Chapter IX: Part II: Marine Invertebrates (4)

A curious organ found in the /Echinoidea/ (sea-urchins) is called /Aristotle's lantern/. It is a complicated arrangement, not fully understood, having forty parts, and is connected with the alimentary system. One of the parts is the mouth, over which five teeth project. These teeth grasp and grind the food. The exoskeleton is composed of plates of carbonate of lime, called /ossicles/, which cover the surface of the body. The ossicles are of various sizes and shapes, and are one of the determining features in classification. They may be scattered spicules of lime, separated plates joined by connecting rods, or overlapping plates; or they may be fitted together so as to form a continuous shell. The starfishes are usually carnivorous, the sea-urchins usually vegetarian, while the holothurians, after the manner of worms, take in sand and mud, deriving their nourishment from the organic particles contained in them. All echinoderms live in the sea. [pg204]

TABLE SHOWING THE CLASSIFICATION OF THE STARFISHES DESCRIBED IN THIS CHAPTER.

Class =ASTEROIDEA= (/Starfishes/)

Order =PHANEROZONIA= (/Ossicles not crowded; large marginal
ossicles; spines only on dorsal surface; pedicellariae sessile/)

Families Genera Species

~PORCELLANASTERIDAE~ ^Ctenodiscus^ ^C. corniculatus^

~ASTROPECTINIDAE~ ^Astropecten^ ^A. articularis^
^Psilaster^ ^P. florae^
^Luidia^ ^L. senegalensis^
^L. clathrata^
^L. alternata^

~PENTAGONASTERIDAE~ ^Mediaster^ ^M. aequalis^

~ANTHENEIDAE~ ^Hippasteria^ ^H. phrygiana^

~PENTACEROTIDAE~ ^Pentaceros^ ^P. occidentalis^
^P. reticularis^
^Nidorella^ ^N. armata^

~ASTERINIDAE~ ^Asterina^ ^A. folium^
^A. miniata^

Order =CRYPTOZONIA= (/Ossicles crowded; pedicellariae stalked/)

~SOLASTERIDAE~ ^Solaster^ ^S. endeca^
^S. decemradiata^
^Crossaster^ ^C. papposus^

~ECHINASTERIDAE~ ^Cribrella^ ^C. sanguinolenta^
^Echinaster^ ^E. sentus^

~HELIASTERIDAE~ ^Heliaster^ ^H. multiradiata^

~ASTERIIDAE~ ^Asterias^ ^A. vulgaris^
^A. Forbesii^
^A. ochracea^
^A. gigantea^

[pg205]

CLASS =ASTEROIDEA=

THE STARFISHES

These animals are named from their star-shaped outline. Some have five long, spreading arms diverging from a small disk, which is hardly more than their point of union; others have a large body with short arms, which are like angular projections of the body, giving a pentagonal shape. Some genera have a greater number of arms than others; /Solaster/ has eleven to thirteen, and /Heliaster/ (the sun-stars, found on the west tropical coast) has thirty to forty.

