O. aculeata. This is a common species, found in shallow water on the North Atlantic coast. A similar or perhaps identical species occurs on the North Pacific coast. It is spotted purple or variegated in color. The upper surface of the body is covered with plates variously arranged, sometimes in the shape of a star, and each one is surrounded with small spines. The under side of the egg-sacs is covered with small spines. These sacs open by slits on each side next the arms, and have a rounded appearance, bulging out between the arms. The arms, which are long and attenuated at the ends, have on the upper side transverse oval plates surrounded by a border of flat, roundish granules. Sometimes the plates are divided into two or three pieces, when they are similarly bordered with granules. The arms are fringed with rows of thick, compressed, obtuse spines, generally six in each row. The under sides of the arms have large quadrangular plates slightly separated from one another and extending across the whole surface in regular, even rows. (Plate LV.)
Genus Amphiura
A. squamata. This very delicate species, found on shelly bottoms below low-water mark from New Jersey northward, has a body less than one quarter of an inch in diameter, with arms two inches or more [pg216] in length and thread-like in size. These long, slender arms have, on both the upper and under surfaces, a row of overlapping plates, and are fringed with small spines, three in a row. The color is gray or whitish, sometimes marked with darker gray or brown. (Plate LV.)
Genus Ophiocoma
O. riisei, O. æthiops, O. Alexandri. These animals have long spines on the sides of the arms, which give them a bushy appearance. The surface of the body is granulated, but the arms are covered with wide plates. Their color is brown above and light beneath. O. riisei is found at Key West, the other two species on the coast of Lower California. (Plate LV.)
Genus Ophiothrix
O. angulata. Body covered with short, rough spines; egg-sacs conspicuous and extend like lobes between the arms; rays narrow and thickly beset with long spines, which are serrated on the edges and ends. Found on the Florida coast. (Plate LV.)
| PLATE LV. | |
|---|---|
| Astrophyton. | Ophiopholis aculeata. |
| Ophiocoma æthiops. | Ophiocoma Alexandri. |
| Ophiothrix angulata. | Amphiura squamata. |
The shell of a sea-urchin consists of many calcareous plates, or ossicles, fitted closely together and forming a continuous exoskeleton. The plates are so united that externally the marks of juncture are not perceptible, but on the interior the shape of these plates is well defined. In examining such a shell, or test (they abound on the beach), it will be seen that its surface is covered with numerous hemispherical projections or knobs, which are grouped in double rows and run in meridional lines from one pole to the other of the more or less spherical body, separating it into ten divisions. Five of these divisions have perforations, or small pores in the plates of the shell, and are called the ambulacral zones or areas, because through these pores pass the small tubes, in the living animal, which connect the tube-feet, or ambulacra, with the radial water-canals and the ampullæ (see page 206). The wide spaces between these double rows of pores are called the interambulacral zones or areas. The ten spaces diverge from the peristome, or soft part around the mouth, in the center of the lower surface, and converge in the small area at the top or aboral side. In the center of this small circular dorsal space is the excretory opening, and surrounding it are ten plates, five of which have openings into the egg-sacs. One of them is larger than the others, and is modified to form the madreporic plate. The other five plates have eye-specks. The ambulacral zones terminate at these ocular plates.
The numerous spines which cover the animal are of three [pg219] kinds, and proceed from the knobs on the exoskeleton, over which they fit, forming ball-and-socket joints, which enable them to move in any direction. The long spines are ribbed, and seem to have no other function than that of protection. The second set, the pedicellariæ, are very peculiar small organs scattered over the surface in great numbers, and consisting of a head bearing three bill-like blades mounted on a long, flexible stalk. The office of some of the pedicellariæ is to remove waste from the excretory opening; this is passed down regular lines and dropped into the water, thus keeping the body clean. Others are constantly opening and shutting their forks, reaching in all directions and grasping and removing anything which may have become entangled in the spines. They also capture floating bits of seaweed, which they drag over the body to conceal it. A third set of projections are the sphæridia, small globular bodies said to be connected with perception.
