Chapter X: Part II: Marine Invertebrates (5)

The crinoids are inhabitants of deep water, where they grow in great numbers, forming beds of sea-lilies. Their general form, which suggests the lily, and their feather-like manner of branching, give them the two common names of sea-lilies and sea-feathers. They have a long, jointed stalk, one end of which is attached, while the other bears the disk of the animal. From the disk emanate five arms, which divide near the base, making [pg235] ten arms in all. The arms have short branches along the sides. Ambulacral grooves follow the center of all the arms and branches. The mouth is in the center of the upper side, which in this case is the ventral surface. The genus ^Pentacrinus^ remains permanently attached, but ^Comatula^, at a certain stage of development, separates from the stalk and swims freely about by means of its arms. It can attach itself temporarily by tubular processes, which are developed on the dorsal surface at the point where the stem was attached. The ossicles, or plates which cover the dorsal surface, are free, making the crinoid an animal of innumerable joints.

The crinoids are particularly interesting from the fact that they have existed from early geologic times, and their history is written in stone. In the early ages they were the only class of echinoderms, and their evolution into other forms can be traced through successive geologic periods. They existed in such vast numbers that the fossil forms are plentiful and are familiar to every student of geology, and are known as stone-lilies and encrinites. To-day they are decadent, there now remaining only twelve of the two hundred genera which existed formerly. A fine bed of crinoids is found off Cuba, on the slope of the coast where the water rapidly deepens from one hundred to two hundred fathoms. [pg236]

Although the crinoids are deep-water forms, and are never found on the beach, they are given here because they follow in the system of classification and illustrate another curious class of echinoderms. The brief description given may add interest to the fossil forms to be seen in museums.

VI

ARTHROPODA

TABLE SHOWING THE CLASSIFICATION OF THE ARTHROPODS DESCRIBED IN THIS CHAPTER

Phylum =ARTHROPODA=

Class =CRUSTACEA=

Subclass =Entomostraca= (/Crustacea of small, often of almost
microscopic minuteness, and of comparatively simple
organization; appendages have little differentiation/)

Order =PHYLLOPODA= (/Appendages resemble leaves; mostly
fresh-water species/)

Suborder ~EUPHYLLOPODA~ (/Phyllopoda of considerable
size, bearing ten to sixty pairs of leaf-like
swimming-feet/)

Suborder ~CLADOCERA~ (/Small phyllopoda; body laterally
compressed; carapace like a bivalve shell; four to five
pairs of swimming-feet; chief organs of locomotion are
the biramous antennae; abdomen devoid of appendages. They
abound in fresh water, are very prolific, and afford a
large amount of food to fresh-water fishes/)

Genera Species

^Daphnia^
^Leptodora^
^Moina^
^Polyphemus^

Order =OSTRACODA= (/Resemble minute bivalve shells; swim by
antennae; body unsegmented; appendages seven pairs only/)

^Cypris^ (fresh-water)
^Cypridina^ (marine)

Order =COPEPODA= (/Small size; body long, segmented; four to
five pairs of once-branched appendages on thorax; abdomen
without appendages; abundant in fresh and salt water; many
forms parasitic/)

^Cyclops^
^Cetochilus^
^Sapphirina^
^Siphonostomata^
^Nicothoe^

Order =CIRRIPEDIA= (/Imperfectly segmented; fixed or
parasitic during adult life; inclosed in skin strengthened
by calcareous plates; abdomen rudimentary; appendages
biramous, usually six pairs/)

Genera Species

^Lepas^ ^L. anatifera^
^L. striata^
^L. pectinata^

^Balanus^ ^B. balanoides^
^B. eburneus^
^B. rugosus^
^B. geniculatus^
^B. tintinnabulum^

Suborder ~RHIZOCEPHALA~ (/Parasitic/.)

^Sacculina^ (parasitic on crabs)
^Peltogaster^ (parasitic on hermit-crabs)

Subclass =Malacostraca= (/Highly organized Crustacea, usually
of considerable size; appendages much differentiated/)

Order =PHYLLOCARIDA= (/Small; covered with bivalved carapace;
thoracic feet leaf-like; abdominal feet biramous; posterior
segment terminates in two long spines; mostly fresh-water
species/)

Order =SCHIZOPODA= (/Small; transparent; shrimp-like; thorax
more or less completely covered with soft carapace;
thoracic appendages biramous; eyes on stalks/. /Mysis/ are
/Without gills or thoracic legs/; /Euphausia/ are /With
gills or thoracic legs/.)

^Mysis^ ^M. sternolepis^
^Euphausia^

Order =DECAPODA= (/Thoracic segments unite with head and form
cephalothorax, which is covered by carapace; eyes stalked;
maxillipeds have exopodites; five pairs of walking-feet
without exopodites/)

Suborder ~MACRURA~ (/Abdomen usually longer than
cephalothorax and commonly extended; rostrum usually
prominent; eyes not inclosed in orbits; antennae and
antennules large; antennae have exopodites/)

Set Free-swimming Forms: Shrimps and Prawns

^Penaeus^ ^P. setiferus^
^P. brasiliensis^
^Palaemonetes^ ^P. vulgaris^
^Crangon^ ^C. vulgaris^
^C. franciscorum^

Families Genera Species

Set Creeping Forms: Lobsters and Crawfish

ASTACOIDAE ^Homarus^ ^H. americanus^
^Panulirus^ ^P. interruptus^
^P. argus^
^Scyllarus^

Set Anomalous Forms: Approaching the Brachyura

Suborder ~ANOMURA~ (Of these Families, the Lithodidae have
/Fifth pair of feet folded under the carapace/)

DROMIDAE ^Hippoconcha^ ^H. arcuata^

PAGURIDAE ^Pagurus^ ^P. bernhardus^
^P. pollicaris^
^P. longicarpus^
^Clibanarius^ ^C. vittatus^
^Pylopagurus^

CENOBITIDAE ^Cenobita^ ^C. diogenes^

HIPPIDAE ^Hippa^ ^H. talpoida^
^H. analoga^
^Albunaea^ ^A. gibbesii^

PORCELLANIDAE ^Porcellana^ ^P. sayana^
^P. sexspinosus^
^Petrolisthes^ ^P. armatus^

LITHODIDAE ^Lithodes^ ^L. maia^
^Echidnocerus^ ^E. cibarius^
^E. foriminatus^
^Acantholithodes^ ^A. hispidus^
^Cryptolithodes^ ^C. sitchensis^
^Phyllolithodes^ ^P. papillosus^

Suborder =BRACHYURA= (/Abdomen shorter than cephalothorax,
and permanently folded under it; eyes inclosed in orbits;
antennules and antennae small/. Of these Families, the
PORTUNIDAE are called /Swimming crabs/; the OCYPODIDAE are
called /Sand- and fiddler-crabs/; and the MAIIDAE are the
so-called /Spider-crabs/.)