The mouth of the starfish is in the center of the ventral side. A ventral or /ambulacral groove/ extends through each arm. In these grooves the ambulacra, or tube-feet, are arranged in rows. The /ambulacra/ are hollow, cylindrical bodies, each of which has a sucker at one end, and is connected at the other end with a little globular body, the /ampulla/. The ventral groove forms a ridge in the body-cavity. It is called the /ambulacral zone/, and is formed by a double row of elongated plates, which meet and form a raised line along the middle of the inside of the arms, and appear like ribs; between them lie the ampullae. These plates are called the /ambulacral ossicles/. Numerous other ossicles extend over the surface, buried in the integument of the body, making a calcareous network, or /exoskeleton/. The ossicles are connected by muscles so that the animal is not rigid, but is able to bend the body and even creep through comparatively small places. The ossicles are covered with /spines/ of two kinds. The very minute ones are the /pedicellariae/, and have a jointed end which opens and shuts like a pincers. Their principal use seems to be to remove waste matter or other substances from the body, keeping it free and clean. The pedicellariae are arranged, in some species, in circles around the [pg206] bases of the spines, and form groups over the dorsal surface. Examining the backs of different starfishes with a strong magnifying-glass, one will be surprised to see the varied grouping of the spines and pedicellariae. At the extremity of each arm is a red eye-spot, which is sensitive to light, and a tube-foot, which has no sucker and which is believed to act both as an olfactory and as a feeling organ. The madreporic plate lies at the angle of two of the arms or rays. Water filters through the madreporic plate and passes by the stone-canal to the ring-canal around the mouth, and thence to the radial tubes, one of which extends through each arm and is connected by a branch with each tube-foot. At the base of each tube-foot there is a globular reservoir, or ampulla. A valve connects the tube-foot and ampulla. When the ampulla is contracted, water is forced into and distends the tube-foot; when the ampulla is distended, it withdraws the water from the tube-foot, thus acting like a suction-bulb. When water is sent into the tube-feet they are greatly extended and are then placed against an object. The water being then withdrawn through the ampullae, a vacuum is formed, and the suckers are tightly attached. By the alternating movements of the ambulacra the animal is dragged slowly along and moves with a gliding motion. It does not deviate from a straight path, going over elevations or through depressions without turning aside; its body conforms to the irregularities of the road and never bridges over spaces. The stomach extends a little way into the arms, and a short intestine leads to the excretory opening in the center of the back. Starfishes are carnivorous and voracious, and are particularly [pg207] destructive to oyster-beds. The animal fastens itself to a bivalve, and protrudes a part of its stomach, with which it envelops its prey and slowly sucks it out of its shell. When feeding on small mollusks they take them into the stomach directly. Starfishes regain by natural growth parts of the body which may be lost. Sometimes the animal throws off an arm to escape capture, and self-mutilation also occurs where unfavorable conditions exist. Oystermen formerly were ignorant of the starfish's wonderful powers of regeneration, and were in the habit of cutting up those captured in their forks and throwing them overboard, thus increasing the number instead of destroying their enemies, as each arm with a piece of the body attached to it will, it is said, become a new individual. This tenacity of life makes starfishes difficult to destroy, and they are exceedingly plentiful in all seas. One naturalist speaks of seeing on the coast of Maine a bed of starfishes which extended several miles and covered the bottom so closely that he picked sixty individuals off a small stone. On the northern shores of the Pacific coast they abound in great variety, and some are of unusual size. /Asterias gigantea/ of this region measures two feet across. Another species, /Phyncopodia helianthoides/, measures a yard in diameter, and has twenty or more arms. The most common species of the Atlantic coast are /Asterias vulgaris/ and /A. Forbesii/; the former ranges from Long Island northward, the latter from Massachusetts to Florida. These are the species particularly destructive to oyster-beds. /Asterias vulgaris/ sometimes grows to be fifteen inches in diameter; from this, which is perhaps the largest, are found starfishes of all sizes down to the very small /Cribrella/. They inhabit all varieties of bottoms, from low-water mark to deep water. They are not always abundant in the same place, but seem to move about.

Some oystermen believe that the starfishes get into masses like a ball and are rolled along by the tide. This idea comes from the fact that an oyster-bed may be free from them one day and the next be covered by these pests. To get rid of them the beds are swept over with a tangle, which is an iron bar holding swabs of raveled rope. The spines of the starfish are caught in the [pg208] tangle, and often hundreds are brought up in one haul and are then killed by steaming.

The anatomical system of the starfish is easily traced by cutting off, with scissors, the skin from the dorsal surface of the disk, and also cutting a slit down one of the arms. In the center of the body will be seen the upper part of the stomach, a small star-like spot, from which radiate five branches, which divide and lead into the much-ramified, plume-like organs which extend through the arms. These are the pyloric caeca, whose function is to secrete the digestive fluids. The much-folded stomach occupies the greater part of the central space, its large convolutions showing on top. The mouth connects with the stomach on the ventral side. By turning back the skin from the arm, small filiform processes can in some large species be seen; these are the dermal branchiae, or breathing-organs, which may either project through pores in the skin between the ossicles or be entirely retracted. If the pyloric caeca be laid back, one can see the rib-like arrangement of the ambulacral ossicles, and also the ampullae, which lie between the ossicles on each side of the ridge. If an ampulla be inflated and then pressed, the corresponding tube-foot will be seen to extend. To follow successfully the water-vascular system, beginning in the madreporic plate and extending through the stone-canal to the ring-canal around the mouth and thence through the arms, requires a strong glass and more skilful manipulation.

