a funnel, the margin of which is entire. Atlantic.

FAM. 3. _Arenicolidae._—Here belongs the common "lug-worm" _Arenicola marina_ L., which occurs all round our coasts between tide-marks, and is so generally used as bait in fishing. The worm, which measures 5 to 8 inches, is of a dark tint, usually brownish-green. It burrows to a depth of some 18 inches or 2 feet, and throws up a considerable quantity of "castings" or "sand-ropes," which are noticeable on every shore consisting of mud or muddy sand. The body of the worm is cylindrical, thicker anteriorly; the segments are indistinct, owing to the secondary groovings and furrows on the skin. The prostomium is in the adult fused with the peristomium; this and the second segment are achaetous. Then follow twenty chaetigerous segments with dorsal bundles of capillary chaetae and ventral rows of short crotchets. The hinder region of the body is achaetous and narrower than the rest, forming a "tail." There are twelve (sometimes thirteen) pairs of arborescent red gills on segments 9 to 20 (21). Internally there are {334}only four complete septa, and six pairs of nephridia, which are of large size: the fore-gut is eversible. Atlantic and Mediterranean. A second and smaller species, _A. ecaudata_ Jnstn., occurs on our southern coasts; it is readily distinguished by the absence of a "tail," the chaetae and gills being continued to the end of the body.

FAM. 4. _Scalibregmidae._—Prostomium ill-marked, fringed with small processes. Parapodia represented by slight papillae; two bundles of chaetae; usually cirriform lobes above and below them. _Lipobranchius jeffreysii_ M‘I. has a grub-like body pointed at each end; forms tubes of mud. Firth of Clyde and elsewhere in North Sea. _Sclerocheilus_ Gr. in old oyster shells. Channel, Mediterranean. _Eumenia crassa_ Oerst. has gills on first six segments. North Sea. _Scalibregma inflata_ Rthke. has arborescent gills on segments 4 to 7. The anterior part of the body is dilated. North Sea.

FAM. 5. _Chlorhaemidae._—The family derives its name from the green colour of the blood, due to chlorocruorin. The representatives are comparatively short worms, with capillary chaetae on all the segments, the limits of which are not evident. The prostomium carries a pair of long grooved yellowish processes, which are perhaps palps, and several green tentacles, acting as "gills," arranged in a transverse series above the mouth (Fig. 134, F, p. 262). The peristomium is achaetous; the whole "head" can be withdrawn into the body. The chaetae of the anterior segments are especially long, and directed forwards so as to form a "cage" for the head. The body-wall is covered with longer or shorter papillae. Internally, the chief points of interest are the presence of only two septa (_Trophonia_) or only one septum (_Siphonostoma_), situated somewhere in front of the middle of the body, and forming a great backwardly-directed pouch, which contains a part of the looped intestine, and the nephridia, of which there are only two or four.

_Trophonia plumosa_ Müll. is about 2 to 4 inches long, yellowish-brown in colour, with a rough skin; the head is usually retracted. It lives in the mud amongst Laminarian roots down to 50 fathoms. North Atlantic. _Siphonostoma_ (_Flabelligera_) _diplochaitos_ Otto, has a transparent body-wall, so that the coloured viscera are visible. The skin carries long papillae, which traverse a thick jelly-like envelope secreted by it, in {335}which numerous diatoms live (symbiotically?); the surface is covered by particles of mud, etc. This species, which may be found under stones at low tide, occurs also in the Mediterranean.