Families Genera Species

PORTUNIDAE ^Carcinides^ ^C. maenas^
^Callinectes^ ^C. sapidus^
^Ovalipes^ ^O. ocellatus^

Set WALKING CRABS

CANCROIDAE ^Cancer^ ^C. irroratus^
^C. borealis^
^C. magister^
^C. productus^
^C. antennarius^
^Menippe^ ^M. mercenaria^
^Eupanopeus^ ^E. herbstii^
^Eurypanopeus^ ^E. depressus^
^Neopanopeus^ ^N. texana^
^Rhithropanopeus^ ^R. harrisii^

GRAPSIDAE ^Hemigrapsus^ ^H. nudus^
^H. oregonensis^
^Pacygrapsus^ ^P. crassipes^

OCYPODIDAE ^Ocypoda^ ^O. arenaria^
^Uca^ ^U. minax^
^U. pugnax^
^U. pugilator^

MAIIDAE ^Libinia^ ^L. dubia^
^L. emarginata^
^Hyas^ ^H. coarctatus^
^H. lyratus^
^H. araneus^
^Loxorhynchus^ ^L. crispatus^
^Pugettia^ ^P. gracilis^
^Sternorhynchus^ ^S. sagittarius^
^Epialtus^ ^E. productus^
^Pitho^ ^P. aculeata^
^Lambrus^ ^L. pourtalesii^

CALAPPIDAE ^Calappa^ ^C. flamma^

PINNOTHERIIDAE ^Pinnotheres^ ^P. ostreum^

Order =STOMATOPODA= (/Abdomen very large; second pair
of thoracic legs very large; gills borne on abdominal
segments/)

^Squilla^ ^S. empusa^

Order =CUMACEA= (/Small, shrimp-like/)

^Diastylis^ ^D. quadrispinosus^

Order =ARTHROSTRACA= (/No carapace, as a rule; six to seven
pairs of walking-legs; eyes sessile/)

Suborder ~AMPHIPODA~ (/Body usually compressed laterally/)

^Orchestia^ ^O. agilis^
^Talorchestia^ ^T. longicornis^
^Gammarus^ ^G. locusta^
^Chelura^ ^C. terebrans^
^Caprella^ ^C. geometrica^

Suborder ~ISOPODA~ (/Body depressed or flattened/)

^Cirolana^ ^C. concharum^
^Limnoria^ ^L. lignorum^
^Sphaeroma^ ^S. quadridentatum^
^Idotea^ ^I. marina^
^I. ochotensis^
^I. metallica^
^I. wosnesenskii^
^Chiridotea^ ^C. caeca^
^C. entomon^

Class =MERISTOMES=

Order =XIPHOSURA=

^Limulus^ ^L. polyphemus^

Class =PANTOPODA= (Lang)

Order =PYCNOGONIDA=

^Phoxichilidium^ ^P. maxillare^

[pg243]

TERMS USED IN DESCRIBING CRUSTACEA

^Abdomen^: The posterior part of the body.

^Antennae^: Articulated appendages which immediately precede the mouth.

^Anten'nules^: The anterior of the two pairs of feelers of the head.

^Bira'mous^: Having two branches.

^Carapace^: A thin chitinous shell covering the cephalothorax.

^Cephalic^: Pertaining to the head.

^Cephalotho'rax^: The united head and thorax.

^Chela^: The pair of pincers, or claw, which terminates some of the appendages.

^Che'liped^: A leg with chela, or claw, at the end.

^Endop'odite^: The inner one of the two main divisions of the limb.

^Epime'ra^: Divisions on the ends of the segments of amphipods and isopods, and belonging to the legs.

^Epip'odite^: A third branch of a limb.

^Epis'toma^: A triangular area in front of the mouth.

^Exop'odite^: The outer one of the two main branches into which the typical limb of any segment is divided.

^Gastric mill^: The first half of the stomach, where food is ground.

^Mandibles^: The pair of appendages next behind the antennae.

^Maxil'lae^: The first pair of appendages after the mandibles.

^Maxillipeds^: The three pairs of appendages after the maxillae.

^Metame'res^: Segments.

^Orbits^: Eye-cavities, peculiar to the higher /Crustacea/.

^Prosto'mium^: The region in front of the mouth; the preoral part of the head.

^Rostrum^: The beak in front of the head.

^Segment^: A part cut off or marked as separate from others.

^Somite^: A segment of the body.

^Squame^: A scale.

^Telson^: The last segment of the abdomen.

^Thorax^: The middle part of the body.

[pg244]

ARTHROPODA

This subdivision of the animal kingdom includes insects, centipedes, spiders, and crustaceans, which together constitute more than half the known species of animals. Although these animals are so unlike in general appearance, it is easy to recognize the common characteristics which place them together in one group. The name /Arthropoda/, meaning "jointed-footed," suggests perhaps one of the most obvious points of resemblance. The /Arthropoda/ have bilateral symmetry, one side of the body being like the other; they are covered with a horn-like material (chitin); they are divided into segments; the segments have appendages; and the appendages are jointed so as to admit freedom of motion. Their manner of growth is peculiar; they cast off their rigid external coverings and secrete larger coats of mail, and at these periods increase in size or undergo metamorphosis.