ORDER =PHANEROZONIA=

FAMILY ~PORCELLANASTERIDAE~

GENUS ^Ctenodiscus^ (Plate LII.)

^C. corniculatus.^ Pentagonal; about two and a half inches in
diameter; the body flat, with wide marginal plates, giving a
flat edge to the rather long, pointed arms; madreporic plate
large; color greenish; ambulacra without suckers, seeming to be
adapted to pushing through soft mud rather than dragging over hard
surfaces. It lives in deep water on muddy bottoms and ranges from
Massachusetts to Greenland. When dredged the animal is usually
found to be filled with soft mud.

FAMILY ~ASTROPECTINIDAE~

In this family there are only two rows of tube-feet; the rays end in sharp points and have large ossicles on the margins. [pg209]

GENUS ^Astropecten^

^A. articularis.^ The body is flat and smooth; the rays sharply
pointed and conspicuously bordered with marginal ossicles and
fringed with short spines; two rows of ambulacral feet; color rich
purple. Found in shallow waters of South Atlantic coast on sandy
bottoms. (Plate LII.)

GENUS ^Psilaster^

^P. florae.^ Diameter four to five inches; arms sharply pointed
and conspicuously bordered with large ossicles; body flat, with
smooth surface, the ossicles seeming like mosaic; bright pinkish
flesh-color. It occurs in deep water off the eastern coast as far
south as New Jersey.

GENUS ^Luidia^

This genus of starfishes is celebrated for its peculiar habit of breaking in pieces when taken from the water, and therefore good specimens are almost impossible to obtain.

^L. senegalensis.^ Twelve to fourteen inches across; arms long and
narrow, tapering to a point and fringed on the edges with spines;
surface rather smooth, showing the separation of the ossicles;
color almost white, with dark line running through the center of
each arm; usually nine arms. Found in shallow water on the coasts
of Florida and the Gulf of Mexico.

^L. clathrata.^ Four to five inches across; light-colored; with
a fringe of spines on the margins of the arms, which taper to
a point; two rows of ambulacra. It is found from New Jersey
southward, and is one of the most common starfishes on the sandy
beaches of North and South Carolina. (Plate LII.)

^L. alternata.^ Upper surface purplish, with irregular yellowish
bands on the arms; under surface yellow. Found in shallow water on
the Florida coast.

FAMILY ~PENTAGONASTERIDAE~

GENUS ^Mediaster^

^M. aequalis.^ Body flat; the five rays equal or exceed in length
the diameter of the disk; margins have double row of large plates;
surface covered with granules, which are easily rubbed off; bright
red above, pale orange below; diameter four inches. Common on the
coasts of Oregon and California.

FAMILY ~ANTHENEIDAE~

GENUS ^Hippasteria^

^H. phrygiana.^ This beautiful starfish lives in deep water, but
is sometimes thrown up on the beach, and ranges from Cape Cod
northward. [pg210] It has a large, pentagonal, bright-scarlet
disk, five to six inches in diameter, with arms rather long and
pointed. The upper side is raised and cushion-like, and is covered
with blunt spines; the margins have larger spines of the same
shape. The pedicellariae are sessile and so long and large as to be
easily seen with the naked eye. (Plate LII.)

FAMILY ~PENTACEROTIDAE~

GENUS ^Pentaceros^

^P. occidentalis.^ Pentagonal; eight to twelve inches in diameter;
ossicles a network of rod-like plates, with prominent spines at
the points of union; body inflated in the center and running in
wedge-like form to the ends of the rather long and narrow arms; the
upper lines of the ridges have spines more prominent than those
on the rest of the body; the spines of the larger specimens are
more like large warts or small hemispheres. Found on the Lower
California coast.

^P. reticularis.^ This starfish is the largest species on our
coasts. It is common in southern Florida close to the shore. The
body is three to four inches thick, flat on the oral surface, but
raised on the upper side, and tapers down in wedge-like form to the
points of the short arms. The prominent blunt spines which cover
its surface are arranged in a somewhat regular net-like order, and
the sharp-edged margins have an even row of larger spines of the
same form. The madreporic plate is nearly in the center of the
disk, and is quite conspicuous, being bordered with a circle of
small spines. Its color is dull yellow, and its size often a foot
or more in diameter. It is the large starfish so often seen in
curiosity-shops. (Plate LII.)