The spines vary greatly in size, number, and form in different species, and are such conspicuous features as to make the identification of species easy. In some the spines are solid and fluted; [pg220] in others they are hollow, sharp, and brittle; again in others they are short and silky, or very long and serrated, and so on. In one species they are so broad and flat as to resemble little sails. (See Dorocidaris.) (Plate LVI.)
The mouth, over which five long teeth project, is a part of Aristotle's lantern, which forms a curious and prominent feature in the center of the lower surface. Ten tentacles, like large tube-feet without suckers, lie around the mouth. The alimentary canal, starting in Aristotle's lantern, winds in two and a half coils around the inside of the shell, supported by mesenteries, and terminates in the excretory opening on the aboral surface. The sea-urchin has also a water-vascular system similar to that of starfishes (page 206). When the tube-feet are distended they project beyond the spines, and enable the animal to move slowly about; but sea-urchins are less active than starfishes, and although they are so well protected by spines and have few enemies after maturity, they lie in sluggish idleness in secluded places, and for further concealment often cover themselves with seaweeds or stones.
The sea-urchin has a nervous system, which starts in a ring around the mouth, ramifies through the body, and terminates in the eye-plates. The tube-feet and all the spines are under nervous as well as muscular control. Egg-sacs lie under the apex of the shell and open by separate ducts into the five plates on the small upper disk. Through these the eggs are discharged into the water, where they become free-swimming larvæ, called Pluteus. This immature sea-urchin (Pluteus) undergoes several curious transformations in the course of its development, and does not in any way resemble the mature animal. In spring the apical disk of the females will often be found covered with orange-colored ova, and that of the males with white sperms. In the growth of the animal, in its mature form, the shell enlarges by accretions of lime on the individual plates, or ossicles, of the exoskeleton, and by new plates formed around the apical disk. Sea-urchins are compared to starfishes folded over, the eye-specks on the ends of the rays meeting in a small area around the excretory opening, the ambulacra following spherical lines and leaving the mouth, as before, on the ventral side. [pg221]
The Echinoidea present great differences in shape, being more or less spherical, oval, discoid, and heart-shaped. These variations are associated with the differences of internal structure, the openings of the digestive tract being at the opposite poles in the spherical and oval forms, but excentric in the disk- and heart-shaped species. The sea-urchins are grouped in three orders in accordance with these variations. All are characterized by the absence of arms, by having the calcareous plates immovably united to form a firm test, and by the great development of the movable spines upon the plates.
Sea-urchins are sometimes called sea-eggs, perhaps from their shape, but possibly from the edible quality of some species, which are eaten by the natives of the shore, who take them at the spawning season, when the egg-sacs are distended. They are gregarious, and frequently are so crowded together as literally to pave the surface of rocks and the bottoms of tide-pools in sheltered places. The following is quoted from A. Agassiz: "Many of the Desmosticha along coasts exposed to the action of the waves live in cavities which they hollow out of the solid rock. This they do, not by means of any solvent, but by mere mechanical action. They chisel out with their teeth the solid rock by incessant turning round and round, and keep their cave, where they are frequently prisoners for the rest of their existence, up to the size required by the growth of their test and spines, by constant gnawing. On the coast of California the common Strongylocentrotus purpuratus occurs in this way. We find long tracts of shore, where this sea-urchin is common, completely honeycombed and pitted by cavities and depressions in which they seek shelter against the powerful surf continually beating against the rocks. The same species does not excavate in sheltered places, where the sea-urchins can find protection between the interstices of large fragments of rock or ledges more or less sheltered from the more direct action of the open sea."
Sea-urchins in cavities of granite rock, where the openings are too small for the animal to get out, are to be seen in thousands on the coast of France at Croisic, Lower Loire. Spines of large sea-urchins are used as slate-pencils by the missionaries in the Pacific Islands. [pg222]
Genus Cidaris
C. tribuloides. Similar to Porocidaris sharreri, but with thicker and stouter spines. Found from South Carolina to Brazil.
Genus Dorocidaris
D. papillota. A deep-water species which occurs off Chesapeake Bay and southward. It has slender spines with distinct longitudinal rows of serrations, and the spines are grouped in rosette-like forms over the small spherical body.
