Chapter VIII: Part II: Marine Invertebrates (3)

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 algae.

PHYLUM =NEMATHELMINTHES=

ROUNDWORMS

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.

CLASS =NEMATODA=

GENUS ^Pontonema^

^P. marinum.^ Slender, white, smooth, active, cylindrical;
constantly coiling and uncoiling itself.

PHYLUM =ANNULATA=

SEGMENTED WORMS

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.

CLASS =CHAETOPODA=

("/Bristle-footed/")

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 /Aphroditidae/.

The body-cavity in chaetopod 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 chaetopod 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.

SUBCLASS =POLYCHAETA=

("/Many-bristled/")

The polychaete 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 /chaetae/. 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 chaetae, 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 polychaete 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 polychaetes form tubes (/Eunicidae/), and some /Sedentaria/ form no tubes.

Many polychaetes are beautifully colored, some in vivid reds and greens, with various markings; some are iridescent; some are phosphorescent.

ORDER =ERRANTIA=

Carnivorous, free /Polychaeta/, with protrusible pharynx armed with a horny jaw. "They are active, fierce beasts of prey."

FAMILY ~SYLLIDAE~

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 ~APHRODITIDAE~

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 ^Polynoe^

The species of /Polynoe/ 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 papillae 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 /Polynoe/
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 ^Harmothoe^

^H. imbricata.^ Sixteen pairs of smooth scales; variable in color;
usually gray, speckled, or striped.

GENUS ^Aphrodite^

^A. aculeata.^ This polychaete, sometimes called the sea-mouse, is
one of the most beautiful of worms. It is brightly iridescent in
color, from its setae, which form a fur-like coating over the dorsal
surface. It has fifteen pairs of scales, but they are hidden by
the numerous setae. 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 ~PHYLLODOCIDAE~

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 ~NEREIDAE~

GENUS ^Nereis^

Among the most common of the polychaete 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.

^N. virens.^ This species is found from New York northward in
muddy and shelly sand, and under rocks between tide-marks, living
in burrows, which it lines with a mucous secretion. It is very
active, and voracious, feeding on other worms, /Crustacea/, etc.,
which it captures with its horny, protruded jaw. At night it
leaves its burrow and swims freely about like an eel, frequently
falling a prey to fishes. In color it is dull bluish-green, with
some iridescence. The gills, which are leaf-like appendages on the
parapodia, are green on the anterior end of the body and become
bright red farther back. This species, and /N. branti/ of Alaska,
are the giants of polychaete worms, often measuring eighteen inches
or more in length.

^N. pelagica.^ Found in abundance on the New England shore and
northern coasts under stones and on shelly bottoms. The female is
four to five inches long, while the male is only two inches in
length. In this species the body is widest in the middle, while in
other species it is widest at the anterior end. The palps are long,
and the second head-piece (peristomium) is twice as long as the
next segment. The color is reddish-brown and iridescent.

^N. limbata.^ Five to six inches long; jaws light yellow, sharp,
and slender; parapodia and bristles smaller on the anterior than on
the posterior end; color dark brown, with light lines on the sides
and appendages, pale red on the posterior end; dorsal blood-vessel
apparent, and the heart-like pulsations can be distinctly seen.
The male worm is red in the middle section. Found along the middle
Atlantic coast on sandy shores.

FAMILY ~NEPHTHYDIDAE~

In this family the worms have a long, thick, flattish body, a section of which has a quadrangular form. The lobes of the parapodia are widely separated and fringed [pg178] with membrane, appearing like double parapodia. The pharynx is very large and projected as in /Nereis/.

GENUS ^Nephthys^

^N. ingens.^ Sometimes six inches long and one quarter of an inch
broad; usually smaller; color whitish, with red blood-vessel
showing on dorsal side; appendages dark blown; moves actively
and burrows quickly into the mud; when captured often breaks off
a portion of the posterior end, which it is able to reproduce;
proboscis large; branchiae between the dorsal and ventral parapodia.
Found burrowing in all kinds of mud on the New England coast.

^N. picta.^ More slender than /N. ingens/; color whitish, mottled
with brown on the dorsal anterior end; often a dark line down the
back; head square in front and triangular in the back. Found in
sandy mud at low-water mark.

FAMILY ~EUNICIDAE~

These are beautiful worms, having a reddish-brown iridescent body, with bright-red branching gills, which look like feathers, along the back. They form parchment-like tubes.

GENUS ^Marphysa^

^M. sanguinea.^ Length six inches or more; color bronze or
brownish-red and iridescent; has bright-red branched gills and six
caudal cirri of different lengths; body flattened, except at the
anterior end, where it becomes narrow and cylindrical; has powerful
jaws. It is found under stones and in clefts of rocks at low-water
mark, or more commonly in parchment-like tubes on shelly beaches,
from Cape Cod to New Jersey.