There are such modifications of these general features as the habits of the different species demand. For instance, the appendages may be constructed for walking, swimming, boring, sucking, or the seizure and preparation of food. In some animals the appendages form a part of the breathing-organs, in others are used as organs of sense. Every detail of the organism, down to the hairs, has its special use and function.

CLASS =CRUSTACEA=

The crustaceans vary in size from microscopic minuteness to two feet or more in length. The giant crab of Japan (/Kaempferia kaempferi/) exceeds this, being commonly from eight to twelve feet [pg245] across the arms, and is said to reach even greater proportions. Crustaceans live on land and sea, and in both fresh and salt water; they may be parasitic, sedentary, or free and active. There are said to be over ten thousand species, which include crabs, lobsters, shrimps, beach-fleas, wood-lice, barnacles, and water-fleas. Nine tenths of the species are marine; of these some are pelagic, and their transparent forms constitute a part of the plankton. Others live on the bottom in deep water and attain a large size. A vast number live in the littoral zone and form a considerable part of that crowded community. They are scavengers and freebooters, being great fighters, as well as predatory in their habits. As a rule, they feed on dead organic matter, which they consume in surprising quantities; some have also a vegetarian diet. They have, like starfishes, the singular power of throwing off their limbs and growing new ones.

The /Crustacea/ derive their name from the nature of their crust or covering. This is earthy and brittle, not stony, like the shells of mollusks. This crust, or exoskeleton, has various degrees of firmness, from that of a delicate polished cuticle, seen in small forms, to the heavy armor of some crabs and the shell-like character of the covering of barnacles.

The lobster and crab are perhaps the most comprehensive examples as well as the largest in size of the class, the vast majority of the species being minute forms. The ocean swarms with varieties too small to be noticeable to the naked eye.

It is the province of /Crustacea/ to consume decaying organic matter, both animal and vegetable, and in doing this they perform a great service in purifying the waters of the pool, the shore, and even the sea. Not only in this are they serviceable, but to a great extent they serve as food for other animals, their flesh being palatable and preferred to that of other animals whose diet would seem to make them more wholesome. The small forms exist in such myriads, and increase so rapidly, that, although extremely small, they furnish an inexhaustible supply of food. Even some whales subsist upon these minute animals, and for man the larger species are articles of diet that are counted among the luxuries. The crustaceans are remarkable for their varied forms and for their [pg246] perfect adaptation to many different conditions of life. There is no class in the animal kingdom which presents so wide a range of organization, or whose structure deviates so widely from the type form. These differences lie chiefly in the external characters and in the structure of the appendages.

Some species are solitary, like lobsters and crabs; others, like shrimps, are gregarious and live in immense shoals. In the habits of these animals there is much which excites wonder and interest.

ANATOMY OF THE HIGHER CRUSTACEA

The body of a crustacean is divided into segments, which are sometimes distinctly separated, like joints, and sometimes fused into one piece. The head part is called the /cephalic/ portion, the middle section is the /thorax/, and the posterior part is the /abdomen/. The horn-like covering of the thorax is the /carapace/; where it projects over the head it is the /rostrum/. When the head and thorax are united, as in most /Crustacea/, the anterior or front portion of the animal is called the /cephalothorax/. Each segment has a pair of appendages. Each appendage has a joint attached to the body; from this arise two jointed branches, the /endopodite/ and the /exopodite/, the inner and the outer foot. The appendages are modified to perform special functions. In front of the mouth are two pairs: the smaller ones are the /antennules/ and have ears at the base; the larger ones are /antennae/ and are feelers. At the base of the antennae are the /green glands/, said to have renal functions. Both the antennules and the antennae are fringed with hairs, which aid in the sense of touch and perhaps of smell. On each side of the mouth are the /mandibles/. Then come the /maxillae/ and the /maxillipeds/, used in capturing and tearing the food and conveying it to the mouth. Thus it will be seen that some of the appendages around the head are connected with the senses, and others are used in eating. Those of the thorax are for walking; those of the abdomen for swimming, guarding the eggs, etc. The food taken into the mouth passes into the stomach through a short passage. The stomach is divided into two parts. The front [pg247] one contains three long teeth which meet laterally and grind the food; this is known as the /gastric mill/.

When sufficiently fine, the food passes through a strainer of stiff bristles into the smaller portion of the stomach, where it is partially digested, and from there enters a long, straight intestine which reaches the length of the body and opens to the outside on the under side of the /telson/, or last segment. A large liver also pours its secretions into the intestine. The green substance commonly called "fat" in lobsters is the liver.

The heart consists of an elongated tube, or a short sac, which lies directly under the integument of the back. From this heart-sac, blood, which is colorless, is sent by arteries to all parts of the body; it then collects in spaces called /venous sinuses/, from which it goes to the gills, and thence back to the heart.

The nervous system begins in a large ganglion in front of the mouth, called the brain; from this two branches arise, which pass on each side of the digestive organs, meeting in ganglia in each segment and extending the whole length of the body. The gills, by which the animal breathes, are upon the limbs, or on the walls of the body immediately adjacent to them, and are generally inclosed in special chambers. In lobsters and crabs two such chambers are found under the flaps of the carapace, above the walking-legs. Gills are divided so as to present much surface to the water, from which they absorb oxygen. They are like a dense mass of little tubes arranged along a central tube. The class has two kinds of eyes, simple and compound; the latter are composed of a number of eyes. In some species the eyes are placed on the ends of movable stalks, which enable the creature to see in all directions and from a higher plane than the body occupies. As a rule, the eyes occur in the head region, but in the shrimp /Euphausia/ they are on the thorax and abdomen. In barnacles simple eyes exist in the young stage, but in adult forms there are no apparent visual organs. The ear (so called) consists of a sac containing small silicious particles suspended in fluid. Numerous fine hairs on the inner surface of the sac connect with nerve-fibrils.

The organs of hearing are in various places. In decapods, or the larger /Crustacea/, they are at the base of the antennules. [pg248]

The muscles are white bundles of fibers, and are in strips, which is an indication of power and activity. There are four important sets: twisted ventral muscles which bend the tail and are particularly large and strong, those which straighten the tail, those moving the appendages, and those which work the gastric mill.