D. Blakei. This species is very peculiar in having broad, fan-shaped spines; vermilion in color. Found in deep water in the Bahamas and West Indies. (Plate LVII.)
Genus Porocidaris
P. sharreri. This species occurs, in deep water, off the coast of North Carolina and thence southward to the West Indies. The shell is light greenish-pink. The spines are white, with brownish-pink at the base, pointed, three and a half inches long, and surrounded at the base with small, flat, triangular, secondary spines. (Plate LVII.)
Genus Arbacia
A. punctulata. A small species found in shallow water on shelly and gravelly bottoms from Massachusetts to Mexico, and common in Long Island Sound. The shell is about one inch in diameter; the spines are rather thick and one half to three quarters of an inch long. The color varies from deep violet—almost black—to straw-color, and the spines are tipped with brown. The South Carolina species are usually brick-red in the bare interambulacral spaces, with darker sutures, and spines tipped with same color. The animal walks by means of its spines, with a tilting motion, and advances quite rapidly. (Plate LVII.)
Genus Cœlopleurus
C. floridanus. This beautiful sea-urchin is taken on the Florida reefs. The very brittle spines are one to four inches long, and are banded with carmine and white. The shell has zones of light chocolate-color alternating with orange and yellow.
Genus Diadema
D. setosum. Spines very brittle, and from one to two and a half inches long; jet-black. Found on the Florida reefs. (Plate LVII.)
| PLATE LVII. | |
|---|---|
| Porocidaris sharreri. | Dorocidaris Blakei. |
| Arbacia punctulata. | |
| Diadema setosum. | Strongylocentrotus franciscanus. |
In this family the ambulacral plates have several pairs of pores.
Genus Echinometra
E. subangularis. This species, which ranges from South Carolina to Brazil, and is also found in Bermuda, is common on mud-flats and is easily distinguished by its oblong or elliptical shape. Its shell is about three inches long in its widest portion. The spines are one half of an inch to one inch long, thick at the base and tapering to a point. The color is dark purplish-green to deep violet—almost black.
Genus Strongylocentrotus
S. drobachiensis. This sea-urchin (which bears, perhaps, the longest name in technical nomenclature and has no other, unless that of "sea-egg," which is applied indiscriminately to all sea-urchins) is a very common species in shallow waters of the northern temperate zones. It extends as far as New Jersey on the Atlantic and to the State of Washington on the Pacific coast. Although it is found as far south as New Jersey, it is there rare and small; but farther north, especially on the coast of Maine, it is exceedingly abundant. It is green or greenish-purple in color, and resembles somewhat a large chestnut-bur. The body is circular, somewhat depressed (but of variable thickness), and about two inches in diameter. The spines are moderately slender and longitudinally striated. It feeds partly on diatoms and other small algæ, which it cuts from the rocks with its sharp teeth. It also devours dead fishes, bones and all, and in return is swallowed whole by the wolffish and other large fishes. It moves by means of the tube-feet on its oral surface, slowly dragging itself along, and frequently is seen with seaweed, a stone, or some other substance on its back, which it places there with its pedicellariæ for the purpose of concealment.
S. purpuratus. The common purple sea-urchin of the west coast, from Sitka to Lower California, found in abundance on the rocks just beyond low-water mark. It is about one and a half inches in diameter, with rather thick, pointed, and fluted spines.
S. franciscanus. This is the largest species of the west coast, the shell measuring sometimes five inches across, and the thick spines one and a half inches in length. The tubercles on the naked shells are very prominent, and the zones are very clearly marked. It is purple in color and is often found in great quantities at low-water mark. It ranges from Alaska to Lower California. (Plate LVII.)
In this family the ambulacral plates have but three pairs of pores. [pg224]
Genus Echinus
E. gracilis. This is a deep-water species, which occurs from Cape Cod southward. The shell is nearly spherical, but is a little depressed on the oral side, and has twenty bands of color, alternately green and white. The spines are short and thin.