GENUS ^Diopatra^

^D. cuprea.^ This is one of the largest and most beautiful
annelids. It is found from Cape Cod to South Carolina at low-water
mark, in sandy mud-flats, living in long tubes which project above
the surface two or three inches and are hung with seaweeds and bits
of foreign matter. /Diopatra/ is twelve inches or more in length
and one half of an inch in breadth. In color it is reddish-brown,
specked with gray, and has a brilliant whitish or opal-like
iridescence. The appendages are yellowish-brown, specked with
green. The body is flattened. From the fifth segment long, dull
to bright red, much-branched gills, resembling plumes, [pg179]
extend nearly to the end of the worm. On the ventral side of the
parapodia are whitish tubercles with a dark spot in the middle.
These papillae secrete the long, broad tube in which the worm lives.
The worm is difficult to capture, for when pursued it retreats
quickly into its tube, which is so large that it can easily turn
around within it. (Plate XLVIII.)

GENUS ^Arabella^

^A. opalina.^ Body cylindrical, twelve to eighteen inches long,
one quarter of an inch wide in the middle, and tapers to the ends,
which are comparatively small; lateral appendages short; color
bronze, with brilliant, opal-like iridescence; head small, conical,
but blunt and without tentacles; four eyes in transverse row at the
base of the head; segments well marked; coils into spirals when
outside of its burrow. Found in compact sandy mud at low-water mark
on the New England coast.

GENUS ^Lumbriconereis^

^L. tenuis.^ Twelve inches or more long, and slender, like a fine
cord; bright red and somewhat iridescent; very fragile. Abundant
in sandy mud on the northern New England coast, and found from New
Jersey northward.

FAMILY ~GLYCERIDAE~

These worms are long and smooth, with numerous segments. They taper at both ends. The head is small, conical, sharply pointed, and has four very small tentacles. The proboscis, or [pg180] pharynx, when protruded, is very large and long, and appears too large for the worm. The proboscis has four hook-like jaws. These worms burrow rapidly and disappear almost instantly into the mud or sand.

GENUS ^Glycera^

^G. americana.^ Color red or purple; has branched gills on upper
side of parapodia. Found from South Carolina to Cape Cod on sandy
and muddy shores and flats near low-water mark.

^G. dibranchiata.^ Has a simple gill on both sides of the
parapodia; about eight inches long and one quarter of an inch wide
in the middle; proboscis one inch long and wider than the body on
the upper end. Abundant from New Jersey to Cape Cod.

ORDER =SEDENTARIA=

THE TUBICOLOUS WORMS

Many of this order construct tubes in which they live permanently. Some species of both /Sedentaria/ and /Errantia/ have habits pertaining to the other. These worms are without a protrusible pharynx and without jaws. The body is usually divided into two or three sections by segments and appendages of different forms. They have hair-setae on a limited number of segments only, varying with the species; the remaining segments have /uncini/, or hooked comb-like rows of setae, which are very small, but often crowded in bunches. Uncini exist also on segments having hair-setae. Parapodia are often lacking on the posterior parts and are usually without cirri. The gills are usually confined to the anterior end and are sometimes represented by tentacles around the head. The different species have characteristic tubes, formed by mucus secreted by epidermal glands. Sometimes the mucus hardens, making a parchment-like tube; again it cements together grains of sand, or bits of shell, seaweeds, etc. Some species secrete [pg181] calcareous tubes; these are often found on rocks, in coral, and in the shells of mollusks. The anterior end of the body is more highly developed than the posterior end.

FAMILY ~SPIONIDAE~

GENUS ^Nerine^

^N. agilis.^ Two to three inches long; slender; somewhat flattened
at the anterior end; head conical and sharp; the two tentacles
about one half of an inch long; four eyes; color reddish-brown,
light green on the sides; gills red; tentacles greenish-white. It
burrows with extreme rapidity and lives on exposed beaches near
low-water mark.

^N. coniocephala.^ Two and a half inches long, one sixteenth of an
inch in diameter; head conical; body flattened on the dorsal side,
round on the ventral side; has two long tentacles turned backward
and a membrane on the gills of the anterior segments; gills red;
bristles long and numerous.

FAMILY ~CIRRATULIDAE~

Worms of this family have a cylindrical body, more or less attenuated at each end; segments similar throughout; many segments with long, filamentous cirri which act as gills; and a conical head. They live in burrows.

GENUS ^Cirratulus^

^C. grandis.^ Four to six inches long; head acute; segments
numerous, short, and distinct; color dull yellow, or orange,
to brown, often iridescent beneath; ventral surface somewhat
flattened. Numerous long, filamentous, red to orange-colored cirri
extend nearly the whole length of the body and act as gills. It is
common in sand and gravel at low-water mark from Cape Cod to New
Jersey. [pg182]

FAMILY ~TEREBELLIDAE~

The body is cylindrical and largest on the anterior end; there are one to three pairs of more or less branched gills on the anterior end, and the ventral surface of the anterior segments is thickened by glands which secrete mucus for tube-building. These gland-spaces are called /shields/.

GENUS ^Thelepsus^

^T. cincinnatus.^ Two to four inches long; pale red; marked like
lacework on the back; gills have numerous unbranched filaments
arising separately in two transverse rows; tubes thin, transparent,
flexible, and hung with foreign substances; attached along the
whole length.

