P. rhododactyla. A transparent spherical body, one inch to one and a half inches in diameter, with eight combs or plates of flat cilia extending from pole to pole. At one pole is the mouth, like a slit, at the other a small area in the center of which is an eye-spot. From the body hang two tentacles, half a yard or more in length, fringed with cilia. The tentacles are very contractile and can be rolled up or expanded with great rapidity; they take graceful curves as the animal moves rapidly through the water. Pleurobrachia has a pink tint, and prismatic colors play over it from the vibrating cilia. It is a beautiful and interesting creature to watch. Found along the shores of Massachusetts and Maine.
Genus Bolina
B. alata. Slightly oval in form; lower part of the body divided into two large lobes which hang below the mouth. Four of the swimming-plates are shorter than the other four and terminate in curious processes or short appendages called auricles. Bolina is about two inches in length, and is very delicate, transparent, and phosphorescent. Its contractile power enables it to vary in outline to a considerable extent. It has a slow undulating motion, and sometimes carries its lobes uppermost and open. Usually found associated with Pleurobrachia from Massachusetts northward.
B. septentrionalis. Found on the northern Pacific coast.
Genus Mnemiopsis
M. Leidyii. Resembles Bolina in general form; often six to eight inches in length; gregarious, thousands often being collected together; exceedingly phosphorescent.
Genus Cestum
C. veneris, Venus's girdle. This singular animal, although not an inhabitant of our seas, has its place in this group, and is shown here because of its very curious shape. In form it is flat and ribbon-like. Sometimes it attains a length of five feet, while in breadth it is but one or two inches. The mouth is midway in its length and is opposite the sense-organ or eye-spot. On each side of the mouth is a short tentacle which protrudes from a sac. Four of the swimming-plates are small; the other four extend along the edge of the body. Cestum moves by contractions of the body more than by the combs which fringe its edges. It is very transparent, with a violet hue, and is so delicate that it is difficult to capture it uninjured. Its habitat is the Mediterranean Sea. It may be seen among the zoölogical specimens in almost any museum.
Genus Idyia
I. roseola. This species has an ovate body three to four inches in height and about half as broad. Some individuals are larger. It has [pg158] an eye-spot on the upper rounded side, and at the other end a very large mouth opening into a digestive cavity, which occupies the greater part of the body. A delicate fringe surrounds the area about the eye-spot, and eight rows of cilia run from there to the oral end. It has no tentacles. Idyia is pink and especially highly colored at the spawning-time. Like other jellyfishes, their part in life is finished when they have discharged their spawn, and the first September storms break them to pieces. In July and August they are plentiful on the New England coast. They appear at the surface of the water in the hottest part of the day, but disappear entirely when the water is in the least rough or the weather is cold or the sun overcast. Their movements are slow and graceful, the long axis being carried in a nearly horizontal position. They are exceedingly voracious, feeding chiefly on other Ctenophora, and often swallowing animals as large as themselves.
I. cyanthina. This species, found on the northern Pacific coast, broadens near the center, making it somewhat vase-shaped. Idyopsis Clarkii, a similar genus, found in Florida, is globular. All these species are very beautiful, the rapid movement of the cilia giving them a brilliant iridescence.
Burrowing in sand and mud, lying under stones and in crevices of rocks, concealed in various kinds of tubular cases which are free or attached to stones or shells, crawling over the ground or seaweeds, swimming free or attached to other animals, is found in abundance a class of animals commonly known as "worms," and generally regarded as repulsive creatures unworthy of attention.
To the biologist, however, worms are among the most interesting forms of lower animal life. The amateur collector, if he stops to give them careful consideration, will probably find them unexpectedly interesting, and will be surprised to find how many varieties of them there are, and how different they are from his preconceived notion of them. Worms are varied in structure, their habits are strange, and their form and color often beautiful. Although plentiful, they are not conspicuous, but are easily found if search is made for them, and so large a class of shore animals should not be passed by unnoticed. Unusual biological interest is attached to this group because, in the different types, affinities with other classes of animals are found, suggesting, perhaps, connecting-links with higher organizations. They are the first animals to show definite bilateral symmetry, or two similar sides, and to carry the same part of the body always in front. Formerly one division, called Vermes, comprised all the worms. To-day they are separated into four divisions, or phyla. The most careless observer easily recognizes the basis of separation, for the flatworms, the round- or threadworms, the wheel-like animalcules, and the jointed worms have very obvious differences. The names given the phyla express these distinctions, the termination [pg164] meaning "worm"; the prefixes Platy-, Nemat-, Troc-, meaning "flat," "thread," "wheel," respectively; while Annulata, meaning "ringed," describes the segmented forms belonging to that phylum.