GENUS ^Nidorella^

^N. armata.^ This very curious pentagonal species, found on the
California coast, is five to six inches in diameter and red in
color. The upper surface is raised and covered with thick, pointed
spines one half of an inch to one inch long, arranged in lines, but
not crowded. The ossicles on the margins are large; some of them
are hemispherical and bear large spines. Smaller spines border the
under edge of the margins. (Plate LIII.)

FAMILY ~ASTERINIDAE~

The starfishes of this family are pentagonal, with a large body and short arms. The disk is more or less elevated in the center, and the edges are sharp. There are two rows of ambulacra. The ossicles are notched and overlapping. The family is confined to temperate and tropical waters.

GENUS ^Asterina^

^A. folium.^ Small, pentagonal, swollen (gibbous). Found on the
Florida coast.

^A. miniata.^ Pentagonal; somewhat raised in center; about one and
a half inches across; edges sharp. Found on the California coast
close to shore. (Plate LIII.)

ORDER =CRYPTOZONIA=

FAMILY ~SOLASTERIDAE~

GENUS ^Solaster^

^S. endeca.^ Dark red in color; nine to eleven arms, which are
shorter than the breadth of the disk; diameter of disk about five
inches; two rows of ambulacra; surface rather smooth. Common on
the coast of Maine, and found from Cape Cod to Newfoundland below
low-water mark.

^S. decemradiata.^ This species is common on the North Pacific
coast. It has ten arms, which are about twice the length of the
diameter of the body, the whole body being about a foot across.
(Plate LIII.)

GENUS ^Crossaster^

^C. papposus.^ Twelve to fifteen arms, half as long as the breadth
of the body; upper surface an open network of calcareous rods,
or ossicles; at their points of union are club-shaped tubercles
bearing tufts of smaller spines; concentric lines and spots of red
and purple over the spiny upper surface; color light underneath.
Common on the New England coast. (Plate LIII.)

FAMILY ~ECHINASTERIDAE~

GENUS ^Cribrella^

^C. sanguinolenta.^ This species is abundant north of Cape Cod and
is found of all sizes from half an inch to two inches in diameter
and of various colors--purple, orange, red, yellow, flesh-color,
etc. It has five round arms, generally about four times as long as
the breadth of the disk. The ends are often turned upward. It is
covered with crowded short spines, like little warts, which give
it a nearly smooth surface. It has two rows of ambulacra. It moves
with two of its arms turned forward, as if they were dragging the
other three behind them. Unlike most species, the young are not
free-swimming, but the eggs are carried around the mouth of the
mother, and the young are retained there until they are capable of
taking care or themselves. (Plate LIV.)

GENUS ^Echinaster^

^E. sentus.^ This species occurs close to shore in the waters of
Florida and is perhaps the most commonly observed species on the
beach. It extends as far north as New Jersey. It is purplish in
color, and about four and a half inches in diameter, with two rows
of ambulacra, five arms, and a surface rough with spines. [pg212]

FAMILY ~HELIASTERIDAE~

GENUS ^Heliaster^

^H. multiradiata.^ Spines on the upper surface of rays in five
rows, but close to the disk proper become reduced to one row. Found
on the coasts of Lower California and Mexico. (Plate LIV.)

FAMILY ~ASTERIIDAE~

The /Asteriidae/ have the following characteristics: four rows of tube-feet; ossicles small and unequal; spines isolated or grouped; pedicellariae of two forms, forceps-like and scissors-like respectively. They include the very common forms found on all beaches.

GENUS ^Asterias^

^A. vulgaris.^ The common starfish of the Atlantic coast, from
Long Island Sound to Labrador. It occurs at low-water mark and
extends into deep water. It has five arms, which taper to a point.
Large specimens measure fifteen inches across. The upper surface
is rough, being covered with short spines, which are largest and
thickest at the edges of the rays, and surrounding them are the
pedicellariae. The color varies from pink, yellow, and brown to
purple.

^A. Forbesii.^ The common starfish of the Atlantic coast, from
Massachusetts Bay to the Gulf of Mexico. This species resembles
very closely /A. vulgaris/, but can be distinguished from it by
the madreporic plate, which is bright orange, while in the former
it has the same color as the animal; also the arms are a little
swollen at the base and terminate more bluntly. These two species
are very destructive to oyster-beds, especially where their ranges
overlap. It is computed that they destroy annually two hundred
thousand dollars' worth of oysters. Vast numbers congregate where
the feeding-ground is good, and move in long lines from place
to place. The oystermen dredge over the beds and bring them up
in thousands, then steam them or throw them on the shore above
high-water mark. (Plate LIV.)