GENUS ^Amphitrite^

^A. ornata.^ Twelve to fifteen inches long; flesh-color, reddish,
or brown; three pairs of red plume-like gills and numerous
flesh-colored tentacles around the anterior end; tentacles
constantly in motion and sometimes extended eight or ten inches;
tubes a quarter of an inch or more in diameter, and firm, being
composed of sand and mud. It is found under stones in mud, gravel,
and sand at low-water mark from Cape Cod to New Jersey, often
associated with /Cirratulus grandis/.

GENERA ^Polycirrus^, ^Chaetobranchus^

^P. eximius^, ^C. sanguineus^. These are two species of bright-red,
fragile worms, found under stones, in mud. They do not form
tubes. The first is a small worm, the second twelve to fifteen
inches long. Both have long, crowded tentacles extending in
every direction and distended as the blood flows into them. /C.
sanguineus/ has [pg183] tentacles sixteen inches in extent, and
branched gills on short pedicels on the back. They are common in
mud at low-water mark from Cape Cod to New Jersey.

FAMILY ~AMPHICTENIDAE~

GENUS ^Cistenides^

^C. Gouldii^ constructs conical free tubes of grains of sand in
a single layer; body short and a little curved; head obliquely
flattened; two broad groups of golden bristles turned upward on
each side of the anterior end; one to two inches long; color
light red or flesh-color, mottled with red or blue. This is a
common worm, and its horn-shaped tubes are so plentiful as to
attract attention on sandy shores. They will repay examination
with a glass, so beautifully are they built. The worm has
bunches of golden bristles arranged in two rows close to the
flattened anterior end, which make a kind of operculum to the
tube. This feature makes the species easy to identify. The worm
is transparent; the internal organs showing through give it the
various bright colors. It is found on sandy and muddy shores from
New Jersey northward.

FAMILY ~MALDANIDAE~

The tubes of these animals are formed of sand, a short portion projecting, and are very abundant in certain places. There is a horny plate on the upper surface of the head, and the skin on the sides of the head is raised in folds. There is a funnel-like process at the posterior extremity; gills are lacking. Some of the segments in the middle of the body are longer than the rest.

GENUS ^Clymenella^

^C. torquata.^ Body long, composed of twenty-two segments; the
fifth segment has a collar-like fold; the caudal extremity is
funnel-shaped and edged with papillae; both [pg184] the first and
the last three segments are bare, the rest have short bristles
above and hooks below; head has a prominent convex plate with a
raised border; worm pale red, with bright-red bands around the
segments, sometimes brownish. It constructs nearly straight tubes
of pure sand close to low-water mark in sheltered coves, and ranges
from New Jersey northward.

GENUS ^Maldane^

^M. elongata.^ Six to eight inches long, one eighth to one quarter
of an inch in diameter; body cylindrical, cut obliquely at both
ends; head bordered by a slight fold; color brown, with red blood
showing through. Found in sandy mud at low-water mark, in firm,
deep tubes of fine mud, on the New England coast.

FAMILY ~ARENICOLIDAE~

GENUS ^Arenicola^

^A. marina.^ Five to ten inches long; brownish-green; body
cylindrical, thickest on the anterior end; anterior and posterior
ends without chaetae; twelve to thirteen pairs of branched red gills
on the central segments. It makes burrows eighteen to twenty-four
inches deep on sandy southern shores, and can be traced by castings
at the mouth of the burrow. Commonly known as "lugworm," and used
by fishermen for bait.

FAMILY ~SABELLIDAE~

In this family the gills arise from two semicircular bases forming the crown; the second lobe of the anterior extremity is reversed like a collar; the gill-filaments have secondary processes, and the tubes are flexible, composed of cemented mud or sand. Found under stones, the tube passing around the stone and opening upward.

GENUS ^Sabella^

^S. microphthalma.^ Length of tube one and a quarter inches,
diameter one eighth of an inch; body olive-green, specked with
white; wreath of tentacles half as long as the body; tentacles pale
yellowish or flesh-colored, with transverse lines of darker color.
It is found on the southern New England coast.

FAMILY ~SERPULIDAE~

This family forms white calcareous tubes. One of the dorsal gill-filaments is flattened, forming an operculum, or cover, with [pg185] which the tube is closed when the worm has withdrawn itself inside. The tubes are commonly found attached to shells and rocks, usually solitary, but sometimes in clusters, crossing and recrossing each other on the surface of the shell or rock. Plume-like gills are attached to the anterior end of the body. The color differs in different species. These worms may easily be mistaken for the mollusks /Vermetus/, which live in similar tubes of larger size, growing in masses.

GENUS ^Serpula^

^S. dianthus.^ Tubes often three inches long and one eighth of
an inch wide, the fixed end coiled and contorted, free end with
circular opening; tubes often show circular ridges, marking periods
of growth; operculum funnel-shaped, the exterior striated and the
edge bordered with short processes; wreath of gills nearly circular
and divided into two symmetrical parts; color variable. It is found
in tide-pools, also on the under side of rocks at low-water mark,
either solitary or congregated in masses, and ranges from Cape Cod
to New Jersey.