There are vast numbers of parasitic worms, which live internally or externally on their hosts, there being no animal of land or sea, of high or low degree, which is not subject to the affliction of these visitors. The parasitic worms are degenerate, some being without digestive organs, or without eyes, or without locomotor organs, and so on, as the case may be, the host supplying the missing function. The life-history of these low forms is interesting; but parasitic worms do not come within the scope of this book, and are mentioned only to mark their place in the series.
The flatworms have a flattened body, more or less compressed in the different classes. Ordinarily the body is very thin, and, when short, has a leaf-like form; when long it is ribbon-like. Some species are thick in the middle and thin at the edges. They have a dorsal, or upper, and a ventral, or under, surface; a right and a left side; an anterior and a posterior end. The anterior end is carried forward and has some of the characteristics of a head, though a distinct head is not apparent. The mouth is on the ventral surface. In some species it is in the middle of the length of the body; in others it is before or behind this point.
The flatworms are the first animals to assume pronounced bilateral symmetry. They are soft-bodied, having no supporting skeleton, and they have no segments, or divisions, such as are found in higher types, as in Annulata. They have no body-cavity, the space between the organs and the body-wall being filled with tissue. The alimentary canal has no anal aperture, the excretions being carried off by a water-vascular system consisting of branching vessels which end in minute bundles of vibrating cilia, called ciliary flames. These flames communicate with the exterior through small pores or flame-cells. Their sense-organs are eyes [pg165] and otocysts. The latter are sacs containing crystals of carbonate of lime, and their function is supposed to be that of hearing.
The flatworms are hermaphroditic, and their propagation is by means of eggs. They are numerous and very generally distributed, occurring in fresh and salt water, on land and shore, on the surface and in the depths of the sea. A vast number also are parasites and infest, internally or externally, nearly every living creature. The parasitic forms differ anatomically from the free-living worms. The internal parasites, living by absorption of the digested food of their hosts, have no digestive organs; they are also devoid of organs of sense and of defense. The external parasites, being carried about by their hosts, are without organs of locomotion.
The turbellarians are the simplest group of bilateral animals and occupy the lowest place among worms. They owe their name to the fact that they are covered with cilia, which are constantly in motion and cause a slight turbulence in the water around them.
The polyclads are found below half-tide mark on the under side of stones and on seaweeds. Sometimes they are found swimming about at night. They are leaf-like in form, one inch to two inches in length, and are very thin and delicate. They adapt themselves to the inequalities of the surfaces to which they attach themselves, and often are of the same color, and therefore are so inconspicuous that they are apt to escape notice. They move with a gliding motion over surfaces, and often swim when in search of food.
The intestine is much branched and has no anal aperture. From the mouth, which is placed in the center of the ventral surface, a pharynx, or muscular fold, is protruded in some species, which enables the worm to attach itself to and consume prey of considerable size. After digestion has taken place, the fecal [pg166] matter collects in the main intestine and is forcibly ejected by the pharynx. Numerous eyes are collected in groups on the anterior dorsal surface, or arranged around the margin of the body. The eggs are laid in shell-like cases, and cemented together in plate-like masses or in spirals, and attached to shells or stones. (Plate XLVIII.)
Genus Planocera
P. nebulosa. One half of an inch wide and three quarters of an inch long, circular or elliptical in shape; very flat and thin; olive-green on the dorsal surface, with a line of darker color on the posterior end, and whitish retractile tentacles on the back. Found creeping on under side of stones in tide-pools.
Genus Stylochopsis
S. littoralis. About one half of an inch long; changeable in form, from broad oval to elliptical; color pale green, veined with a lighter shade on the dorsal side, flesh-colored on the ventral surface; numerous eyes arranged in irregular rows near the margin and in groups in front of the tentacles, also clusters of eyes on the tentacles. Found under stones between tide-marks.