^A. ochracea.^ The common starfish of the Pacific coast, from
Sitka to San Diego. Five rays, each hardly twice as long as the
diameter of the body; spines running irregularly over the surface,
but forming a pentagon at the middle of the disk and inclosing the
madreporic plate; diameter eight inches. It is very common near San
Francisco on rocks at low-water mark. (Plate LIV.)

^A. gigantea.^ Body very large and swollen; six rays, somewhat
less in length than twice the diameter of the disk; aboral surface
covered with numerous short, blunt, equidistant spines of uniform
size and regularly distributed; spines contracted at the base and
striated; diameter two feet. Found on the California coast.

TABLE SHOWING THE CLASSIFICATION OF THE BRITTLE-STARS DESCRIBED IN THIS CHAPTER.

Class =OPHIUROIDEA= (/Brittle-stars/)

Order =EURYALIDA= (/Skin without plates; arms simple or branched,
and capable of being rolled up/)

Genera Species

^Astrophyton^ ^A. Agassizii^

Order =OPHIURIDA= (/Skin with plates/)

^Ophiopholis^ ^O. aculeata^
^Amphiura^ ^A. squamata^
^Ophiocoma^ ^O. riisei^
^O. aethiops^
^O. Alexandri^
^Ophiothrix^ ^O. angulata^

[pg214]

CLASS =OPHIUROIDEA=

BRITTLE-STARS

The ophiurans, or brittle-stars, differ from the starfishes in having the arms quite distinct from the body. In starfishes the arms are extensions of the body, and the viscera extend partway into them, while in ophiurans the body is a central disk, with the five narrow arms attached to its margin. In form they suggest a spider, and sometimes are called sea-spiders. The name brittle-star is also descriptive, since they break off their limbs readily. The arms are narrow, taper to a point, usually curl at the ends, and have no ambulacral grooves, but are completely covered with bare calcareous plates (except in the first order, where they have a skin and no plates). The ambulacra are small spines without suckers, which emanate from the sides or margins of the arms and do not serve for walking. The madreporic plate is on the ventral surface, in one of the circular shields which surround the mouth. The alimentary canal ends blindly. The egg-sacs lie between the arms and open by slits on the under side, close to the arms, where they join the disk. Water flows in and out of these pouches, which are thought to have also respiratory and excretory functions. No eye-specks have been found, but they must exist, since the animal is sensible to approaching danger and quickly retreats. The ophiurans are more active than starfishes, moving by wriggling, and clambering with their arms. They are shy and hard to find, and it is difficult to capture a whole one, since they throw off pieces of their arms at the least alarm. Often they completely dismember themselves, an action which does them no permanent injury, since they reproduce lost parts. They are more commonly inhabitants of deep than of shallow waters, and are brought up from the bottom in dredges in great numbers. [pg215] Some species may be found near low-water mark under stones and in clusters of mussels, and often in seaweeds, thrown up from deep water, on the shore.

ORDER =EURYALIDA=

GENUS ^Astrophyton^ (Plate LV.)

^A. Agassizii.^ This very singular ophiuran is commonly called the
basket-fish, from its resemblance to a basket when the tentacles
are rolled up. Its body is covered with skin instead of calcareous
plates. The body is thick and somewhat circular in form, with
elevated radiating ridges on the upper side, and the skin is marked
off in star-like divisions. From the margin of the body extend
five arms, which at once divide in a forking manner; each section
again divides, and this division in pairs (dichotomous division)
continues until the ends of the arms have become very numerous and
attenuated. The arms are carried curled up or straight at will. In
moving, the animal seems to walk on these branches as if on tiptoe,
and in this position it forms a kind of net which entraps prey. The
arms and prominent parts of the disk are yellow, and the depressed
or membranous parts brown. /Astrophyton/ is six to eighteen inches
in diameter. It is found off the northern New England coast.

ORDER =OPHIURIDA=

GENUS ^Ophiopholis^

^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. aethiops^, ^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.)