GENUS ^Spirorbis^

^S. borealis.^ A minute calcareous tube, in a close, flat coil
attached on one side; easily mistaken for a minute gasteropod
shell; worm has an operculum and wreath of gills. Found on the
fronds of seaweeds, on shells, etc.

CLASS =GEPHYREA=

This class of animals, once placed near the holothurians, belongs with the annelid worms on account of their mode of development, their structure being entirely dissimilar. They are without segments and without parapodia. The body-cavity is filled with fluid and is traversed by connective tissue and fine muscular fibers. They are subcylindrical animals which can retract the anterior end of the body. The mouth is surrounded by tentacles, or by tentacular folds, and is at the base of the proboscis. They live in fissures of rocks, in sand, mud, rock, or coral, and in deep gasteropod shells. Their distribution is general.

ORDER =SIPUNCULOIDEA=

GENUS ^Sipunculus^

^S. nudus.^ The body is cylindrical, a foot or more in length
when extended. It is divided into two portions. The anterior end,
to the [pg186] extent of one sixth of the entire length of the
worm, is capable of being withdrawn into the remainder of the body.
This portion is called the /introvert/. The introvert is retracted
by means of special muscles forming a sheath around the gullet
and connected at the other end to the body-wall about half-way
down the body. It is narrower than the rest of the body and is
covered more or less closely with small horny papillae which turn
backward and overlap like scales. The rest of the body is divided
into longitudinal furrows and circular markings, giving it the
appearance of being divided into squares. These markings correspond
to muscles which lie beneath. The introvert, when retracted, leaves
at the opening a lobed and plaited fold of the integument, giving
the appearance of tentacles. When the introvert is expanded there
is a fringe-like funnel around the mouth. The body is covered with
a horny cuticle and has an iridescent luster. The animal lives
buried in the sand and feeds upon sand, deriving its nourishment
from the organisms contained therein. The sipunculoids pass so much
sand and mud through their bodies that they are said to modify the
mineral substances on the bottom of the sea, as earthworms do the
soil of the land.

GENUS ^Phascolosoma^

^P. Gouldii.^ Body cylindrical, a foot or more in length, a
quarter or half of an inch in diameter when expanded; but the
body constantly changes in size and shape as it is contracted or
expanded; surface of body parchment-like in texture and marked off
in small squares; color dull white to light brown. It is found on
the New England coast in sand and gravel at low-water mark.

IV

MOLLUSCOIDA

TABLE SHOWING THE CLASSIFICATION OF THE MOLLUSCOIDA DESCRIBED IN THIS CHAPTER

Class =POLYZOA=

Subclass =Ectoprocta= (/Excretory opening outside lophophore;
mouth in center of circle of tentacles; tentacles retractile/)

Order =GYMNOLAEMATA= (/Circular lophophore/)

Suborder ~CYCLOSTOMATA~ (/Tubular calcareous zo[oe]cia,
with circular apertures devoid of closing apparatus/)

Set ARTICULATA (/Erect branches divided at intervals by
chitinous joints/)

Genera Species

^Crisia^ ^C. eburnea^

Set INARTICULATA (/Erect or adherent zoarium; unjointed/)

^Tubulipora^ ^T. flabellaris^
^Diastopora^ ^D. patina^

Suborder ~CHEILOSTOMATA~ (/Calcareous or chitinous
zo[oe]cia, usually with opercula; avicularia, vibracula,
and ovicells often present/)

Set CELLULARINA (/Flexible erect forms/)

^AEtea^ ^AE. anguinea^
^Eucratea^ ^E. chelata^
^Cellularia^ ^C. ternata^
^Caberea^ ^C. Ellisii^
^Bugula^ ^B. turrita^
^B. Murrayana^
^B. flabellata^

Set FLUSTRINA (/Cells quadrate; front wall of zo[oe]cium
membranous or depressed, and has ridge-like margin/)

^Flustra^ ^F. membranacea^
^Membranipora^ ^M. pilosa^
^M. lineata^
^M. tenuis^

Set ESCHARINA (/Zo[oe]cium wholly calcified/)

^Escharella^ ^E. variabilis^
^Mollia^ ^M. hyalina^
^Cellepora^ ^C. scabra^
^C. ramulosa^
^C. pumicosa^

Suborder ~CTENOSTOMATA~ (/Horny or gelatinous zo[oe]cia,
having tooth-like processes which close the apertures when
the tentacles are retracted/)

^Alcyonidium^ ^A. ramosum^
^A. hirsutum^
^A. hispidum^
^A. parasiticum^
^Vesicularia^ ^V. dichotoma^
^V. custata^

Subclass =Entoprocta= (/Excretory opening within lophophore;
mouth near margin of area, which is surrounded by tentacles;
tentacles roll up instead of being retracted/)

^Pedicellina^ ^P. americana^

[pg190]

TERMS USED IN DESCRIBING POLYZOA

^Avicula'ria^: Specifically modified zo[oe]cia, resembling a bird's head, found only in the /Cheilostomata/.