Genus Leptoplana
L. folium. Body flat; margin thin and undulated; shape leaf-like, but changeable; about one inch long and one half of an inch wide; color pale yellow, veined with a deeper shade; eyes in four groups near the anterior end.
The triclads are divided into three groups: those of the fresh-water ponds and streams, those of the land and sea, known as planarians, and those of the sea. The planarians are the most interesting worms in the order. The triclads differ from the polyclads in being elongate in form and in having the intestine in three branches instead of in many. The mouth is midway in the length of the body, on the ventral side, and from it protrudes a pharynx, which is cylindrical or bell-shaped, and is capable of great dilatation. With the pharynx the worm, which is wholly carnivorous, envelops other worms, crustaceans, or any animal food. Several species are found on the under side of stones in tide-pools.
Genus Planaria
P. grisea. Oval or elliptical in form; anterior end truncate; posterior end rounded; color yellow or gray, with a light stripe; two black eyes surrounded with white; length one half to three quarters of an inch; width about one eighth of an inch. Found under stones between tide-marks.
Genus Procerodes
P. frequens. One eighth of an inch long; brown or black above, gray below; has two kidney-shaped eyes; active and abundant. Found under stones near high-water mark.
Genus Bdelloura
B. rustica. Body milk-white, smooth, thin. Found on Ulva latissima (sea-lettuce).
B. candida. Parasitic on the gills of the horseshoe-crab.
Genus Fovia
F. Warrenii. Bright red, narrow, oblong. Found on eel-grass.
Minute, active worms found among the red seaweeds. They are brown in color, and are marked by one or more transverse white bars.
The nemerteans are long, narrow, flat, smooth worms, and vary from one half of an inch to many feet in length. They are exceedingly contractile, and when alarmed can shrink to less than half their normal length. They are very generally distributed, and are to be found between tide-marks, in loose coils like a string, under stones on sandy and muddy shores. The very long species, like Lineus marinus, are solitary, but other smaller species are gregarious, many worms being coiled together in tangled masses. Some species are to be found in empty shells, and others live among the seaweeds. They are very slimy, the epidermis secreting an abundance of mucus, and they can often be tracked by the trail of slime they leave behind them. This mucus sometimes hardens, forming for some species a tubular [pg168] covering; others remain naked. All are covered with vibrating cilia, which is a universal feature of flatworms. In color they may be white, yellow, green, red, purple, etc., and sometimes they are banded or striped with a contrasting color. The ventral is usually lighter than the dorsal surface.
The principal characteristic of the nemertean worms is a long thread-like organ, known as the proboscis. This lies in a sheath along the center of the dorsal surface, and is quickly thrown out to a great length, and as quickly completely withdrawn within the body. The proboscis is slender, hollow, muscular, and full of nerves. It reaches the outside through a pore at the anterior end of the body, and has no connection with the alimentary system. It is used as a feeler and as a weapon. Some species have a sharp spine at the end of the proboscis, others have stinging-cells. The proboscis is sometimes so forcibly ejected that it breaks off, in which case it retains its vitality for some time, and seems as if it were itself a worm. A new proboscis is quickly grown by the worm to take the place of a lost one. The head is a little broader than the body, and has eyes arranged in one or several pairs on each side. The mouth is on the ventral surface, near the anterior end, has thick lips, and is very dilatable. Through the mouth the animal ejects a part of the esophagus and envelops its prey, which is often of considerable size. Chætopod worms they often swallow whole; the soft parts, after being digested, are carried off through the regular passages, ending in the ciliary flames (page 164), while the indigestible parts are ejected at the anus. Often the spines and bristles find their way out by perforating the intestine and the body-wall, without apparently doing the worm any injury. The perforated parts quickly heal.