Genus Toxopneustes
T. variegatus. This is the common species of the Southern States, from North Carolina southward, and is found in shallow water in protected places. The shell is nearly globular; the spines vary in thickness and color, some being long, slender, and greenish, while others have stout and blunt spines of a yellowish or violet tint.
The animals of this order, commonly known as sand-cakes or sand-dollars, are flat and circular like disks. Sometimes they are cut at intervals on the margin; again they have slits through the body (lunules). They have a well-marked star-shaped figure on the dorsal surface. This figure is formed by the ambulacra, or tube-feet, which run in five rounded or petal-shaped lines on the under surface. The mouth, in Aristotle's lantern, is in the center of the somewhat concave ventral surface, the petal-like ambulacral zones meeting at the central space. The excretory opening is on the margin of the disk, at a point between two of the sections of the star-like figure. This marks the posterior part of the body, while the opposite arm of the star marks the front or anterior end. The spines are very fine and silky, and are spread abundantly over the whole animal. Clypeasteroids are mainly found in sand considerably below low-water mark, though some species thrive where they are exposed to the surf on open sandy beaches.
Genus Clypeaster
C. ravenellii. This species occurs in deep water from South Carolina southward. The disk is about four inches in diameter, and is raised [pg225] in the center into a large cone. The ambulacra run down the sides of the cone in straight lines, and around the base is a depressed area which emphasizes a thick border which extends around the scalloped margin. The color is light yellowish-brown. (Plate LVIII.)
Genus Echinanthus
E. rosaceus. This is a large species, oblong in shape, about four to five inches across and much rounded on top, the body being about two inches thick. The ambulacral zones are depressed, leaving prominent elevations which make a very conspicuous figure on the top. The color is light chocolate-brown. Found close to the shore off the coasts of Florida, South Carolina, and the West Indies.
Genus Echinarachnius THE SAND-DOLLARS
E. parma. This species, the shells of which are very common objects on sand-beaches from New Jersey northward, is generally known as the sand-dollar. The animals have flat circular disks about three inches in diameter. The ambulacral zones, in five petal-like lines, form a distinct figure on the upper surface. The mouth is in the center of the ventral surface, and the excretory opening is on the edge of the disk. In life they are covered with short, fine, silky spines, which seem like hair, and are purplish-brown in color, but turn green when taken from the water. The sand-dollars are exceedingly abundant off Nantucket Shoals, where the bottom seems paved with them. They are eaten in great numbers by flounders, cod, and haddock. When put in alcohol they stain it a dark color. Fishermen prepare an indelible ink by grinding to powder these animals and mixing it with some liquid. This species is also found on the northern Pacific coast.
E. excentricus. This is the common sand-dollar of the Pacific coast. The disk, instead of being circular as in E. parma, is somewhat straight across the posterior end, and the posterior ambulacral zones are shorter than the other three. The upper side of the disk is raised, forming a cone-like elevation, the apex being the center of the figure.
Genus Mellita
M. testudinata. The disk is rounded in front and straight in the back. Four long, narrow lunules, or cuts, occur on the sides in line with the ambulacral, petal-shaped zones, but do not extend quite to the edge of the disk; and a wide lunule occurs in the interambulacral space [pg226] of the posterior end. The three anterior zones are shorter than the posterior pair. On the upper side of the disk the spines all turn toward the periphery. The color of the living animal is greenish-blue. It is very abundant from Cape Hatteras southward in shallow water, and the shells are sometimes found as far north as Cape Cod. (Plate LVIII.)
Genus Encope
E. michelini. Ambulacral zones unequal in size, the posterior pair usually longer than the others; lunules like notches in the margin, with a large one opening between the posterior ambulacral zones nearly in the center of the disk; disk rounded in front and square at the back. Common on the coasts of southern Florida and the Gulf of Mexico in shallow water. (Plate LVIII.)