^Brown bodies^: Brown pigment-masses contained in the zo[oe]cia and derived from the breaking down of the polypides.

^Lo'phophore^: The disk bearing the mouth and circlet of ciliated tentacles.

^Orifice^: The open end of the zo[oe]cium.

^Ovicell^: The receptacle in which the eggs develop.

^Pe'ristome^: The ridge around the orifice of cell.

^Po'lypide^: The parts of the animal within the zo[oe]cium.

^Vibra'cula^: A lashing filament, or specifically modified zo[oe]cia, found only in the /Cheilostomata/.

^Zoa'rium^: The whole colony.

^Zo[oe]'cium^: The body-wall of a single individual. [pg191]

POLYZOA

Among the numerous objects to be found on the beach at low tide are the /Polyzoa/, of which there are said to be seventeen hundred named species of the marine forms. These little animals, although so plentiful, are inconspicuous, and it may be said that their very existence is not known to those who are not professed naturalists; yet they are easy to see, incrusting with a delicate calcareous lacework the surface of stones and shells and seaweeds in the tide-pools, and hanging from the rocks like branches of delicate seaweeds. There is hardly a frond of even the fine red algae on which cannot be found the little tube holding shelly saucers, or the creeping stems or branches of polyzoans. Any one of these little masses, when examined with a pocket-glass, will surprise one with its delicate and beautiful structure.

This class of animals is also called /Bryozoa/, and certain species have the common names of sea-mats and corallines. They are broadly divided into two groups, namely, the erect and the incrusting forms. Those having tree- or plant-like shapes resemble seaweeds, while the colonies which spread over stones, shells, and algae resemble moss, hence the name /Bryozoa/ (moss-animals). Both groups have the general appearance of hydroids, because, like them, they are colonies having plant forms and having their organisms inclosed in cup-like sheaths. The resemblance, however, is but a superficial one, for the /Polyzoa/ have a much higher organization, each animal of the colony being a separate and distinct individual. They can easily be distinguished by the hair-like processes on the tentacles. The ciliated tentacles and complete alimentary system are the conspicuous differences between these colonies and those of the hydroids.

The /Polyzoa/ are very numerous and form a most attractive [pg192] group. They are plentiful everywhere, occurring between tide-marks and at great depths on the floor of the sea. Rocks protected from the sun are often incrusted with the calcareous forms, while branching species hang from the rocks and adorn rock pools. /Membranipora/, in lace-like sheets, will be found on the larger seaweeds as well as on various submerged objects. The beautiful little /Crisia/ may be looked for on the fronds of red algae, and /Alcyonidium/, in soft moss-like patches, on /Fucus/. On some beaches are scattered the sea-mats, /Flustra foliacea/, looking like bits of brown paper. A pocket-lens will reveal the marvelous and orderly arrangement of the two layers of cells, or zo[oe]cia, placed back to back. There is not a more surprising object in the animal kingdom than a living branch of /Bugula/. The cells on its spiral, profusely branched clusters have appendages resembling a bird's head, with its bill constantly opening and shutting. Of the erect polyzoans some are entirely calcareous and rigid; such species live in deep water, and their colonies are called corallines, as are also the calcareous algae. They have existed in vast numbers since early geologic times, and are plentiful in the Tertiary deposits, known as Coralline Crags. Other erect forms have a calcareous framework, which is not continuous, but has horny intervals, so that the colonies are flexible and can be swayed by the tides in shallow water where they live. Others have complete horny exoskeletons. The same differences occur in the incrusting forms, those on the seaweeds being either flexible, so that they bend with the plant, or if entirely calcareous are so small that they do not break when the plant sways to and fro. Still others are gelatinous and resemble bits of sponge. The calcareous forms are usually ornamented with ridges which form beautiful patterns.

The individuals of the polyzoan colonies are small polyp-like organisms which have a cup-like inclosure of horny or of calcareous substance, or of the two combined, as mentioned above. This inclosing sheath is the exterior or cuticle of the animal and is called the /zo[oe]cium/, the whole colony being called the /zoarium/. The animal substance within the zo[oe]cium is the /polypide/, and consists of the mouth, tentacles, and alimentary system. A disk at the anterior end of the body, bearing the circle of tentacles, is [pg193] the /lophophore/; it is a contractile body, being, with the tentacles, protruded from the zo[oe]cium or drawn within it at will. In some species the orifices of the zo[oe]cia are surrounded with spines; others have lids, called /opercula/, which shut down when the polypides are retracted. A singular modification of the zo[oe]cia is seen in the genus /Bugula/, where peculiar shapes like birds' heads, called /avicularia/, occur. In these singular appendages the upper beak is hooked, while the lower one, or mandible, is the operculum of the zo[oe]cium. These constantly open and shut by means of muscles, and although their function is not certainly known, it is thought that they capture prey. Other modifications are whip-like processes, or flagellate filaments, called /vibracula/, which constantly beat the water. In many of the zo[oe]cia of the colony there are dark-colored masses, called /brown bodies/. These are formed by the degeneration of the polypides, which at certain periods break down, their tentacles and alimentary system ceasing to act and becoming brown masses. The body-wall then puts out a bud internally and forms a new polypide, which absorbs, or passes out, the brown body. The term of life of a single polypide is not known, but in every colony many such transformations are constantly taking place.