These worms have the strange power of regenerating lost parts; mutilated portions are soon repaired. The anterior end, when severed from the rest of the body, grows again into a complete individual, while the posterior end continues to perform part of its functions and retains its vitality for a considerable time before dying. One species, Lineus sanguineus, is capable, after being broken in pieces, of regenerating each section into a perfect worm. [pg169]
The nemerteans are carnivorous, voracious, and often cannibalistic. They will live for some time in confinement, losing, however, their bright color, and the smaller worms will gradually disappear, as they are devoured by the larger ones. The mode of locomotion varies with the order. Some species attach their long proboscis to a distant object, then drag the body to it; some glide rapidly along by means of the muscles of the body and the cilia which cover it; others swim. The swimming forms have thin edges which have a wave-like motion, and this, together with a lateral movement of the tail, propels them through the water. In some species the worm develops directly from the egg; others pass through a larval stage before reaching maturity.
Genus Tetrastemma
T. arenicola. Dark flesh-color or purplish; slender, cylindrical, four to five inches long when extended; head changeable in form and partly distinct from body because of slight constriction at the neck. It lives in sand at low-water mark.
Genus Nemertes
N. socialis. Individuals very slender, five to six inches long when extended; color brown or black, a little lighter underneath; three or four eyes in lines on each side the head. It is abundant under stones on rocky shores, many coiled together, forming large masses.
N. viridis. Color olive-green or brown, crossed by faint pale lines; body changeable in form; when extended, six to eight inches long, one eighth of an inch or less in breadth; row of dark eyes on each side of flat head. Common under stones between tide-marks on northern rocky shores.
Genus Meckelia
M. ingens. One of the largest nemertean worms; found on sandy and muddy shores near low-water mark. The young, from several inches to a foot long, are common. When full-grown some attain the length of twelve or thirteen feet, and are an inch in breadth and quite flat when extended, but can contract to two or three feet in length, and are then nearly cylindrical. This worm, although so soft, penetrates the sand with great rapidity. Its head changes shape constantly and assists the proboscis when burrowing. It is also able to swim. Its color is yellowish or flesh-color, with whitish edges and a central band.
M. rosea. The largest specimens are six to eight inches long and one quarter of an inch broad; lives in burrows on sandy beaches; color red or pink; often covered with sand, which adheres to the mucus which the worm secretes. [pg170]
Genus Cerebratulus
C. angulatus. Olive-green, with light dorsal stripe.
Genus Cosmocephala
C. ochracea. Two to three inches long when extended; gray or yellowish-white, and mottled by the internal organs showing through the translucent body; line of lighter color down the back; anterior end often orange-colored. It is common near low-water mark under stones and in the dead tubes of Serpula.
Genus Polina
P. glutinosa. One to two inches long; color orange or light yellow, with a faint line of deeper color down the center of the dorsal surface; very slimy; eyes numerous, in oblique lines on the head. Found in tide-pools on algæ.
The worms of this phylum have the general name of roundworms, which distinguishes them from the flatworms of the preceding division and from the segmented worms of the Annulata. The body is elongated, cylindrical, smooth, and pointed at both ends. With few exceptions, they are parasitic.
A few of the nematode species are free, living under stones and among seaweeds at about low-water mark.
Genus Pontonema
P. marinum. Slender, white, smooth, active, cylindrical; constantly coiling and uncoiling itself.
The name of this phylum expresses the principal characteristic of the group of worms which have elongated bodies composed of series of short parts, or ring-like divisions. Each one of these segments contains a separate and similar set of internal organs. [pg171]
The annelids are divided into four classes, one of which, the Gephyrea, has not the characteristics which distinguish the group. The classes are easily recognized by conspicuous features. Some have bristles; others have scales; others have tentacles around the head and inclose themselves in tubes. Many are highly colored, and all are of great interest to the naturalist from the diversity of their habits, form, and structure, and from the analogies they bear to other and higher types of animals.
The annelids are the highest type of worms, their organs having attained more special functions. The sense-organs of eye and ear are more developed, and the nervous system has distinct centers, or ganglia, the first and largest ganglion being a part of the head. They are found in abundance everywhere. Some species grow to the length of one foot or two feet. Some are carnivorous, others vegetarian, and many are mud-eaters, swallowing sand and mud for the sake of the organisms they contain. They themselves are food for fishes, which devour them in vast quantities, rooting them out of their burrows or capturing them at night, at which time they swim about.