The eggs, after being discharged, are attached to the abdominal legs of the mother by a kind of cement, or they are carried in pouches attached to the thorax. In these positions they mature, and hatch at different stages of development in different species. Some emerge with three pairs of legs, and are known as /Nauplius/; some are /Zoea/, having a carapace and abdominal segments, but no abdominal appendages. Another stage is /Megalops/, with large stalked eyes. Others are hatched as miniature adults. These names were given when the embryo stage was not recognized and the larvae were thought to be distinct species.

The growth of the animal is effected by moulting. The /Crustacea/ are named from the crust-like covering which envelops them. It is a horny material, called chitin, in which are deposited particles of carbonate of lime, making a rigid envelop which would prevent all freedom of motion, were it not that there are spaces free from lime, and thus flexible joints are left. When the animal expands it throws off this hard covering and secretes a new and larger one. As the time of moulting approaches, the old covering becomes loosened, and a delicate new one is formed beneath it. The old shell splits open across the back just behind the carapace, and the soft animal withdraws first its cephalothorax and then its abdomen, leaving the cover complete, including even the covering of the eyes and the lining of the stomach. The [pg249] new shell is rapidly hardened, being already formed when the old one is cast, and the animal regains its normal condition in about a week; in the meantime it is defenseless, and lies quiet in some secluded place. Moulting is an exhausting process, and is attended with great dangers. A great mortality occurs at this time from accidents, from weakness, and also from helplessness in case of attack.

The hair-like processes scattered over the shell, often like fringes, are said to be organs of feeling.

SUBCLASS =ENTOMOSTRACA=

These are /Crustacea/ of small, often microscopic size, of comparatively simple organization, and with appendages adapted to serve the purpose of respiration. These minute animals may be obtained by skimming the surface of the water with a muslin net, preferably at night, then washing off the inside of the net with a small quantity of water into a glass dish. Place the dish on a dark surface before a light, and the little creatures will gather toward the light, and may be satisfactorily observed with a glass.

ORDER =COPEPODA=

This order, though composed of minute forms, is one of great economic importance, from the fact that the little crustaceans exist in vast numbers and furnish a very considerable part of the food of many fishes. ^Cyclops^ is the most common of the fresh-water, and ^Cetochilus^ of the marine genera. These, together with other genera, swarm in water wherever life exists, from the smallest pools and ditches to the broad surface of the ocean. Without having drawn a surface-net on some sheltered bay, it is difficult to have an idea of the myriads of /Entomostraca/ in the sea. Although nearly transparent and of such delicate texture as to be almost jelly-like, they sometimes color the sea with a reddish tint for miles. Whales which have baleen, or fringes of whalebone, in the mouth subsist on these small organisms, which are called "brit" by the whalemen. The whales, sometimes in schools, rush through the water with open mouths, engulfing these little [pg250] crustaceans, the baleen straining them from the water. Although devoured in such immense quantities, and sometimes lying dead in sheets of scum on the surface of the water, they maintain their numbers by the exceeding rapidity with which they reproduce. It has been computed that the descendants of one /Cyclops/ may number in one year 4,500,000,000, provided all the young reach maturity and produce a full number of offspring.

One of the free marine forms, ^Sapphirina^, is of especial interest, as it surpasses all animals in phosphorescence and sparkles by day as well as by night. It is one quarter of an inch long, and is broad and flat.

Besides the myriads of free-swimming copepods, there are parasitic forms in great number. The marine parasitic forms are commonly known as fish-lice. They have various habits, some living as commensals, others attaching themselves to animals only to be carried about; the true parasites live upon the blood and tissues of their hosts, and may fasten themselves to the external parts of the body or to the internal organs. Whales, fishes of all kinds, mollusks, starfishes, jellyfishes, and corals, all have some form of parasite, and many have several different kinds of guests. It is said that the haddock has more than a dozen which infest its external and internal membranes.

^Nicothoe^ is found on the gills of lobsters. The truly parasitic forms are usually very degenerate and lose the characteristics of their order.

ORDER =CIRRIPEDIA=

("/Curled feet/")

THE BARNACLES

Barnacles of the genus /Balanus/ (acorn-shells) (Plate LIX.) are familiar objects on rocky shores, which they often whiten with their shells, and those of the genus /Lepas/ are also widely known. The name of the order is descriptive of their curled appendages. The appendages are fringed like feathers and are drawn into or protruded from the shell at will. When extended they are constantly in motion, and create currents which carry food to the [pg251] mouth of the animal, which is dependent upon such food as comes within range of its tentacles.

Their life-history is interesting. The young barnacle, called a /nauplius/, in no way resembles the adult. When it emerges from the egg it is a free and independent animal, with one eye, three pairs of legs, and a single shell. It swims about for a while and moults several times. It then has two eyes, two shells, and six pairs of legs. At this period it seeks a permanent home, and attaches its anterior end to the object it selects by means of its antennae, which have become suckers. It makes its hold secure by secreting a cement which permanently fastens it to the spot. It then undergoes metamorphosis, loses its bivalve shell and its eyes, and attains its characteristic /cirripeds/, or curled feathery legs, and a new shell covering. During these transformations, from the time it becomes fixed until it attains its adult form, the barnacle fasts, living by the absorption of its own animal fat. Its food subsequently consists of the minute animal forms which abound in the sea. Its further growth is by moulting, but parts only of its covering are disengaged; the shell is permanent, and its successive stages of growth are marked upon it by lines, as in mollusks. The lining of the shell, or enveloping skin of the animal, and also the cuticle of the legs are [pg252] shed, and in the spring of the year these thin, glossy casts are found in abundance floating on the surface of the water near the shore.

There are but three orders of barnacles, namely, those in which the shell is directly attached to the rocks, those which are attached to floating objects by a long stalk, and those which are parasitic on animals. A species of the third order infests the whale.

The older zooelogists classed barnacles with the /Mollusca/, but in 1829 Vaughan Thompson, in the study of their embryology, found that they should be classed with crustaceans, in company with crabs, shrimps, and water-fleas, with which their immature forms show direct relationship.