The colonies originally start from larvae produced in the /ovicells/ of the zoaria. The ovicells are sometimes very large and pear-shaped, occurring at intervals on the stems; or there may be one at the top of each zo[oe]cium. They look like pearls. A larva, when liberated, swims about for a time, then attaches itself to a fixed object, and increases, by budding, into some one of the various forms which the colonies take.

SUBCLASS =ECTOPROCTA=

ORDER =GYMNOLAEMATA=

SUBORDER ~CYCLOSTOMATA~

ERECT OR CREEPING POLYZOA

The zo[oe]cia are more or less cylindrical; the upper ends are sometimes completely free and sometimes closely adherent. The [pg194] opening of the cell has no operculum. Ovicells, containing the embryos, appear like pear-shaped swellings.

GENUS ^Crisia^

^C. eburnea.^ This species is found in tide-pools on algae,
especially on the red seaweeds, growing in bushy tufts from one
half of an inch to an inch high. Calcareous, with horny joints;
cells in two rows, semi-alternate, cylindrical, free at one end,
bent; no operculum; ivory-white; ovicells large and pear-shaped.
Common from Long Island Sound northward and on the Pacific coast.

GENUS ^Tubulipora^

^T. flabellaris.^ This species is found attached to slender
branched algae, in coral-like masses of long, crooked, tubular
cells united at the base and spreading into fan-shapes placed flat
against the fronds. It is sometimes one quarter of an inch in
diameter. On the same alga may often be found /Crisia/, /Mollia/,
and /Cellepora/. (Plate XLIX.)

GENUS ^Diastopora^

^D. patina.^ Tubular cells rise from a saucer-shaped disk about a
quarter of an inch in diameter; cells lie obliquely or stand erect,
and are crowded toward the center; margin of disk without cells;
colony white and calcareous. Found on algae and eel-grass from Long
Island Sound northward.

SUBORDER ~CHEILOSTOMATA~

In this suborder the zo[oe]cia are either horny or calcareous, and the orifices are usually surrounded with spines and have opercula. The orifices generally have raised margins, or peristomes. Ovicells form helmet-like coverings overhanging the orifices.

GENUS ^AEtea^

^AE. anguinea.^ Delicate, white, creeping, calcareous stems, from
which rise numerous club-shaped cells, about one eighth of an inch
high, each one with an aperture in the end. This species creeps in
wavy lines along the fronds of algae, and is frequently found on
/Dasya/, /Griffithsia/, /Plocamium/, and eel-grass.

GENUS ^Eucratea^

^E. chelata.^ A small, delicate species rising from a creeping
stem. It has branches composed of single rows of horn-shaped cells
having an oblique aperture on the side. Found at extreme low-water
mark on hydroids, shells, stones, and /Fucus/. (Plate XLIX.)

GENUS ^Cellularia^

^C. ternata.^ Zoarium filamentous, spreading, about one inch high,
white, calcareous, branched in a forking manner; cells long,
narrowest at base, arranged in series of three and on the same
plane, apertures oblique and facing one way; horny joint between
each cluster of cells. This species grows in deep water from Cape
Cod northward, and is found on objects washed upon the beach.
(Plate XLIX.)

GENUS ^Caberea^

^C. Ellisii.^ Zoarium erect, with fibrous base, leaf-like, branches
in a forking manner; branches straight, stiff, narrow, spreading;
cells arranged in rows of three, adherent throughout; long bristles
emanate from near base of many cells; egg-capsules globular,
smooth, pearly. Common from Cape Cod northward in deep water.
(Plate L.)

GENUS ^Bugula^

^B. turrita.^ This is a very abundant species, found everywhere
along the coast from Maine to North Carolina. Large quantities of
it are [pg196] sometimes thrown upon the beach by storms. It
grows in erect tufts, sometimes a foot long, and is much branched;
the branches grow around the stem in a spiral manner, forming
dense clusters. The lower part of the stem is often naked (having
lost the branches) and bright orange in color, while the tufts of
branches at the top are pearly-white or yellowish. The cells are
long, with a long, pointed spine on the upper outer angle. Like all
species of /Bugula/, it has bird-head appendages, which can be seen
under a powerful glass. (Plate L.)

^B. Murrayana.^ Clusters of broad, thin, flexible fronds, one
to two inches high, attached by a slender base and spreading in
entangled masses; fronds wedge-shaped, flat, dividing in a forking
manner; outer cells have bristle-like filaments, which constantly
beat the water; all cells have avicularia, or bird-head appendages.
(Plate L.)