The bristle-worms. This class of worms has bunches of bristles on both sides of each segment of the body, which serve as organs of locomotion, or bristle-feet. The bristles emanate from outgrowths of the body known as parapodia, which are practically limbs. The parapodia are sometimes divided into distinct lobes or branches. The bristles are of various shapes and often of brilliant color. They are usually horny, sometimes simple, sometimes divided into joints, and vary in shape in different genera. The parapodia have, besides the bristles, a second set of [pg172] hair-like appendages, called cirri. These are sense-organs and also have a respiratory function. The cirri too vary in shape in different genera. Generally they are hair-like, but sometimes conical; again they are broadened into scales, as in the Aphroditidæ.
The body-cavity in chætopod worms is divided into a series of chambers or segments. These divisions seem on the exterior like constrictions, and give the body the appearance of a series of rings. The internal organs are repeated in each segment, so that each of the latter contains a portion of the alimentary canal, a pair of nephridia, a pair of nerve-ganglia, and blood-vessels which connect the main blood-vessels running along the dorsal and ventral surfaces. The alimentary canal runs through the body, but is constricted at each joint. The nephridia are curved tubes, which are excretory organs, opening to the outside and carrying off the waste products which have passed into the fluid of the body-cavity.
The chætopod worms have a well-developed nervous system, beginning with a two-lobed ganglion forming a brain and head, then extending through the worm in a double ventral chain and series of ganglia. They have also a blood-vascular system. The blood is either colored or colorless. Sometimes it is a bright red or green, and is often visible through the body-wall. The circulation is effected, not by means of a heart, but by wave-like (peristaltic) contractions of the dorsal blood-vessel. The body is cylindrical, but in many cases is somewhat flattened. There are two layers of muscles, one of which encircles the body, while the other extends parallel with its length. Respiration is effected by gills, which may be simple, hair-like appendages to the parapodia, or branched, or comb-like in form. Sometimes they are confined to the middle segments, as in Arenicola; sometimes to the segments near the head, as in Tubicola; or they may be extended over the whole dorsal surface.
The polychæte worms have one or two well-developed parapodia, or limbs, on each side of every segment of the body, and on each [pg173] parapodium is a bunch of bristles, or chætæ. There are hundreds of species of this class of worms, the species being based on the shape and the lobes of the parapodia, the relative length of the cirri, the form and arrangement of the chætæ, and so on. They are abundant on the shore everywhere, but abound where rocks and stones afford them some shelter. Many burrow in the sand and mud. In doing this the worm eats his way into the hole, swallowing the mud and sand. He assimilates the organic or vegetable matter the mud contains, and ejects the rest in cylindrical coils, known as castings, which lie in heaps at the mouth of the burrow. By these castings they may be traced. Others secrete tubes.
The polychæte worms are divided into Errantia, which are wandering, free-swimming forms, and Sedentaria or Tubicola, which live in tubes permanently. These distinctions are not strictly correct, since some species of errant polychætes form tubes (Eunicidæ), and some Sedentaria form no tubes.
Many polychætes are beautifully colored, some in vivid reds and greens, with various markings; some are iridescent; some are phosphorescent.
ORDER ERRANTIA
Carnivorous, free Polychæta, with protrusible pharynx armed with a horny jaw. "They are active, fierce beasts of prey."
Family SYLLIDÆ
This family is the highest in organization of the worms. They are small, the majority being less than an inch in length, and many are minute. They are often highly colored. Many have long cirri on the feet; some have alternation of generation. They are common everywhere along the coast, but are not seen unless searched for. Sponges sometimes are alive with them. They are interesting subjects for microscopic study.
Family APHRODITIDÆ
The scale-bearing annelids. This family of worms is distinguished from all others by having scales on the back. The scales, called elytra, are flattened dorsal cirri carried on the upper parapodia, [pg174] and generally on alternate segments and in a double row down the back. The elytra are the breathing-organs, and, although of a horny texture, are richly supplied with nerves. The worms are short and have a large protrusible pharynx armed with a double pair of horny jaws.
Genus Polynoë
The species of Polynoë are determined by the number of scales they bear. They have a flattened short body with nearly parallel sides. The bristles are of a bright golden color. The proboscis is large and has four powerful jaws at the end and a circle of papillæ at the top. They are sluggish in movement and are found under stones and in the crevices of rocks. When disturbed they roll themselves into a ball.