GENUS ^Lepas^

This genus is commonly known as the ship-barnacle, also as the goose-barnacle. It attaches itself to floating logs as well as to ships, but the latter form its principal home; consequently it is a great voyager, and, though common everywhere, is everywhere considered a stranger. The same species are found on ships coming from the most remote and widely separated regions, and so they cannot be considered native to any one locality. They are wanderers on the deep, and grow in such numbers on the bottoms of ships, especially of those which sail in warm seas, that they seriously impede the progress of the vessels. Aside from diminishing its speed, they do a ship no injury.

There was a tradition, which lasted several centuries, that geese were hatched from these shells, which somewhat resemble eggs. Gerard, in the appendix to his "Herball or Generale Historie of Plants" (1597), gives a picture of shells of /Lepas/ growing on a tree, with geese falling from them and swimming about in the water below. His description is as follows: "There are founde in the North parts of Scotland and the islands adjacent called Orchades certaine trees whereon do growe certaine shell fishes of a white color, tending to russet, wherein are conteined little living creatures; which shells in time of maturitie do open, and out of them grow those little living foules whom we call barnakles, in the North of England brant geise, and in Lancashire tree geise; but [pg253] the other that do fall upon the land do perish and come to nothing." He then describes in detail the various transformations, and ends with: "But what our eies have seen and hands have touched we shall declare."

The long, flexible stalk of /Lepas/ is its anterior end. Generally this stalk is only half an inch long, but in some species it attains the length of a foot.

Huxley describes the barnacle as a crustacean fixed by its head and kicking food into its mouth with its legs. The mouth has a pair of small mandibles and two pairs of maxillae, the last pair uniting to form a lower lip. The thorax has six pairs of branched appendages. The body is enveloped in a fold of skin, to which are attached five shell-like plates. One of these plates is long and narrow, and extends along the dorsal side; two are large and triangular (the terga); two are small and triangular (the scuta), the long point extending downward. These shells are on the free or posterior end.

Barnacles have a nervous system, consisting of a brain and a chain of five or more ganglia, but no special respiratory or circulatory organs are known; the cirripeds, or feet, are supposed to perform these functions. They have also a food-canal, a digestive gland, and excretory tubes. The eggs are carried under the external fold of the skin in flat cakes.

^L. anatifera.^ The shell is bluish-white, showing lines of growth
and faint radiating lines emanating from the anterior basal angle.
The upper valves are narrow; the long tips point downward, and
the top is blunted, leaving a space which is occupied only by a
membrane. Near the apex of the shell, at the back, is a distinct
angle. The dorsal valve is broad, not much compressed, and is
sometimes grooved lengthwise. The cartilage of the shell and
the stalk adjoining the shell are orange-colored. The stalk is
grayish-brown and the cirri flesh-colored. The stalk is from one
inch to six inches long. The shell is one inch long.

^L. striata.^ Shells bluish-white; valves sharply triangular;
dorsal valve compressed, forming a ridge; lines radiate from the
basal angle of the lower valves and from the upper angle of the
terminal valves, starting from the extreme end; the margins have a
narrow edge of yellow cartilage; the stalk and cirri are of a dark
slate-color; shell and stalk are each about an inch long.

^L. pectinata.^ Shell shorter and less compressed than in the
preceding species; lines of growth and radiating lines distinct; a
decided line [pg254] runs from anterior base to summit, a little
back of the margin; terminal end broadly obtuse (truncated); dorsal
valve much compressed, forming a sharp edge serrated with ten to
twelve teeth and distinctly striated or furrowed.

GENUS ^Balanus^

/Balanus/ is known as the "acorn-shell," or "sea-acorn," and is found in vast numbers and of all sizes between tide-marks, incrusting rocks and the piles of piers. It also may be found attached to floating objects or to shells, or even to living animals, but its usual habitat is stationary. Unlike /Lepas/, it has no stalk, the shell being directly attached to some object. The body is surrounded by a fold of skin, to which are attached a shell consisting of six or more plates and a fourfold lid, or /operculum/, consisting of two /scuta/ and two /terga/. The operculum may be called the door, as the animal opens and shuts it at will and has complete protection when it is closed. If one taps a rock [pg255] incrusted with barnacles, and holds the ear near, the closing of the many doors may be distinctly heard.

The development of /Balanus/ from the larval stage, as also the anatomy of the adult, is similar to that of /Lepas/. When covered with water and unmolested, there may be seen over a bed of barnacles thousands of tiny fringed feet waving to and fro. The motions look like gestures; they are perfectly regular and rapid, numbering eighty to a hundred a minute. The shell covering formed by barnacles on piles of wharves and bridges is said to be a protective agent; otherwise the barnacles seem to have no economic value in nature, as, unlike other animals, they do not serve, except in very small measure, as food to other classes. The tautog and perhaps some other fishes feed partly upon them. They are sometimes an obstacle to oyster-culture, as they fasten upon the objects intended for oyster embryos, and, growing faster than the latter, soon crowd them off. One species, /Coronula diadema/, fastens to the skin of whales. It attains the size of two inches in diameter. The shell is half an inch thick and full of cavities, into which the skin of the whale is drawn, giving the barnacle a secure hold. (Plate LIX.)

^B. balanoides^ (Stimp.), ^B. ovularis^ (Gould), the rock-barnacle.
This is perhaps the most conspicuous of the barnacles. It inhabits
the whole northern Atlantic coast, and is so abundant that it not
only whitens the rocks with a complete incrustation of shells, but
the animals are so crowded that many of them lose their normal
shapes and become greatly elongated. When the rocks are covered
with water they seem alive, on account of the thousands of waving
tentacles. This species also incrusts woodwork between tide-marks.

The shell is small, white, and variable in shape; sometimes its
height is less than the diameter of its base; again the height is
several times greater and the summit broader than the base. In its
early stages the valves are smooth, but later the base is scalloped
by four or five grooves. The summit of the plates is even and
blunt. The aperture is diamond-shaped. Two valves of the operculum
are pointed at the tips; two are blunt, making a deep notch in
the summit. These valves are the distinctive feature by which to
recognize this species, which varies so much in outward form; the
species is also distinguished by its membranous base, which does
not form a solid plate like that of other species.