^B. flabellata.^ Fan-shaped fronds of flat branches, divided in a
forking manner; the cells are arranged in four or five longitudinal
rows, are oblong, with a spine at each side of the circular
aperture, and are capped with pearl-like ovicells. This species,
like others of the genus, bears the very singular structures known
as avicularia, or bird-head appendages. They show, under a strong
glass, a hooked beak, like that of the hawk or parrot. These beaks
are attached by flexible stems and are provided internally with
powerful muscles by which they are constantly opened and closed;
the beak can bite with considerable force. In this species they are
attached to the sides of the cells. (Plate L.)

GENUS ^Flustra^

^F. membranacea.^ This species forms gauze-like incrustations on
the fronds of seaweeds, and is common on /Fucus/ and /Laminaria/,
spreading irregularly over several inches of space. The cells are
oblong, quadrangular, with a blunt, hollow spine at each angle.
Many specimens have simple horny tubes, closed on top, rising from
some of the cells to the height of half an inch. (Plate LI.)

GENUS ^Membranipora^

^M. pilosa.^ An incrusting variety, composed of a single layer of
cells spreading irregularly over the surfaces of stones, shells,
and seaweeds, sometimes completely covering the fronds of /Chondrus
crispus/, /Phyllophora/, /Rhodymenia/, and other algae. The cells
are membranaceous, with a calcareous rim, and have one long hair
and several small ones surrounding the large roundish apertures. It
is found in abundance on the shores from Long Island Sound to the
Arctic Ocean.

^M. lineata.^ Cells oblong, crowded, closely adherent; slender
spines on edge of aperture, which bend over and meet across it;
incrusts rocks and shells in broad, thin, radiating patches; cells
[pg197] much smaller and narrower than those of /M. pilosa/;
easily distinguished from that species by its manner of spreading
and the absence of the one long hair. Common from New Jersey
northward.

^M. tenuis.^ Common on pebbles, often covering their whole surface
with a lace-like incrustation of very small oblong cells having a
three-lobed aperture. Found in Long Island Sound and north to Cape
Cod.

GENUS ^Escharella^

^E. variabilis.^ This species forms calcareous incrustations on
shells or pebbles. The layers are thin, but eventually overlap one
another, and the incrustation sometimes becomes an inch thick and
resembles coral. The color of the living animal is dull red. The
species ranges from Cape Cod to South Carolina, and is abundant in
Long Island Sound.

GENUS ^Mollia^

^M. hyalina.^ Cells subcylindrical, irregular, transparent, smooth,
and more or less oblique. The species forms small circular disks on
algae in tide-pools.

GENUS ^Cellepora^

^C. scabra.^ It forms branching, coral-like masses on slender red
algae.

^C. ramulosa.^ Branches cylindrical, rough, dividing in a forking
manner, spreading, two to three inches high, calcareous; cells
urn-shaped, irregularly arranged, apertures contracted, long spine
on the outer edge. It is found in deep water attached to shells,
and in tide-pools, where it grows chiefly on /Sertularia/ and other
hydroids and on slender red algae. It ranges from Long Island Sound
to Greenland. (Plate LI.)

^C. pumicosa.^ Cells urn-shaped, irregularly crowded together,
forming a conglomeration of porous, brittle masses, not exceeding
an inch in breadth, usually round when small, oblong and knobbed
when large; spine on outer margin of aperture. It incrusts stones
and the stems of /Fucus/. (Plate LI.)

SUBORDER ~CTENOSTOMATA~

GENUS ^Alcyonidium^

^A. ramosum.^ Twelve to fifteen inches high; much branched;
branches smooth, cylindrical, one third of an inch in diameter,
usually crooked; branches in a forking manner; color rusty-brown.
Abundant in shallow water, attached to rocks, from New Jersey to
Cape Cod.

^A. hirsutum.^ A species common on seaweeds, sometimes completely
covering them, forming dirty, straw-colored, thick, cartilaginous
crusts covered with numerous conical papillae. These are the
cells, or zo[oe]cia; they are surrounded with spines. Circular
yellow spots occur over the surface, which are clusters of eggs.
A good pocket-lens will show the cells, laid in beautiful order,
and perhaps the extended tentacles. Found from Long Island Sound
northward. [pg198]

^A. hispidum.^ One of the most common species found incrusting
the fronds of /Ascophyllum/ at low-water mark. It forms fleshy,
brown, soft crusts of moderate thickness, and has spines scattered
over the otherwise smooth and glistening surface. The cells are
inconspicuous, and each one has five long rigid bristles. Habitat,
Long Island Sound to Greenland.

^A. parasiticum.^ It forms thin, earthy crusts on algae and
hydroids. The surface is porous; the cells are distant and arranged
irregularly, and seem as if composed of sand cemented with mud.

GENUS ^Vesicularia^

^V. dichotoma^ (^Valkeria pustulosa^). This species grows in
clusters of crowded slender stems, which branch in a forking
manner, the branches dividing in different planes, making a
tree-like form one to three inches high. At the points where the
branches divide is a dark, opaque substance, and at these points
also the cells are crowded in clusters of spiral rows and are
greenish-brown in color. The dark spots are in marked contrast to
the white translucent substance of the rest of the stem, giving a
spotted aspect to the whole. (Plate LI.)