[pg217]

TABLE SHOWING THE CLASSIFICATION OF THE ECHINOIDEA DESCRIBED IN THIS CHAPTER

=Class= =ECHINOIDEA=

Order =DESMOSTICHA= or =REGULARIA= (/Shell usually globular; mouth
and anus polar; lantern of Aristotle present/)

Families Genera Species

~CIDARIDAE~ ^Cidaris^ ^C. tribuloides^
^Dorocidaris^ ^D. papillota^
^D. Blakei^
^Porocidaris^ ^P. sharreri^

~ARBACIADAE~ ^Arbacia^ ^A. punctulata^
^C[oe]lopleurus^ ^C. floridanus^

~DIADEMATIDAE~ ^Diadema^ ^D. setosum^

~ECHINOMETRIDAE~ ^Echinometra^ ^E. subangularis^

^Strongylocentrotus^ ^S. drobachiensis^
^S. purpuratus^
^S. franciscanus^

~ECHINIDAE~ ^Echinus^ ^E. gracilis^
^Toxopneustes^ ^T. variegatus^

Order =CLYPEASTROIDEA= (/Corona or shell a more or less flattened
disk; anus excentric; lantern of Aristotle present/)

~ECHINANTHIDAE~ ^Clypeaster^ ^C. ravenellii^
^Echinanthus^ ^E. rosaceus^

~SCUTELLIDAE~ ^Echinarachnius^ ^E. parma^
^E. excentricus^
^Mellita^ ^M. testudinata^
^Encope^ ^E. michelini^

Order =SPATANGOIDEA= or =PETALOSTICHA= (/Heart-shaped; mouth and
excretory opening excentric; no lantern of Aristotle/)

~SPATANGOIDAE~ ^Moira^ ^M. atropos^
^Lovenia^ ^L. cordiformis^
^Schizaster^ ^S. fragilis^
^Metalia^ ^M. pectoralis^
^Brissopsis^ ^B. lyrifera^

[pg218]

CLASS =ECHINOIDEA=

SEA-URCHINS, CAKE-URCHINS, HEART-URCHINS

ORDER =DESMOSTICHA=

SEA-URCHINS

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 /ampullae/ (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 /pedicellariae/, 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 pedicellariae 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 /sphaeridia/, 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 larvae, 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]

FAMILY ~CIDARIDAE~

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.)

FAMILY ~ARBACIADAE~

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 ^C[oe]lopleurus^

^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.

FAMILY ~DIADEMATIDAE~

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.)

FAMILY ~ECHINOMETRIDAE~

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 algae, 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 pedicellariae
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.)

FAMILY ~ECHINIDAE~

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.

ORDER =CLYPEASTROIDEA=

CAKE-URCHINS

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.

FAMILY ~ECHINANTHIDAE~

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.

FAMILY ~SCUTELLIDAE~

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.)

ORDER =SPATANGOIDEA=

HEART-URCHINS

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.

FAMILY ~SPATANGOIDAE~

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.

[pg227]

GENUS ^Lovenia^

^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]

TABLE SHOWING THE CLASSIFICATION OF THE HOLOTHUROIDEA DESCRIBED IN THIS CHAPTER

Class =HOLOTHUROIDEA=

Order =ELASIPODA= (/Deep-sea forms; tube-feet in zones near
together/)

Order =PEDATA= (/Well-developed tube-feet and false ambulacra/)

Genera Species

^Thyone^ ^T. briareus^
^Pentacta^ ^P. frondosa^
^Lophothuria^ ^L. fabricii^

Order =APODA= (/Without radial canals, tube-feet, or respiratory
trees/)

^Synapta^ ^S. tenuis^
^S. roseola^
^S. rotifera^
^Caudina^ ^C. arenata^

[pg229]

CLASS =HOLOTHUROIDEA=

SEA-CUCUMBERS

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 larvae, 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 laevigata/ 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.

ORDER =PEDATA=

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 papillae. [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^ (Dueben), ^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.

ORDER =APODA=

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^

^C. arenata.^ About four inches long and tapers to the ends; the
posterior end sometimes narrowed to a long, slender, tail-like
extremity; tentacles around the mouth resemble cloves. It lives in
sand and may be found on the New England coast, washed ashore after
a storm. [pg234]

Class =CRINOIDEA=

Genera ^Pentacrinus^ ^Comatula^

CLASS =CRINOIDEA=

FEATHER-STARS AND SEA-LILIES