^B. eburneus^, the ivory barnacle. This species, like /B.
balanoides/, is a very common barnacle, and is found on all kinds
of submerged woodwork, whether fixed or floating. It is also found
on the carapace of [pg256] crabs and /Limulus/, and on mollusks.
It is chiefly found on objects below low-water mark. It ranges
from Massachusetts Bay to Florida. It is easily distinguished from
the preceding by its low, broad form and shelly base. The shell is
smooth and circular at the base, and inclines backward, forming an
oblique cone with a triangular opening; the plates terminate in
points at the summit and incline backward, the last one forming a
kind of beak. The operculum is pyramidal; two of its valves have
both transverse and longitudinal lines well defined at the base,
and are coarsely toothed at the edges; the posterior valves are
slightly grooved across.

^B. rugosus^ (Gould), ^B. crenatus^. Shell white, cylindrical,
somewhat conical, rugged, the summit usually as broad as the base;
height often greater than diameter; aperture diamond-shaped, plates
ending at the summit in acute spreading points, the posterior plate
folded and curved like a beak; plates rough, with coarse, irregular
ribs; valves of the operculum at the summit acute, with diverging
points; the points striated. Found on shells and stones in deep
water and also on bottoms of ships.

^B. geniculatus.^ Shell dirty greenish-white, cone-shaped; aperture
about the size of base; shell-plates triangular, unequal in
breadth, and with alternate large and small ribs; the smaller ribs
compressed and roughened on the edges by the conspicuous lines of
growth which run across them; depressed areas between the plates
marked with fine cross-lines; front valves of the operculum have
coarse plated ridges, which incline over one another and are
crossed by fine radiating lines; diameter at base one to one and
a half inches; height two thirds the diameter. Found on pecten
shells, and abundant off the coast of Maine.

^B. tintinnabulum.^ Shell pink to purplish, conical, with six
triangular plates, which are grooved, forming unequal ribs, and
crossed by distinct lines of growth; spaces between plates crossed
by lateral lines; posterior valves of the operculum longer than the
others and curved forward, resembling the beak of a bird of prey;
diameter at the base one inch; height one and a half inches. Found
in warm waters and on vessels from the South.

SUBORDER ~RHIZOCEPHALA~

These are parasitic forms and very degenerate. ^Sacculina^ lives on crabs, and its term of life is about three years, during which period the afflicted crab does not moult. Its shape is that of an ovoid sac on a stalk, which it attaches between two segments of the ventral surface of its host. The stalk divides and ramifies in a root-like manner within the body of the crab, from whose vital elements it absorbs its nourishment. The roots spread like a mycelium through the whole crab, even to the claws.

^Peltogaster^ lives on hermit-crabs. [pg257]

SUBCLASS =MALACOSTRACA=

This subclass comprises highly organized /Crustacea/, usually of considerable size, having the appendages much differentiated, the thorax with eight segments, and the abdomen with seven segments.

ORDER =SCHIZOPODA=

The name, meaning "cleft-footed," applies to the appendages of the thorax, which are once-branched (/biramous/). Gills, when present, are attached to these feet, and hang freely in the water. A delicate carapace covers the thorax; the abdomen is proportionately very large, often twice the length of the cephalothorax. In /Mysis/ the eggs are carried in pouches under the thorax, giving the common name of "opossum-shrimp" to this small, transparent, phosphorescent crustacean.

GENUS ^Mysis^

^M. sternolepis.^ About one inch in length; translucent; antennae
very long; segments marked at joints with dark spots; the last two
segments terminate in a stout spine; telson longer than the sixth
segment; the sides are nearly straight and are armed with spines;
the extremity is cleft; eyes large and prominent. Found abundantly
in winter on the shores of still, muddy bays and sounds, especially
among eel-grass.

ORDER =DECAPODA=

("/Ten-footed/")

The /Decapoda/ are named from their ten walking-legs. The higher forms of crustaceans belong to this order. All the /Decapoda/ have a similar anatomy, but are placed in two subdivisions [pg258] according to their external form. In /Macrura/, the first subdivision, belong the lobsters, crawfish, shrimps, prawns, and hermit-crabs, animals having a long and more or less cylindrical body, with the abdomen extended; in /Brachyura/, the second subdivision, are placed the crabs, animals having the thorax broad and flat, and the abdomen bent under the thorax. The /Decapoda/ have twenty segments, all of which, except the last one, have, at some period of life, a pair of appendages. The first two pairs of appendages, or, in the stalk-eyed forms, the first three pairs, are especially connected with the senses, and are often fringed with hairs, which are also considered to have a sense-function. The /antennules/, or first pair of appendages after the eye-stalks, are sometimes divided into two or three branches. At the base of the antennules are the ears. The /antennae/, or second pair of appendages, are undivided, but are larger than the first pair, and are often very long. At the base of the antennae are the renal glands. Both the antennules and the antennae are slender, elongated, movable, and full of joints. In some species they are greatly modified, as in /Scyllarus/, where they are developed into broad swimming-plates and, perhaps, as shovels for burrowing; in some amphipods they are used as swimming-organs. (Plate LX.)

The next six pairs of appendages are grouped about the mouth. They are the /mandibles/, the /maxillae/, and the /maxillipeds/. The mandibles are at the mouth-opening, and, being heavy and hard, are adapted to tearing and grinding; they have a jointed attachment, the /palpus/, whose office is to keep the mandibles clean. The two pairs of maxillae are delicate and leaf-like. The three pairs of maxillipeds grow gradually larger, the last pair being very prominent and extending over the other mouth-parts. Next come five pairs of walking-feet. One or more pairs of these feet have pincer-like ends, or claws. Some species have the claws immensely developed, as in lobsters. The claws are the /chelae/, and the feet which bear the /chelae/ are termed the /chelipeds/. The rest of the walking-feet have generally single, hook-like ends, but are variously modified in different species. The abdominal segments have six pairs of appendages, also variously modified. The last segment is without appendages, but often is extended into a tail, [pg259] or fin-like expansion. The next to the last segment, in many forms, has appendages modified into swimming-plates, which extend on each side of the telson, forming a broad, fan-like caudal extremity.