^V. custata.^ Delicate, thread-like, jointed stems, with slender
opposite branches; cells small and elliptical, arranged mostly
in clusters. Found creeping like a small dodder-plant over other
polyzoans, hydroids, and seaweeds.

SUBCLASS =ENTOPROCTA=

GENUS ^Pedicellina^

^P. americana.^ A very small species. Club-like zo[oe]cia rise
from slender, white, creeping stems; tentacles roll up instead of
retracting into the cups. Found on hydroids, other polyzoans, and
algae.

V

ECHINODERMATA

Phylum
=ECHINODERMATA=

Classes
=ASTEROIDEA=
(/Starfishes/)

=OPHIUROIDEA=
(/Brittle-stars/)

=ECHINOIDEA=
(/Sea-urchins/)

=HOLOTHUROIDEA=
(/Sea-cucumbers/)

=CRINOIDEA=
(/Feather-stars and Sea-lilies/)

[pg201]

TERMS USED IN DESCRIBING THE STRUCTURE OF ECHINODERMS

^Abo'ral surface^: The side opposite the mouth.

^Ambula'cra^: Tubular feet used in moving.

^Ambulacral zones^: The five areas containing the rows of tube-feet.

^Ampul'lae^: Reservoirs or vesicles at the base of the tube-feet.

^Auricula'ta^: The larval stage of holothurians.

^Bipinna'ria^ or ^Branchiolaria^: The larval stage of starfishes.

^Dorsal surface^: The back of the animal, generally, but not
necessarily, the upper side.

^Exoskeleton^: Outside framework or support, differing from a true
skeleton which lies inside the body.

^Interambulacral areas^: The five areas between the ambulacral
zones.

^Larva^: The animal in a stage of development from the time it
leaves the egg until it reaches the complete form of the species.

^Madreporic plate^: A sieve-like plate of carbonate of lime.

^Oral surface^: The side on which the mouth is placed.

^Ossicles^: Calcareous plates which cover the body and form the
exoskeleton.

^Pedicella'riae^: Small spines which have divided ends, like
scissors or forceps.

^Plu'teus^: The larval stage of sea-urchins.

^Po'lian vessels^: One to ten sacs arising from the ring-canal.

^Ring-canal^: The canal around the mouth.

^Spines^: Processes which rise from the surface of the animal.

^Stone-canal^: A calcareous tube leading from the madreporic plate
to the ring-canal.

^Suckers^: Sucking-disks on the ends of the tube-feet.

^Ventral surface^: The side opposite the dorsal surface.

^Water-vascular system^: A series of canals which conduct water
through the animal. [pg202]

ECHINODERMATA

The echinoderms, although their shapes are very unlike in the different classes, have the same general internal structure, and also other features which place them together in one group. They are radiates (page 113) of the highest type; they have an exoskeleton; and many of them are beset with spines, from which the name is given. They have locomotor organs, the /ambulacra/, and a /water-vascular system/ peculiar to themselves. Some have the very strange power of casting off, and developing again, parts of the body.

The development from the egg to the adult is remarkable, and of unusual interest to naturalists. The larval stage of echinoderms is so unlike the mature animal that for a long time the larvae were thought to be another class of animals, and therefore were given the names which they still retain.

In observing echinoderms it will be seen that the dorsal part is carried uppermost by some, such as the starfishes and sea-urchins. In the former the back is broad and extended; in the latter it is curved and contracted. But in crinoids the back is carried downward and is extended like a stalk; in the sea-cucumbers (holothurians) the dorsal and ventral surfaces are parallel with the long axis of the cylindrical body, instead of being on a plane with the mouth and excretory opening. Owing to the unusual positions of the dorsal and ventral surfaces, the terms /oral/ (mouth side) and /aboral/ (side opposite the mouth) are generally used in describing these species.

The surface of the body is divided definitely by the ambulacra, the /ambulacral zones/, and the /interambulacral spaces/, but differently in the different classes. The movement of the animals is [pg203] effected by means of the tube-feet, or ambulacra. These have suckers, which are attached or released by the power of the water-vascular system. The /madreporic plate/, which can be distinctly seen in starfishes at the angle of two of the arms, is a calcareous porous plate which opens into the /stone-canal/. This canal passes through the body and opens into a circular tube which runs around the mouth. A system of canals extends from this circumoral tube, or /ring-canal/, and eventually one canal opens into each tube-foot. Water, entering by the madreporic plate, passes through the various canals and into the tube-feet, which it distends. When the feet are pressed against a substance and the water is withdrawn, a vacuum is formed, which causes the disk-ends of the feet to act like suckers. When the feet are again flooded the hold is relaxed. Thus the animal drags its body along with a slow, gliding motion. The madreporic plate, being calcareous, is said to act as a filter, purifying the water as it passes into the body, which it furnishes with oxygen as well as with locomotive power.