P. squamata. Twelve pairs of rough scales; color sandy-brown, speckled; one inch to one and a half inches long; the broad, oval scales overlap and entirely cover the body and head. Some Polynoë when disturbed throw off every scale. Very common north of Cape Cod.
P. sublevis. Twelve pairs of smooth scales; usually grayish-brown in color, speckled with dark spots; iridescent; last pair of scales more slender than the others; length one and a quarter inches, breadth about one quarter of an inch.
Genus Harmothoë
H. imbricata. Sixteen pairs of smooth scales; variable in color; usually gray, speckled, or striped.
Genus Aphrodite
A. aculeata. This polychæte, sometimes called the sea-mouse, is one of the most beautiful of worms. It is brightly iridescent in color, from its setæ, which form a fur-like coating over the dorsal surface. It has fifteen pairs of scales, but they are hidden by the numerous setæ. These bristles cover its sides and back. Some are coarse and nearly an inch long, with sharp points, and are barbed near the ends. They curve over the back like the quills of a porcupine. The body is three to six inches long. It is broadest in the middle and tapers to a point. They live in mud below tide-mark, and may be found washed upon the beach after storms. [pg175]
Family PHYLLODOCIDÆ
These animals are commonly known as "paddle-worms," on account of having leaf-like cirri, which they use in locomotion. The head is long and bears four pairs of short and four pairs of long tentacles. The body is long and depressed, sometimes two feet in length, usually eight to twelve inches long. The general color is bright green and iridescent. Found in tide-pools. Specimens are often found by digging in sandy mud, or they may be obtained by placing old shells and other material in a dish of sea-water. When the water becomes a little stale, the worms of this and other families make their way to the sides of the dish, where they secrete a colorless slime which holds mud or any light matter that it may come in contact with. In this condition, when lifted or disturbed, they crawl rapidly out of the slime, and show to good advantage their elongate body, which is often beautifully colored.
Genus Phyllodoce
P. gracilis. Three inches or more long and one sixteenth of an inch wide; large proboscis, with twelve longitudinal rows of prominent [pg176] projections on the swollen base, its terminal end smooth, with a circle of round projections at the orifice; color green, with a row of dark spots down the center of the dorsal surface and a fainter line of spots on each side at the base of the parapodia. Found on the New England coast.
Family NEREIDÆ
Genus Nereis
Among the most common of the polychæte worms is the genus Nereis, various species of which are found in all parts of the world. They are abundant under stones, among seaweeds, and living in burrows between tide-marks. They are active, fierce, and voracious. Some attain a length of eighteen or more inches. They are commonly known as "clam-worms," and are used by fishermen for bait. Nereis has a distinct head, consisting of two parts. One, the prostomium, bears on its upper side four eyes and a pair of short, conical tentacles, and on the lateral sides a second pair of processes called palps. The palps are more conspicuous than the tentacles, and consist of two parts, a large base and a small terminal point, the latter capable of being withdrawn. The palps are sense-organs and perhaps test the food. The second part of the head, or peristomium, bears on the sides four pairs of long tentacles which are used as feelers. The mouth is on the ventral side, and through it Nereis throws out its pharynx, which contains a horny, notched jaw. It seizes its prey with this jaw, which, with the pharynx, is then withdrawn and tears the food apart, acting like a gizzard. The body of Nereis is rounded above and nearly flat below. Each of the segments has a pair of parapodia, bearing a bundle of bristles and cirri. The last segment of the body is elongated, cylindrical, and without parapodia, but has on the end a pair of long cirri, which give the appearance of a divided tail. Each segment of the body, except the head- and tail-segments, contains a pair of excretory tubes (nephridia), ganglia of nerves, and a portion of the intestine and of the vascular system. There are circular muscles by which the worm can diminish its diameter, longitudinal [pg177] muscles in four bands, and muscles to move the parapodia. Breathing is carried on over the whole surface of the body, and especially in parts of the lobes of the parapodia called gills. Its sense-organs are eyes, palps, tentacles, and cirri.