They have, then, to correspond to the twenty segments of the body, two pairs of sensory, six pairs of mouth-, and five pairs of walking-appendages attached to the cephalothorax, and six pairs on the abdomen. The terminal segment, or telson, is without appendages. The exopodite is present on the maxillipeds, but disappears from the walking-feet in the higher forms.

In moulting the /Macrura/ split in the longitudinal line down the back; in the /Brachyura/ the split occurs across the body at the point between the thorax and the abdomen.

SUBORDER ~MACRURA~

SHRIMPS, PRAWNS, LOBSTERS, CRAWFISH, AND HERMIT-CRABS

The characteristic features of the /Macrura/ are an elongated body with the abdomen usually extended; a carapace, somewhat cylindrical; and the last pair of appendages of the abdomen (which are attached to the next to last segment) united with the last segment, or telson, to form a powerful caudal fin, used for swimming backward. The creeping forms in moving walk forward, but swim backward.

FREE-SWIMMING FORMS: SHRIMPS AND PRAWNS

In these animals the body is compressed and the carapace is not hard. The abdomen is very large in proportion to the cephalothorax, and has a peculiar bend. The rostrum is often longer than the thorax. The eye-stalks, antennae, and legs sometimes attain extraordinary length, and the chelae (claws) are not always on the first pair of legs. In some species chelae are on two or three pairs of the legs. Above the antennae are expanded antennal scales, which, together with the long bases of the antennules and very prominent eye-stalks, make the head a broad and conspicuous feature. The difference between shrimps and prawns is not very well defined, the small individuals seeming to be generally called shrimps, the larger full-grown ones prawns. [pg260] Prawns are known as /crevettes/ in France and as /Garnelen/ in Germany, where they are largely used as food. In the United States the shrimp-fishery is an industry of the South. On the California coast the fisheries are very extensive and are monopolized by the Chinese.

GENUS ^Penaeus^

^P. setiferus.^ This species is about six inches in length when
full-grown. A ridge or crest extends along the center of the
carapace, and terminates in a long, pointed, toothed rostrum,
the teeth being fringed with hair on the inner side. The antennae
are a foot or more in length; there are chelae on the first three
pairs of thoracic feet; the swimming-feet and lateral margins of
the segments of the abdomen are fringed with hair; and the caudal
appendages are longer than the telson. It ranges from Virginia
southward, and is very abundant on the shores of the Southern
States, where it is gathered for the markets. The large ones are
known as prawns and the small ones as shrimps.

^P. brasiliensis.^ This species is associated with /P. setiferus/,
and, although not so abundant, forms a part of the shrimp-supply
in the fisheries. It differs from the former in having a groove
on each side of the ridge which runs through the center and whole
length of the carapace. The first three pairs of feet are chelated.
This shrimp is found as far north as Long Island, and often in
brackish water, or even where the water is quite fresh.

GENUS =Palaemonetes=

^P. vulgaris (Palaemon vulgaris).^ Average size one half of an inch
in length; body translucent, almost colorless, irregularly spotted;
rostrum as long as carapace and toothed on the upper edge. It is
found among eel-grass in brackish water, and also in pools and
ditches on muddy shores from Massachusetts Bay to Florida. Commonly
known as prawns.

GENUS ^Crangon^

^C. vulgaris^, the common sand-shrimp. It ranges from Labrador to
North Carolina on the Atlantic coast and from Alaska to southern
California on the Pacific coast. It is found in abundance on sandy
shores at low-water mark, and in shallow water below tide-mark;
also among rocks and seaweeds. When left by the tide it buries
itself in the sand. Its color varies with its location, rendering
it inconspicuous. Upon the [pg261] sandy shores it is translucent,
pale in color, and often specked, closely resembling the sand,
while on dark, muddy bottoms it is much darker. This is an edible
shrimp, eagerly devoured by fishes; it is also gathered for the
markets. The body of /C. vulgaris/ is broad at the anterior end
and tapers to a sharp point at the posterior extremity. A pair of
broad, divided appendages on the cylindrical segment, which is next
to the last on the abdomen, together with the sharp telson, form a
fan-like swimming-tail. As in all shrimps, the antennae are long and
have plate-like antennal scales at the base, which are fringed with
hairs. The mandibles are long. The movable finger of the chela is
folded across the extremity of the claw.

^C. franciscorum^, the California shrimp. This species is about
three inches in length. It is distinguished from /C. vulgaris/ by
its larger size and by the greater length of the movable finger of
the chela, which folds parallel to the side of the claw instead of
across its extremity. Its color is light or dark yellowish-gray,
mottled. This is the shrimp extensively gathered by the Chinese for
commercial purposes. The shrimp-meat is dried and cured, and then
separated by blowers very much as wheat is cleaned. It is exported
to Eastern countries in great quantities, the value of the export
being estimated at one hundred thousand dollars per annum.

CREEPING FORMS: LOBSTERS AND CRAWFISH

FAMILY ~ASTACOIDAE~

GENUS ^Homarus^

There are but three species of this genus, which is the most important one of all the /Crustacea/. They are /H. vulgaris/ of Europe, /H. capensis/ of the Cape of Good Hope, and /H. americanus/, which occurs on the eastern coast of the United States from Labrador to New Jersey. The lobster-fishery is one of great importance, and of such value that it is governed by stringent laws. The [pg262] annual catch on the Atlantic coast of North America amounts to many millions of lobsters, the money value of which is very large.

^H. americanus^, the common lobster of the Atlantic coast.
The characteristic feature of the lobster is its enormously
developed chelae, or pincer-claws, which are on the first pair of
walking-feet. Small claws occur on the next two pairs, and simple
hooks on the remaining two pairs. The appendages on the abdomen are
divided (biramous). In the female they are used, excepting the last
pair, for holding the eggs; in the male they are greatly abridged.
The appendages on the next to last segment are divided and broadly
flattened, forming with the telson a powerful swimming-paddle. The
rostrum is very prominent, and has a long, pointed end, slightly
upturned, and several spines.