The Spatangoidea, or heart-urchins, have heart-shaped or thick elliptical bodies. The mouth and excretory opening are both away from the center and on the ventral side. These animals seem deformed, so much are they out of symmetry and so different in outline from the other orders of the class. The ambulacral zones are in circles, or petaloid in outline, as in cake-urchins, but are not continuous, and the anterior one is usually unlike the others and frequently without pores. The entire body is covered with spines, and these are the chief organs of locomotion; the greater part of them turn backward, giving the living animal the semblance of a porcupine. The mouth is protected by a projecting plate, but Aristotle's lantern is absent in this order. The anatomy is in general the same as in the other orders, but the organs are turned in conformity with the inclosing shell. Most of these animals bury themselves in sand or mud and live in deep water; a few only are littoral species.
Genus Moira
M. atropos. Size about one inch by one and a half inches, and one inch thick; color yellowish-white, with brown spines. Found from North Carolina to Florida, from the shore to deep water.
| PLATE LVIII. | |
|---|---|
| Clypeaster ravenellii. | Mellita testudinata. |
| Encope michelini. | Test of Metalia pectoralis. |
| Lovenia cordiformis. | |
L. cordiformis. About one inch by one and a half inches thick; reddish in color; resembles a little porcupine. Found on the southern California coast. (Plate LVIII.)
Genus Schizaster
S. fragilis. One and a half by two inches in size, and one inch thick; color brownish. Lives in deep water off the eastern coast.
Genus Metalia
M. pectoralis. A very large heart-urchin, found on the southern coast of Florida and in the West Indies in shallow water. It is, perhaps, the largest species found, being six to eight inches long and proportionately wide and thick. The shell is thin, more or less elliptical, and densely clothed with long reddish-gray spines. (Plate LVIII.)
Genus Brissopsis
B. lyrifera. A beautiful deep-water species, found off the coasts of Florida and the Gulf of Mexico. It has a red body with pale-yellowish spines. In size it is about two by two and a half inches, and is thickest on the posterior end. It is thickly clothed with long curved spines, some of which form two long tufts in the back. [pg228]
The holothurians, or sea-cucumbers, although in appearance quite unlike starfishes and sea-urchins, have the characteristic ambulacral zones and other features of the group. In form they are cylindrical, and, when the tentacles and tube-feet are retracted, resemble fat worms; when fully expanded they are somewhat like sea-anemones, the tentacles forming a rosette-like top. The walls of the body are tough and muscular, with small calcareous deposits or spicules of various shapes in the skin. The mouth is at one end, the excretory opening at the other, and along the body are double rows of tube-feet. Often instead of tube-feet, or together with them, are conical processes without suckers. The ambulacra, when arranged in regular zones, are used for locomotion only in the lines running from the madreporic plate. In some species three of the zones are near together, and form a kind of sole on which the animal creeps; again the tube-feet are wholly suppressed, as in Synapta. Besides progressing by means of these suckers, the holothurians move, as do worms, by the extension and contraction of the body. The inner surface of the tough membrane inclosing the body is lined with powerful longitudinal and transverse muscles, by means of which the creature contracts and lengthens its body and changes its form in a wonderful manner. Around the mouth are tentacles, which are often much branched and are used as organs of touch and smell, and sometimes have an ear-sac at the base. From the mouth the food-canal, making one long coil, extends to a chamber [pg231] (cloaca) at the other pole. The cloaca gives off a pair of much-branched respiratory trees, which are constantly supplied with water by the contractions of the cloaca. At the base of one of the respiratory trees are singular structures known as Cuvierian organs. They are numerous, viscid, glandular tubes, which the animal can throw out, and which will adhere closely to almost anything. The holothurian has a water-vascular system, the madreporic plate being near the mouth, but not opening to the outside, and a nervous system which starts from a ring which lies around the mouth. The egg-sacs are branched tubes, often highly colored, which open to the outside, close to the wreath of tentacles surrounding the mouth.
The larvæ, when free-swimming, are called Auricula. In the deep-water species, Cucumaria crocea and Psolus ephippiger, the eggs, when discharged, and the young are carried on the back of the mother. In Cucumaria lævigata there is a brood-pouch, while in Synapta viviparia the young develop in the body-cavity.
The holothurians have the singular power of ejecting the whole of their internal organs and of growing them again in case they escape the enemy they have endeavored to elude by this strange method. They also turn themselves inside out, as it were, as if from nausea, when confined in water too stale for their uses. Often the viscera are ejected through holes in the sides of the body broken by violent muscular contractions.