The lobster belongs to the creeping forms of the order; it walks
forward by means of the ten feet, but swims backward by using its
caudal fin. It lives in deep water on rocky bottoms, hiding among
stones, etc., but frequents sandy shores as well. It lives on
dead and decaying animal matter, and it would seem strange that
its flesh is so palatable, were it not that we know that chemical
combinations which take place in the assimilation of food make one
kind as clean, when transformed, as another. All the crustaceans
have a similar dietary, being scavengers of the sea; yet fishes
find them more acceptable than other animal food, and fishes
capable of capturing larger prey subsist largely on the minute
entomostracans described elsewhere.

The lobster is so large that it can easily be dissected, and will
serve as a type of the structure of /Crustacea/. In dissecting one
can follow the descriptions given of the anatomy of /Crustacea/
on page 246, and will be interested in observing the beautiful
arrangement of the parts and their adaptation to the uses they
serve. [pg263]

The female lobster carries her eggs on the abdominal legs, to which
they are glued by a kind of cement. After the young emerge from
the egg, the zoeae still cling to the mother for a little time.
The lobster moults eight times the first year, five times the
second, and three times the third year, after which the male moults
twice and the female once a year. It retires to some secluded
spot for this operation, which is attended with many dangers. The
back splits open longitudinally and the animal slowly withdraws,
leaving the shell complete. In preparation for moulting, the lime
around the contracted joints of the chelae is absorbed, so that the
soft flesh can pass through. Any injury to a limb at the time of
moulting, or which results from fighting or from any accident, is
repaired at successive moultings, and a lost member is replaced by
a new, but not always a perfect, one.

GENUS ^Panulirus^

^P. interruptus.^ This is the California spiny lobster,
rock-lobster, or salt-water crawfish. It differs from the common
lobster /Homarus/ of the Atlantic coast in having no large claws,
the first pair of feet being simple like the rest, also in having
antennae which are enormously long and very large at the base. The
carapace is beset with spines, and the lateral margins of the
abdominal segments end in spines. This species lives among the
rocks on the southern California coast.

^P. argus^ or ^americanus^ resembles /P. interruptus/, and is found
on the coast of Florida.

GENUS ^Scyllarus^

/Scyllarus/ has a broad, almost square carapace, which is uneven and coarsely granulated; the anterior corners are sharp, the posterior ones rounded. The antennae are curiously modified into broad, flat, double plates reaching quite across the straight anterior end of the carapace. The under scales of these modified antennae are rounded and leaf-like, the upper ones are pointed. The margins of the abdominal plates on the ventral side are toothed, and on the upper side the first three sections have [pg264] knobs, the third one being the most prominent, and forming the posterior extremity when the abdomen is folded in. The walking-feet are all simple and end in points; the first pair are the longest, and the following ones gradually diminish in size. The ventral surface is rough and spiny. The abdomen is of about the same length as the carapace. These animals are found off the Florida coast and are caught in the fish-traps. They are uncommon. The very peculiar development of the antennae makes them worthy of examination when opportunity offers.

ANOMALOUS FORMS: ANOMURA

The anomalous forms which are intermediate between the suborders /Macrura/ and /Brachyura/ were, until recently, placed in a suborder, /Anomura/. The members of this group differ from one another, and some of them resemble in external features members of the other divisions of the suborders, but there is a difference in anatomical structure which separates them in the classification.

FAMILY ~DROMIDAE~

GENUS ^Hippoconcha^

^H. arcuata.^ This curious little crab, found on the Florida coast,
carries the half of a bivalve shell over its back. Its fifth pair
of thoracic legs are bent over the back, and these, together with
the fourth pair of legs and the spiny front edge of the carapace,
enable the crab to hold the shell in position. This crab was
formerly classed with the hermits, all of which were originally
called /Bernhardus/, after the monk of that name.

FAMILY ~PAGURIDAE~

THE HERMIT-CRABS

In these curious animals the posterior part of the body is not protected by a crustaceous covering, and therefore the animal seeks protection by inserting its soft and defenseless abdomen into some hollow object, usually the shell of a gasteropod mollusk, as the whelk or the periwinkle (/Buccinum/, /Littorina/). The hermit-crabs do not always use a shell for this purpose, as they are sometimes found in the tubes of plant-stems or in sponges. Like other organisms in the animal world, they seem [pg265] well fitted to make the best of their surroundings, the body becoming modified to suit the peculiar conditions under which they live. In those which inhabit shells the abdomen becomes spiral, in conformity to the convolutions of the shell. All the abdominal appendages are more or less atrophied; the sixth pair become like hooks, and these fasten to the columella of the shell, keeping the crab securely attached to it. In the female some of the abdominal appendages are hair-like and are adapted to carrying the eggs. The thorax, being protected, is protruded from the shell at will. The first pair of feet are much larger than the others, and are provided with claws (chelae). The first right foot is usually much larger than the left, and, besides the usual functions of capturing and crushing prey, the claw, or hand, serves as an operculum to close the mouth of the shell when the crab retires completely within it. The small left hand is shaped to fill out the parts of the opening not covered by the right one, thus making a close fit. The next two pairs of feet end in simple hooks, and are used for walking and dragging the crab along when he travels. These crabs move about very fast, and the houses upon their backs seem no encumbrance. [pg266]

In some genera both hands are alike; in others the left one is the larger. In the case of hermits which live in tooth-shells, the right hand is cylindrical in form, fitting the circular opening of the shell. The other extreme is found in the genus /Cancellus/, where both the chelipeds and the first pair of ambulatory feet are ingeniously shaped, so that when closed they form a round operculum, or door, which closes the way into the compact sponge which this crab has for its carcin[oe]cium, or house. It is interesting to note these differences and observe the perfection with which the feet are formed and jointed to suit the openings of different shells. Some genera show other adaptations to their twisted houses, the eye-stalks being uneven in length and the ambulatory feet unequal on the opposite sides. Besides this, some species are hairy and cover themselves with dirt for further protection. The exposed claws of some hermits have a special armature of spines, which make a fringe of points around the opening of the shell when the crab is withdrawn.