Holothurians are generally distributed through all seas, but are congregated in greatest numbers in Eastern seas. Their habitat extends from shallow to very deep water. They are found in tide-pools, on rocks, and in sand or mud. Like worms, they live on organic particles contained in mud and sand, which they take into the gullet and pass through the alimentary canal.
Genus Thyone
T. briareus. This is a large purple holothurian, found in shallow water from Texas to Cape Cod. It is four to five inches long and one inch or more thick, purple in color, and thickly covered over its whole surface with prominent papillæ. [pg232]
Genus Pentacta
P. frondosa. This animal is commonly called the sea-cucumber, and the popular name somewhat expresses its form, but it has the power of changing its shape in a most surprising manner. Sometimes it will be nearly globular, again long and thin, or it may be constricted like an hourglass. When at rest the body is ovate and somewhat pentagonal. On the angles are double lines of suckers, and in the interambulacral zones are a few scattered false ambulacra. The surface is nearly smooth, very dark purple on one side, and inclined to whitish on the other. Ten much-branched tentacles surround the mouth. The animal, when grown and expanded, measures fifteen to eighteen inches in length. This species is found throughout the whole length of both the east and the west coasts. It is very plentiful on the Maine coast in tide-pools and on the rocks at low-water mark. The genus ranges over the greater part of the globe. The tough muscular body is said to be edible, tasting somewhat like lobster, or trepang (Holothuria edulis), which is found on coral reefs in Eastern seas and is much valued as food by the Chinese. The internal organs of P. frondosa are highly colored, making its anatomy easy to trace. The muscular system is plainly defined.
Genus Lophothuria
L. fabricii (Verrill), Psolus fabricii (Düben), Cuvieria squamata (D. and K.: Agassiz). The body in this species is covered with rounded overlapping scales and numerous granulations, and when it is retracted is about two and a half to three inches long and about one inch thick. [pg233] Rows of tube-feet lie near together, on a flat under surface, and form a kind of sole on which the animal creeps. The oral end of the body is a little raised and bears ten tentacles; these tentacles are profusely and finely branched, and when expanded are about as long as the body. The aboral end is obtuse and a little raised. Around the oral and anal openings the scales are grouped, forming circles in those regions. This holothurian is bright red in color, and when expanded is a beautiful object, perhaps the most attractive in appearance of any in the class. When retracted it has the aspect of an ascidian, and for a time was supposed to belong to that group. It is found on the New England coast on the under side of large shelving rocks.
Genus Synapta
S. tenuis. This curious animal is long and slender, and so transparent that its internal organs are clearly visible. Around the mouth are a circular tube and a wreath of twelve branching tentacles. There are no ambulacra. Little spots scattered irregularly over the surface show, when highly magnified, small warts, each one of which has a calcareous projection shaped like a little anchor. By means of these anchors and by the contractions of its body the animal moves through the mud or sand in which it lives, near low-water mark. The sand is collected into rings at the oral end and pushed downward until the whole animal is inclosed in a sand-tube. When empty Synapta is white and transparent, and the digestive canal may be seen wound in a spiral throughout its length; but when gorged with food, sand, pebbles, and shells can be distinctly seen filling the food-canal, and the body then has a dark-gray color. Synapta grows to a length of eighteen inches or more, but is constantly breaking pieces off its posterior end by muscular contractions. When kept in confinement it soon commences to constrict its body at various points, and after a few hours there is nothing left but a mass of fragments. It is viviparous, that is, it carries its young in the body-cavity; the eggs are hatched, and the young approach maturity before they are expelled. This species ranges from Cape Cod to North Carolina, and can be found in the upper part of its burrows when the tide is out.
S. roseola. This species occurs in the same localities as S. tenuis, and differs from it mainly in color, which is pale red, due to minute red spots scattered through the skin.
S. rotifera. A species found in Florida. It is light purplish in color, and has eight or ten branches on each of the twelve tentacles. In this species the spicules of lime in the skin are shaped like wheels instead of anchors.
Genus Caudina